Companion planting

In their uncultivated state, plants must continually depend on their adaptability for survival. In addition to accommodating local variations in their environment, they need to compete against rival plants for their share of soil nutrients and other resources like water, sunlight, and physical space. While this competition can frequently be harsh and unforgiving, there are also situations where plants benefit from establishing mutually co-operative relationships with non related species. By closely observing nature over many years, I have learnt to appreciate and accept these complex patterns of ecological rivalry and cooperation. In turn, this provides me with a useful foundation for establishing companion planting programs within my own organic garden.

A process of discovery

To organic beginners, the concepts of companion planting may well appear inconsistent and shrouded in obscurity. I still recall examining the topic and becoming entirely frustrated by its lack of unity and scientific explanation. That was nearly fifty years ago. In the meantime I’ve mellowed considerably and am now prepared to exchange solid explanations for the flexibility of approximation and practical efficiency. I no longer feel pressured to understand the technical aspects of every situation. When a companion planting strategy works, my current approach is to relax and enjoy the success. Often there’s a scientific or technical rationale which becomes evident at a later date. I might discover this purposefully or by accident: through any combination of fortunate observation, applied research, casual reading, or conversations with other gardening enthusiasts. That’s the excitement of discovery. It can be wonderful, and deeply satisfying on occasions. Alternatively, I’m left unable to explain why a particular planting has succeeded or failed, either to myself or my friends and associates. That’s okay too. Perhaps I will figure it out sometime later.

Here are some examples of companion plantings which have succeeded in my own gardens on various occasions throughout my career. I’ll begin with plantings which can be rationalised to an extent then conclude with those which work for unknown reasons.

Combinations which promote an efficient distribution of resources

There are numerous planting combinations based upon the efficient distribution and utilisation of garden resources. It’s lovely to reap the rewards which arise from devising combinations which facilitate a mutual cooperation between distinct plant species.

The umbrella arrangement involves interspersing tall or climbing plants with several rows of shorter plants which can benefit from the physical protection and partial shade. One of my favourite examples is to plant several rows of English spinach between broadbean or sweetpea. In exposed areas, spinach requires substantial protection from drying winds and harsh sunlight. I particularly recommend this planting to warm climate gardeners who might have become frustrated by the tendency of English spinach to run to seed before harvesting.  

The most popular plantings within this category involve the positioning of shallow rooted species alongside those with deeper root systems. This enables water and nutrients to be shared while soil structure is improved by  the root foraging which occurs at separate levels. There are numerous examples which can be widely applied although their ultimate success depends upon local climate and soil conditions. Beginners might attempt a small plot combining lettuce with carrots or beetroot while experienced growers can often accommodate larger fields with productive combinations like potatoes and cabbage, or turnips with nasturtium.

Heavy feeders like sweetcorn and squashes are frequently planted alongside nitrogen fixing legumes such as beans or peas. This offers substantial protection to a soil’s nutrient profile, particularly its ongoing ability to break down and absorb organic soil additives such as dried manure, seaweed, and peastraw.

Combinations to discourage and control garden pests

A disadvantage of growing one species on a large scale (monoculture) is the devastation caused by sudden infestations of plant destroying insect. One theory suggests that monocultures produce concentrated biological signals, thereby attracting pests in significantly greater numbers, and from beyond their normal range. The introduction of carefully selected companion species weakens the attraction signals and discourages the arrival of many destructive insect species.

When cabbages, broccoli and related plants are interspersed with rows of onion, they are less prone to caterpillar and other larval infestation. This is principally due to the onion’s stronger scent and its capacity to confuse or deter cabbage moths.

Various culinary and medicinal herbs have gained reputations for their insect repellent properties. The complex aromatic oils of garlic, cloves, basil, lavender and sage will discourage aphid, fruitfly and other insects from attacking vulnerable species like citrus, rose, lettuce, and stonefruit. When planted in close proximity to seeding beds, tansy is an effective deterrent against cutworm, cabbage worms, and many types of caterpillar.

Astute organic growers frequently plant companion species to discourage pests from eating their primary crops. Redcurrants are used as a sacrificial plant to distract birds and other species which otherwise feed upon strawberries, raspberries, and blackcurrants.

Traditional planting combinations

There are traditional planting combinations which seem to work yet cannot be explained in any conventional sense. Chamomile (chamaemelum nobile) is frequently grown alongside culinary herbs where it has the effect of encouraging increased production of their essential oils and flavour characteristics. I first experienced this phenomenon on a friend’s property located near the Welsh border. He specialises in aromatic herbs like oregano, sage, and thyme. After lunch, we were invited to compare the difference between his plants raised alongside chamomile and those gathered from separate fields with a mixture of native grasses and bracken fern. I was astounded by the difference and found myself planting chamomile throughout my own herb gardens. Personal experience with this planting suggests an effective advantage which is restricted to the coarser Mediterranean and African varieties. There appears to be minimal improvement with the English, French, and Asian herbs.

