A hoverfly on a leaf

Organic gardening combines several complementary strategies to achieve healthy crops. These strategies consist of an array of simple gardening practices that will greatly reduce the impact of pests and diseases.

And in the event that a problem does occur, there are simple, effective remedies that will not poison your soil, your crops or the people who eat them.

Always identify any suspected pests and diseases before acting to control them. About 95 per cent of insect species in the garden are beneficial, keeping pests under control, or they are harmless.

Only use sprays when pests and diseases are causing significant damage to crops. Indiscriminate spraying can kill beneficial insects and increase your problems.

Good garden practices

Research has long demonstrated that pests prefer to attack sickly plants. So feeding your soil to produce plants that are bursting with vitality not only results in bumper crops but also helps to deter insects.

Avoid fast-acting nitrogen-rich chemical fertilisers. Not only do these fertilisers damage the micro-organism and earthworm population in the soil, but the quick flush of sappy, tender growth that they generate in plants is a magnet for insects and diseases.

Compost and well-rotted manures provide a steady supply of a very wide range of nutrients and are also rich in valuable micro-organisms. Regularly adding compost to the soil is probably the single most important thing you can do for your garden’s health. It should be possible to literally dig the soil with your hands.

If you feel a crop needs a boost, use seaweed or fish liquid fertiliser. Both give a balanced supply of nutrients and a burst of healthy growth.

1. Water

Drought-stressed crops are more vulnerable to attack. But your plants’ water requirements can be halved if you dig generous amounts of compost into the soil and use organic mulches. This is especially important given the effects of climate change.

Help control fungal diseases by watering in the morning; this ensures that crops are dry overnight. Stay off garden beds when the soil and plants are wet to avoid soil compaction and reduce the spread of fungal diseases.

Mulching also insulates the soil and reduces large daily fluctuations in soil temperatures. These fluctuations occur particularly in summer, stressing plants and increasing their susceptibility to attack. Mulching also prevents soil splash, which encourages infection by soil-borne fungi such as Botrytis.

2. Air and sunlight

Plants require good air movement and adequate access to sunshine to ensure pests and diseases do not thrive in high humidity. Pruning, training and good site selection all contribute to improved air circulation.
A compost heap with flowers on top

3. Sanitation

Clean up garden waste and dispose of it promptly. Never place infected material on the compost heap, where it can start a new cycle of infection.

4. Solarisation

Covering infected soil for several weeks with black plastic secured around the edges – can be used to heat-sterilise the soil.

5. Crop rotation

To avoid building up a reservoir of pests and diseases, rotate crops around the garden. Keep track by creating an annual planting rotation plan on paper. Let at least three years pass before repeating a planting of related crops, such as brassicas, in the same place.

6. Attract natural predators

Many problems can be prevented or controlled by attracting beneficial insects into the garden, such as lacewings, hoverflies and ladybirds. Biological controls – specially bred populations of predatory insects such as ladybird larvae and predatory mites – are available for purchase and release from a number of companies.

A ladybird on a leaf

Attract beneficial insects like ladybirds into the garden

7. Right time, right crops

Crops that are planted too early or too late, that are suited to a different climate, or that require a pH very different from your soil’s pH will rarely flourish. They will therefore be more susceptible to pests and diseases. For example, brassicas that are planted in the summer heat are far more prone to attack by diamondback moths.

8. Avoid monocultures

Planting a large patch of a single crop is like inviting insects and diseases to a continuous feast. Interplant small blocks of individual crops with other crops, herbs and flowers that attract beneficial insects.

9. Choose resistant varieties

Choose non-hybrid varieties bred for disease resistance if possible. Hybrids may have resistance, but many have been developed primarily for commercial once-only harvesting. Also, their seeds will not breed true. Heirloom varieties, often treasured for centuries for their reliability, vigour, resistance and flavour, have become very popular with gardeners worldwide.

10. Companion planting

Companion planting relies on the action of plant exudates – substances that plants exude, such as essential oils, that have different effects. These can include disrupting the ability of insect pests to target specific plants. For example, planting anise in the vegetable garden repels aphids, while catnip repels weevils and squash bugs.

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