Despite the conservative nature of their industry, viticulturalists are well known for the obscurity of their companion planting practices. My favourite example is the decision to grow ornamental basil between established and old growth vines. I have observed this practice on an exclusive Bordeaux vineyard renowned for the superior quality of its Grenache and burgundy varietals. In Argentina and parts of rural Spain, high quality organic grapes are occasionally interspersed between wild geranium bushes and mulberry trees. Ripening mulberries appear to attract local birds preventing them from interfering with the grapes. There is however more to these pairings than that which can be immediately appreciated by an outsider with limited conversational Spanish. I’m always fascinated by the fact that immature vines are abandoned season after season, until some combination of factors make them appealing and acceptable to the seasoned expert.

Experienced gardeners will commit themselves to few rules and even fewer certainties with companion planting. Most of us need to experiment with several approaches and will usually discover that success depends upon location, soil condition, and other factors in addition to the combinations themselves. Bearing this in mind, it is good practice to keep detailed records of each attempt so that similar conditions can be repeated whenever a successful outcome is achieved.

Insects and insect control

In recent years, there has been a considerable shift away from the chemical approach to insect control. This is often explained in terms of the increasing cost of developing new formulations to combat elevated levels of resistance within several insect populations. At the same time, the accessibility of international travel combined with progressive reductions in agricultural trade restrictions have contributed to the increased risk of introducing previously unfamiliar insect species to working farms, and gardens throughout the country. In their efforts to control troublesome insect populations, organic gardeners and primary producers depend upon a restricted range of natural products and control strategies. These can be grouped within four broad categories.

Bolstering plant resistance

The first of these include all of the efforts which seek to improve the plant’s biological resistance and resilience against insect attack. This is generally achieved by encouraging natural soil fertility and promoting a diversified ecosystem. The positive relationships between healthy soils and healthy plants provide an underlying framework for the organic approach to insect management. It is reasonable to assume that the organic emphasis on soil quality will result in improved nutrient dynamics which subsequently enable the plant to resist many forms of insect attack. The lower incidence of pest infestation on organic farms and gardens is also attributed to the biological diversity which encourages natural insect predators and resource competitors. It is important to avoid the situation where one plant species predominates over a large section of the garden. This encourages insects to establish resident populations.

Physical deterrence

The second category of insect control measures is based upon physical deterrence. In many situations, it is appropriate to remove problem insects from the garden. Destructive invaders like snails, slugs, and caterpillars can be physically removed from plants and collected in plastic buckets containing methylated spirits or saline solution. There are plenty of screens, traps, water sprays, and other devices suitable for the organic garden. Commercial insect screens and finely meshed gauze nets can be used as protective barriers against medium and larger sized insects such as fruit fly, locust, and caterpillars. When properly secured, the screens also prevent access to birds and rodents. The negative consequence of widespread insect screening can be the restriction placed on useful pollinators like bees and honeyeaters.

Many types of trap are used to capture insects. Fruit flies can be captured in plastic bottles or closed funnels containing baits which mimic the signals of sexual attraction. Slugs and snails will drown in plastic basins containing several centimetres of beer at the bottom. Traps like these can help to control insect numbers but may also be used to monitor seasonal variations in the population. This information can be used to establish crop rotations which strategically disrupt breeding and activity cycles. Sprays of water are suitable for physically washing mites, aphid, and other minute insects from foliage. Electronic or mechanical timers which initiate periodic jets will restrict most of their opportunistic movement and behaviours. Most garden centres stock a range patented devices, some of which are designed with the organic gardener in mind. Good examples are the copper strips which can be used to control slugs and snails in most suburban gardens. Individuals who loathe shopping may prefer to depend on the old fashioned remedies. One of my favourites is the use of crushed eggshell or finely ground bone fragments to protect seedlings from slugs and snails.

Natural predators

Natural insect predators provide another type of control measure. There are numerous predatory organisms which can significantly limit the destructive effects of plant feeding insects. It is possible to encourage beneficial predators into a garden but, ironically, this requires viable populations of the pest species to sustain and hold them. From an ecological perspective, the aim is to establish an acceptable equilibrium between these two populations, rather than attempting to eradicate one of them.

Typical examples of beneficial predators include birds, lizards, spiders and a host of carnivorous and parasitic insects: ladybird, lacewing, praying mantis, hoverfly, wasp, predatory mite and nematode. The presence of these species suggests that a complex, self-regulating ecosystem is established. To maintain this, a varied range of plant habitat and sheltering zones are required. Birds prefer trees and open areas; lizards seek grassy cover and hollow logs. The predatory insect species usually depend on nectar or fruit bearing plants to attract their prey.

Biological control

Biological control is also dependent upon identifying species which prey or compete against an established insect pest. Unlike natural insect predators, the majority of organisms used as biological control agents are manipulated by some human intervention. This may involve breeding programs in which an introduced species is released in populations of sufficient size to impact upon the nuisance insect. Biological controls in agriculture are frequently established within the field of microbiology. Various microorganisms such as bacteria, fungi, viruses, and protozoa can be manipulated to improve aspects of the organic ecosystem. These interventions will be ecologically sensitive and expensive, so are usually restricted to specialist growers with sufficient resources and government approval. At the lower end of the scale, many organic gardeners are familiar with the microbial based insecticide known as Bt. This product is developed from selected strains of Bacillus thuringienis bacterium, which releases a natural toxin killing many species of caterpillar and other destructive larvae within several days.

In some situations, an insect population may eventually adapt and become resistant against the individual control strategies described here. Experienced organic gardeners will routinely vary their approach, particularly during prolonged breeding cycles and periods of seasonal acclimatisation when normal resistance is diminished. Dependent upon local growing conditions, there may be opportunities to combine several of the outlined strategies for insect control.

Diseases and disease control

It is estimated that a majority of organic gardeners will be challenged by several outbreaks of plant disease during each growing season. This statement never fails to alarm a small percentage of faces in my audience. I quickly identify them as worry prone gardeners. Occasionally, they will approach me following a speaking engagement. Some of them possess an encyclopaedic knowledge of plant disease. They worry and fret over every perceived blemish. Patchy lawns, curled leaves, mottled bark, misshapen flower buds, and so on. After brief discussion, I appreciate their anxieties but cannot genuinely help them. I have also encountered the opposite reaction in gardeners. There are a minority of individuals who refuse to acknowledge serious problems when they occur. Surrounded by obvious and widespread symptoms, they somehow prefer to avoid any of the assertive actions required. While both behaviours can probably be attributed to some form of fear, I would personally prefer my closest neighbours to be the worry prone - as opposed to oblivious - variety of gardener.

While I have certainly chosen to describe two polar extremes of gardening behaviour, we are all capable of unnecessary panic, and neglect on occasions. At the present time, there are no magic bullets, nothing in the manner of a universal remedy which will safeguard our plants and gardens from the threat of disease organisms.

All we depend upon is resourceful intelligence and experience. Disease prevention and control can be simplified to compose four basic objectives.

• Disease risk analysis
• Identification of significant disease symptoms
• Strategies for prevention within an organic framework; and
• Control and treatment measures that can be safely applied within the integrated organic environment.

Let’s consider these in a little more detail.

The analysis of disease risk

Plant and soil borne diseases are classified by the biological status of their active pathogen. The commonest pathogens are the microscopic fungi, bacteria, viruses and nematodes. Most of these pathogens are opportunistic, surviving in small numbers until prevailing conditions enable them to rapidly multiply. Following this stage, it is usually possible to identify visible symptoms although these will vary according to the types of plant affected, the climate, soil condition, and the virulence and progression of the active pathogen. Experienced gardeners will also appreciate that the risk of encountering any particular disease will depend upon a similar combination of factors. In most situations the risk can be approximately determined by a careful assessment of the local and seasonal growing conditions, availability of quarantine protections, and the susceptibility of individual plant species.

For every organic gardening forum I attend, I always expect to learn at least one thing which totally surprises me. Inevitably, the majority of these surprises relate to the peculiarities of a particular geoclimatic situation. I’m constantly telling people there’s no substitute for accurate local knowledge. The most effective gardening strategies are based on specific as opposed to generalist sources of information. This is never more fully demonstrated than the practical aspects of disease risk assessment. Here’s my advice. Purchase a fifty cent notebook and visit your closest public library. Search for publications released by the official departments of agriculture and primary industries. Focus on the most recent reports which describe horticultural diseases and quarantine regulations. While influenced by the local impact of common plant diseases, they also provide some indication of recently introduced strains and those most likely to threaten commercial growers and native species. The next step is to visit local plant nurseries, garden centres, and plant breeders. Ask general questions about local growing conditions. Look carefully at the plants and ask relevant questions. The technical staff will often be trained to provide practical information about the identification of healthy as opposed to symptomatic plants.

If you haven’t already done so, it is time to join the local branch of the organic society. Many participants will be experienced gardeners prepared to share their knowledge on various plant diseases and the level of risk pertaining to these.

Identification of disease

Early detection of plant disease makes it easier to control the spread and thereby limit any negative effects within the garden. The ability to recognise early stages of disease depends upon some understanding of the normal appearance and life cycles of susceptible plants. Excellent information can be sourced from illustrated gardening encyclopaedias and specialist botanical publications. Establishing a routine of physically checking each plants condition is the best way to consolidate and apply the information sourced from books. Early to mid morning and late afternoons provide a softer light, ideal for inspecting foliage, particularly when the magnification of a hand lens is required. Any signs of abnormality should become apparent when compared with that of healthy growth and reproduction.

Prevention strategies 

Plant stress is always a significant risk factor for susceptibility to disease, so avoid overcrowding and preferably choose varieties which are well suited to local conditions. Where individual species are particularly vulnerable to certain diseases, it may be possible to obtain strains developed for their improved resistance. Alternatively, when these are unavailable, it may be wiser to choose plants from a different family. Healthy plants develop their own immunity which provides the best natural defence against most forms of disease. Optimum immunity requires superior genetics, steady growth, and a track history of survival.

It is important to choose and maintain healthy garden sites for the majority of plant species. Damp or stagnant areas can eventually provide refuge for troublesome plant diseases. It is surprising how many disease organisms are destroyed or greatly weakened by sufficient exposure to sunlight and clean circulating air. The lack of sunlight and circulating air appears to contribute to the general susceptibility of many indoor plants.

A soil which is periodically enriched with compost and other organic materials can help plants maintain a steady rate of growth. The excessive use of nitrogen-based fertilisers tends to encourage a sudden proliferation of foliage which may eventually reduce plant vigour and increase susceptibility to disease. Synthetic chemical fertilisers will also deplete the concentration of microorganisms which are essential for breaking complex soil nutrients to a form which can be used by plants. One of the newly emerging garden products are concentrated supplies of these healthy bacteria which can be applied directly to soils to encourage new generations of living organisms. This reflects the organic philosophy of building balanced ecosystems where complex life is intricately connected and ultimately dependent upon the microscopic soil organisms.

When introducing new plants, quarantine them for at least a couple of weeks before planting. To further reduce the risk of introducing disease, all seedlings, mature plants and soil products should be obtained from reputable organic suppliers.

Control and treatment

It is rarely possible to identify a single cause for any disease outbreak. Sudden changes in temperature, rainfall, or soil chemistry can cause microscopic pathogens to be activated from a dormant state. This may precipitate a localised outbreak of disease, but the consequences will vary according to the control and treatment measures applied. The best of these will reduce or eliminate the need to pursue chemical and other potentially harmful remedies.

One of the most effective control measures is to rapidly isolate and contain the originating source of any minor disease outbreak. The isolation of transmissible plant disease requires strict attention to garden hygiene. Many diseases have the potential to spread quickly when infected materials are carelessly handled or disposed. I own several gardening books which recommend deep burial although I generally prefer incinerating diseased and suspect plant materials. Pathogenic fungi spores and bacteria can be carried into healthy sections of garden through the action of wind, browsing animals, and on the footwear or clothing of humans. Wiping garden cutters and other frequently used tools with a sterilising alcohol helps to lower the possibility of transferring disease.

For most gardeners, soil borne diseases are particularly difficult to detect and isolate. Over many years, I had noted that mulched garden beds tended to have significantly fewer incidences of plant disease. It wasn’t until overhearing a comment from an organic strawberry grower that I discovered the likely reason for this. Mulching restricts disease transmission by preventing infectious spores splashing onto plants. It also provides a natural weed control which reduces the need for constant digging and soil disruption.

Until recently, organic certification authorities have allowed commercial producers to use simple fungicidal compounds based on copper, tin, and sulphur. These are effective when administered as powdered or gelatinous agents, controlling a spectrum of fungal disease across diverse plant species including tomatoes, cocoa, potatoes, and grapes. At present, there is a new wave of restrictions coinciding with greater regulation of the various organic industries and the contribution of international trade bodies. This has caused a considerable amount of resentment, particularly among growers attached to the organic wine and beverage industries.

According to my own evaluation of mainstream organic sentiment, there is an approximate division as to whether these substances should be used in horticultural production and general gardening pursuits. From the historical perspective, these preparations appear to have been used with remarkably few adverse effects. One of the arguments for restricting copper compounds is their potential toxicity and the risks associated with ingestion of treated materials. The other concern raised by the organic purists is their possible effects upon soil chemistry and the balance of microbial life forms. Longitudinal testing of vineyard soils in France, Canada, and the United States have, for example, revealed significantly elevated copper concentrations combined with deficiencies of zinc, selenium, and other trace minerals. In view of these findings, I have avoided the use of copper compounds for several years. I occasionally use sulphur dust on my tomatoes but am increasingly shifting toward the use of home made herbal extracts for fungicidal control.

Natural remedies against fungal diseases can be made at home from seaweed and various herbal extracts. I have discovered that infusions of nettle, spring onion, or chamomile are excellent for controlling troublesome mildew on squashes, cucumbers and other climbing vines. To ensure adequate potency, the nettles, spring onions, or chamomile flowers must be carefully harvested from high quality stock. I tend to harvest chamomile early in the spring but keep a reasonable store of the dried flowers for later in the season when fungal problems are on the rise. The flowers or leaves are soaked in boiling water for several minutes. After cooling, the liquid extracts should be diluted to a weak tea consistency. Strain these with a fine muslin filter prior to application. For best results, the strained liquids should be transferred sealed canisters and used within approximately two weeks. In addition to their gentle fungicidal properties, nettle and seaweed foliar sprays provide a range of beneficial plant nutrients.

For those of us living within reasonable distance to the coast, seaweed or kelp can be gathered in abundance after a storm. I know gardeners who fill their trailers several times each year. Unlike many of the chemical fungicides, kelp solutions are entirely safe and simple to prepare. I remove excess salt with a careful rinsing before soaking the long strands inside a plastic basin containing fresh water. After approximately two weeks the concentrated kelp solution should be diluted to the consistency of weak tea. Strain through muslin filters to remove any solid particles then transfer the remaining liquids to a sealed canister. There’s no reason why a kelp solution cannot be stored for several months, although I tend to prefer mixing new batches once the storage period extends beyond a couple of weeks.

Natural sprays

There are several botanical and naturally derived substances which can be sprayed in the organic garden to control pests and disease. Widely used before the arrival of chemical products, several of the natural alternatives have become less fashionable and may be difficult to obtain.

I first appreciated the benefits of natural garden sprays several years ago when I helped a close friend whose vegetable gardens became infested with a particularly virulent species of cutworm. Around the peak of spring, she attempted to control them with a well known chemical treatment. Despite repeated applications, the number of cutworm began to increase rather than diminish. By the approach of autumn, her summer vegetables were all but devastated and my friend became reluctant to attempt a winter crop.

When she requested assistance, my initial plan was to work steadily on the soil. By increasing the quantity of organic materials, I hoped to improve the soil’s nutrient distribution and simultaneously encourage the larval predators which might eventually control the cutworm problem. One of my local contacts suggested a heavy dose of natural insecticide. He gave me the address of an elderly gentleman with his own pyrethrum recipe. Now I considered myself sufficiently knowledgeable to dismiss pyrethrum for treating cutworm. A significant dose might control caterpillars and leafhoppers, but would probably be ineffective against serious cutworm infestations, I predicted. Natural pyrethrum breaks down to nothing within a few days. “Cutworm”, I asked doubtfully, “you’re convinced this will control cutworm?” The old gentleman touched his nose. “Yeah”, he said. “It’ll get ‘em”.

And it did! Within several days the cutworm were history. After that result I returned with a few questions. The pyrethrum supplier referred me to a publication on natural garden sprays. It was currently out of print, so with his permission I reproduced a couple of sections for my own reference. There was an insightful chapter on safety precautions required for the preparation and application of natural garden remedies. I was concerned by the toxicity of several plant derived insecticides, particularly the nicotinic and anabasinic compounds.

Nicotine-based insecticides are extremely poisonous to humans, domestic livestock, pets and native animals. Thankfully, I’ve managed to avoid these particular compounds, although many of my friends have recommended them to me. I prefer relatively safe natural compounds such as rotenoids and pyrethroids. These can still occasionally be purchased from local garden centres and organic suppliers.

It appears that toxicity of natural rotenoid compounds was initially exploited by indigenous South American tribes who used various plant extracts to paralyse fish. Organic gardeners may be familiar with the insecticide products based on these compounds. Derris powder is the most popular extract from plants of the genus rotenone. The product is still prepared by mixing the finely ground plant roots with a clay base. When sprayed appropriately, derris is effective as a general insecticide. Unlike the majority of fast acting insecticides, rotenone does not function as a nerve toxin. It is believed to inhibit oxygen transport and basic energy mechanisms within cells. It is extremely toxic to fish and amphibians, so care is required when spraying near rivers, creeks or ponds.

Organic pyrethrum

Organic pyrethrum is the botanical extract from pyrethrum flowers (chrysanthemum cinerariaefolium). This is distinct from synthetic pyrethroids which are chemical approximations of the naturally occurring compounds.

When formulated as liquid or aerosol, natural pyrethrum compounds prove rapidly effective against a wide range of insects. The knock down effect is particularly evident within enclosed environments such as greenhouses, propagation sheds, and indoor gardens. In higher doses, it can be effective in orchards, and other outdoor settings. Like derris, organic pyrethrum will break down completely after several days exposure to sunlight.

On the positive side, they are considered as one of the safest insecticide compounds with a low toxicity to humans and other warm blooded mammals, although some skin irritation and allergic reactions have been associated with repeated handling and use. Unwashed traces of pyrethrum compounds are usually destroyed by exposure to heat, sunlight, and other atmospheric influences. Negatively, pyrethrum is toxic to fish, amphibians and indiscriminate applications can obviously harm beneficial insect organisms such as pollinators and natural predators.

Since my encounter with the cutworm, I’ve received numerous enquiries about the availability of natural pyrethrum compounds. There is a general consensus that it’s becoming more difficult to obtain. Commercial crops of pyrethrum flowers are grown in Africa, Japan, and Hawaii, although the volume of production has declined significantly over recent decades. Within most organic gardening communities, there are individuals and groups who continue to raise pyrethrum chrysanthemums for the purposes of insect management. My advice is to contact the nearest organic society. They can usually provide the best indication of local availability.

Microscopic pests

The majority of nuisance insects which attack our plants from one season to the next are tiny, almost microscopic in size. Once they have identified their plant hosts, many of these pests will generate large colonies within a surprisingly short period of time. In addition to encouraging their natural predators, minute insects can be controlled with natural substances which remain effective for at least several days.

Various light oils are used to control scale, mites, thrip, flies, and many of the softer larvae which attack foliage. They work by interfering with the insects normal mechanisms of respiration, feeding, and temperature regulation. To eliminate the risk of leaf damage, these products can be sprayed when the shrubs and trees enter their dormant winter phase. Insecticidal soaps are also made from botanical oils combined with the salts from natural stearols and other fatty acids. When applied in solution to foliage, they are an effective treatment against soft-bodied thrip, mites, aphids, and flies. During times of infestation, they need to be applied several times each week although some sensitive plants can develop leaf burn with repeated applications. A weaker solution should eliminate leaf burn or assist by reducing the severity of the problem.

No magic bullet

Since committing myself to an organic approach, I’ve attempted to understand each living garden as a complex and integrated environment. Given this, I try to avoid the imbalances which can accumulate whenever insect populations are rapidly affected by toxic compounds. In short, I remain suspicious of the magic bullet approach, even when this involves natural compounds such as pyrethrum. Once again, I admit struggling to appreciate how an old-fashioned pyrethrum solution was so devastatingly effective against my friend’s cutworm problem while the contemporary chemical treatments had simply failed. The reasons were quite obvious, yet I needed time to reflect upon them.

With few exceptions, synthetic chemical products establish a toxicity which lingers in the soil for an extended period. Under these circumstances insect populations are provided opportunities to adapt, and develop their own resistance against the chemical agent. Most of the local cutworm population were probably killed through initial contact with the synthetic chemicals, although a small percentage may have survived then experienced a significantly reduced exposure over an extended period of time. It is these low level exposures which promote adaptation and, ultimately, resistance. By contrast, the residual toxicity detectable at several days following the pyrethrum treatment would have been negligible. Any surviving insects would be denied the benefits of adaptation. For this reason alone, it is often recommended that pyrethrum be used as a high potency single strike application rather than as a modest dosage regularly applied.

To date, my friend has raised many vegetable crops without the impediment of the serious cutworm infestation. We remain thankful for the effectiveness of the pyrethrum treatment although both of us believe that the decisive remedy was founded upon our integrated and longer term strategies of soil improvement and the encouragement of natural insect predators.

Crop rotation

I try to avoid gardening publications which provide simplistic crop rotation schedules. Most of these apply somewhat narrowly to vegetable plots, and fail to address the entire garden as a complex biological entity. They also tend to be inflexible with regard to the seasonal preparation and selection of individual plant species. Most of my understanding of crop rotation is derived from a combination of agricultural textbooks and practical garden experience. Over the years, I’ve attempted to develop my own system of garden rotations. I have enjoyed reasonable success on several private estates in the northern hemisphere and am presently adapting my approach to suit smaller gardens in a considerably warmer climate. I will describe the basic principles and benefits of crop rotation. For specific enquiries on this topic, please contact me by using the comments section that appears below this article.

What is crop rotation?

Crop rotation is an agricultural system where related species are grown together in one area which is harvested then replanted with a different family of plants the following season. In its various forms, crop rotation has been practiced for thousands of years. Roman influences upon Britain and Continental Europe contributed to the basic three field rotation which became widespread during medieval times. Initially designed to provide spring and winter cereals, the rotation schedule was later modified to include pasture, and high value crops like sugar beet, potatoes, and hops. In many respects, crop rotation improved agricultural production to a level which enabled states to expand and develop their political and economic stability. The historical impact of crop rotation was determined by a series of biological factors which remain relevant to anyone interested in growing healthy plants without the widespread use of toxic chemical treatments.

It is widely understood that families of plants have varying nutrient requirements and these will place certain demands upon the soil. One of the aims of crop rotation is to avoid a situation whereby similar soil nutrients are required by one family of plants over consecutive growing seasons. This can be achieved by rotating distinct plant families in a logical sequence. For example, vegetable crops in the brassica family (cabbage, broccoli, kale) are heavy feeders which require plenty of nitrogen for rapid leaf growth. At the conclusion of their growing season it is beneficial to replant the area with legumes such as peas, beans, and lentils. Legumes have fewer nutrient demands and actually initiate an enzymatic process which fixes nitrogen, improving its availability for future crops. In addition to preserving the nutrient profile of extensively cultivated soils, crop rotation can offer protection against various toxins which are released by plants themselves. When allowed to concentrate in a soil, these toxins may restrict the normal activity of soil microbes. This will eventually create an unsatisfactory environment for the recycling and utilisation of organic materials.

Controlling insects and disease organisms

Most of my efforts in developing plant rotation schemes have been focused on the control of nuisance insects and disease organisms. In order to survive and thrive, a majority of plant destroying pests and disease pathogens must concentrate and establish themselves within a particular territory. Insects are usually attracted to suitable host plants by visual characteristics, smell, taste, and other chemical signals. When their favoured crops are rotated to different locations, the destructive organisms have their breeding cycles disrupted. With few exceptions, juvenile insects and larvae are particularly vulnerable to relocation of their normal food supplies. In attempting to overcome the barrier of distance, many will be taken by garden predators such as ants, spiders, lizards, and birds. To control plant pests, rotation schedules must be flexible enough to accommodate the seasonal shifts which can result in the early or late arrival of new generations.

There are plenty of gardening books suggesting that plants should be grouped according to their susceptibility to certain pest and disease conditions. In my experience, there is little to be gained from this approach. On many occasions I have discovered that susceptibility cannot be entirely inherent in the plants themselves. I have seen strawberry plants thrive in one garden location while alternately sited runners from identical stock were repeatedly destroyed by aphid. It appears that functional susceptibility is largely dependent upon the complex interactions between local garden conditions, pest populations, and natural plant resistance. The correct appraisal of local garden conditions should include aspects of seasonal climate, plant distribution, soil structure, composition, including the variety and concentration of microbial soil organisms. The majority of pest populations are more readily controlled by interventions which directly influence these factors.

Rather than focusing upon the particular susceptibilities of individual plant species, pest problems may be solved by a broader process of observation and analysis. The aphid infestation was eventually corrected by adapting the rotation schedule to avoid open sites. By rotating strawberries across locations with varied assortments of cover vegetation, we provided suitable accommodation for the aphid’s natural insect predators. Within several seasons, the aphid population was diminished to a harmless capacity.

The organic application of crop rotations can also be based on obtaining maximum efficiency and productivity with minimal risk to long term soil fertility and the environment. A carefully planned rotation schedule can also reduce some of the physical work associated with herb and vegetable gardening. Carrot and root crop seedlings require loose soil. Instead of digging the ground, the seedlings can be directly planted to a section which has already raised shallow root crops like lettuce followed by deep rooting plants like tomatoes.

Good growing practices to control pests and diseases

My old colleagues and friends still scratch their heads and laugh at me. Many decades ago I carried a very important key. It opened the door of a triple bay storage shed, stacked with numerous horticultural chemicals. With tireless regularity, I applied these to control the pest and disease organisms which attacked the various plants under my care. One morning, I woke up and said no more. I had been studying the organic approach to insect and disease control quietly for several years, but remained uncertain how to make the necessary changes on the estate. In the end, we agreed to embrace organics with a sink or swim approach. I readily admit this was more than challenging for an initial few seasons.

There were several steps to establish a working organic environment. We commenced a thorough evaluation of local conditions, determining the prevalence of various plant diseases, insect pest, and predator species. Success then depended upon choosing the set of control procedures which were most suitable for replacing our dependence on the chemicals. Many of the control procedures were labour intensive and required considerable amounts of research and fine tuning to accommodate the specific requirements of our garden. Fortunately, I was mentored by a well respected pioneer of the organic approach. His detailed and objective journal records revealed significant progress by the commencement of the third season. I make some point of this because the incremental achievements and overall success had been almost buried amidst my elevated expectations and desire to achieve positive results in the shortest amount of time.

Constant learning

Approximately four decades later, I’m still learning the importance of self restraint and patience. Thankfully, I’m no longer tempted to abandon organics and spray my plants with chemicals to facilitate a hasty solution for insect and disease problems. As my original mentor once explained, the organic approach is about creating balance between healthy soils, and the biological ecosystems which include garden plants, and the various organisms which seek to destroy them. I suppose it’s a theory which accepts opposing influences rather than attempting to eliminate one side of the equation. Adopt this mindset and you’ve basically found the road heading towards practical organic solutions. From then on, proceed to accumulate relevant knowledge, remain calm and be prepared to stay the course.

Risks to plant health

Despite common misperception, the influence of pest and disease organisms does not represent the major risk to plant health. When statistically measured, the most negative impact on plants is bad weather, followed by poor husbandry and management. Basic errors associated with watering, feeding, and overcrowding are directly responsible for more losses than any combination of disease or pest. Having clarified this, it is important to acknowledge that plant resilience and immunity may be progressively weakened by any sequence of negative events. For example, an immature plant receiving poor management combined with unfavourable seasonal conditions will be more vulnerable to pest and disease problems than an established specimen which is well managed and unaffected by inclement seasonal factors. These observations support the organic philosophy of providing plants with the best available conditions and resources to enable them to naturally resist disease and predation.

Approaches to pest and disease control

There are several popular strategies and remedies available to assist the organic gardener to control insect pests and disease. The most effective approach is to build an integrated system which mimics the checks and balances occurring in nature. An integrated system should combine the fundamental aspects of plant husbandry with a selection of preventive and remedial strategies. Effective plant husbandry involves the strict maintenance of garden hygiene, the provision of healthy soils and growing conditions, in addition to the selection of plant varieties exhibiting some natural resistance to locally prevalent disease and nuisance insect organisms.

Disease and insect problems are less likely to affect gardens where basic hygiene and quarantine rules are practiced. Many garden resources such as soil, seeds, or plant cuttings are capable of transmitting disease or pest infestation when introduced from affected areas. Aside from restricting their entry, the best protective measure is to quarantine any risk associated materials introduced to the garden. Where practical, a quarantine area can be designated, preferably one offering a degree of physical isolation from the rest of the garden. By applying a strict observation period of several weeks, the likelihood of detecting any outbreak is increased along with the opportunity for containing and destroying the culprit. The risk can be further minimised or eliminated by obtaining plants and other stock with certified disease free status.

Wind, birds, insects, and other animals are also capable of spreading plant disease. Symptoms may occur on any part of an affected plant include mottling, discolouration, wilting, and holes or notches in the foliage. Regular observation and inspection is essential throughout the garden, to ensure that minor infestations can be controlled or eliminated before they become established. With experience and research, it is possible to gain basic understanding of the life cycle and behaviour of the organisms causing damage to plants. This effort is usually rewarded with practical results such as earlier detection and more effective control strategies.

Suitable conditions

In order to support the natural health and resilience of plants, it is important to consider the most fundamental aspects of their growth and development. Selecting an appropriate site, one which provides the required sunlight, temperature and soil conditions is critical. The ability to accomplish this for some of the less common plant species can depend on specialist knowledge and practical skills which are sometimes obtained only through initial error and persistence. Healthy and vigorous plants depend upon their growing medium to provide a complex range of nutrients. Compared with their wild cousins, many cultivated plants are less equipped to compete with other species for their water and nutrient requirements. In practice, they may require their own dedicated site where they benefit from enriched soils with adequate drainage characteristics. The nutrient cycle of cultivated gardens can be improved by the practice of crop rotation and the provision of complex organic soil conditioners.

Plant selection will ultimately determine the success of strategies used to control nuisance insect and disease organisms. By selecting strains containing a natural resistance, organic plant breeders have carefully developed their own varieties which are resistant against the pest and disease organisms which most commonly affect the species. Examples include carrots with superior resistance to whitefly, potatoes less affected by blight, and a lesser susceptibility to fungal infection for tomatoes and vine fruit. In many instances, it makes sense to choose these hardy varieties, particularly where climate or soil conditions are likely to contribute to plant stress.

The widespread use of synthetic pesticides is a relatively recent phenomenon, with its technological foundation emerging from the development of chemical weaponry during the Second World War. By comparison, remedial and preventive strategies available to organic practitioners are based on modification of various agricultural applications which were once widely used to control insect and disease problems among edible crops and other plants. Companion planting, beneficial predators, physical barriers, and organic sprays are all considered to be common or essential practice within integrated systems of pest and disease management. These organic methods of control will be slower and their results less dramatic, compared with most of the currently available chemical treatments. The main advantages of the organic methods include environmental safety, protection of bio-diversity, and their contribution to healthy soils and a sustainable approach to gardening.

Attracting birds to the garden

A complex and natural garden must include a variety of birds, some resident, others frequenting as seasonal visitors. Many species can be attracted by providing their basic requirements of food, water, and shelter. The two types that will be most important are the fragile nectar eaters, and those that feed exclusively on insects. The nectar eaters such as hummingbirds contribute by pollinating flowers and fruit. Small, agile species of wren, thornbill, and several varieties of finch will assist with the control of insects by capturing and devouring large quantities, particularly when raising their young. Larger vegetarian and omnivorous birds such as parrots, cockatoos, and members of the crow family can be destructive as can species like starling which congregate in very large flocks.

A safe environment

To be comfortable and safe, most species of birds require different levels of vegetation, beginning with tall grasses for ground cover and feed, compact elevated shrubbery or hedges for protection against the elements, and tall trees for safety against predators, nesting, and observation of their territories. The neighbourhood presence of domestic cats is a predatory threat to birdlife, particularly native species which often lack the speed, agility, and experience to avoid capture. Warning bells attached to a cat’s collar can help save birds as can the careful positioning of popular facilities such as feed stations, nesting boxes and water baths. The nest boxes definitely need to be elevated then hidden from view. Water fountains and feed tables should be placed in safe, open spaces with no concealment or cover for stalking hunters. Many local councils have developed campaigns to eradicate ferals while controlling numbers of domesticated pets through registration and spaying. Despite appearing harsh, such initiatives should be encouraged by anyone interested in protecting or maintaining a healthy representation of native birdlife.

Dietary patterns

When planning a garden to attract native birdlife, it is worthwhile observing and researching their seasonal dietary requirements. Smaller species in particular, tend to have fast metabolisms requiring them to feed frequently on a wide variety of foods. A good selection of flower and nectar producing plants will attract a regular supply of insects along with the birds that feed on these. Shrubs that yield a berry crop or those with pods containing seeds are well received by ground foraging species. Leaving the seed heads on flowers until the birds have visited will ensure that these rich stores of energy are properly utilised. Water features can also be useful for attracting birds, particularly in dry climates.

Feeding stations can be filled to attract migrating and transient species during the winter months. A range of hard and soft foods including sunflower seeds, millet, fresh greens, mashed potatoes, and porridge can be served each morning then removed by evening to avoid encouraging mice or rats. Local species may prefer feeding within their native habitats.

Loss of native bird populations

During the previous century, most urban and rural locations have suffered serious depletions of their native bird populations. The causes of this are complex but usually include degradation of habitats, chemical toxicity within food supplies, lowered immunity, and competition from introduced species. When a population retreats or disappears from an area, considerable effort and encouragement is usually required to restore them. Even when appropriate conditions are re-established, years may elapse before they return in acceptable numbers. Frustratingly, birds are far easier to lose, apparently overnight. If a garden fails to provide safe conditions, or the appropriate types and quantities of food, most of the birds will rapidly disappear in search of new habitat.