Organic pest control: a practical guide.

The approach, in order

Organic pest control is not one product that replaces a spray. It is an order of work. The RHS puts it plainly: good cultivation, the right varieties, garden hygiene and encouraging natural enemies should be the first line of control, and a chemical, if you ever use one, is the last. Garden Organic starts in the same place, with a healthy soil that grows strong, resistant plants.

So we work down this list. Each step does more of the job than the one below it, and most gardens never need to get past the middle.

The point of the order is that the early steps are free, permanent and harm nothing, while the late steps cost money, need repeating and risk the very wildlife doing the work for you. Spend your effort at the top.

Prevent: healthy soil, right plant, right place

Most pest problems are a symptom. A stressed plant in the wrong spot is a soft target; a strong plant in good soil usually copes. Garden Organic is direct about it: a healthy soil produces strong, resistant plant growth, so feeding the soil is the first thing you do for pest control, not the last.

• Build the soil. Add home-made compost and mulch so plants root deeply and grow steadily rather than in soft, sappy flushes.
• Right plant, right place. Match plants to your sun and shade and your soil type. A plant that suits its spot is not fighting for its life and shrugs off pressure.
• Choose resistant varieties. Where a crop has a known enemy, a variety bred to resist it saves you most of the work.
• Ease off the nitrogen. Too much nitrogen-rich feed pushes soft, leafy growth that, as Garden Organic notes, is exactly what aphids want. Feed for health, not for size.
• Rotate and tidy. Move crops around with a crop rotation so pests do not build up in one spot, and clear away the debris that shelters them.

Exclude: barriers that keep pests off

If a pest cannot reach a plant, it cannot damage it. A physical barrier is the most reliable control there is, because it does not depend on timing, weather or wildlife turning up. The trick is to get it on before the pest arrives, not after.

• Insect mesh and fleece. A fine mesh or fleece laid over a crop keeps flying and crawling pests out. Garden Organic rates fleece as excellent protection; an ultra-fine mesh stops even tiny flies.
• Netting. Netting keeps birds and larger pests off fruit and brassicas. Keep it taut and check nothing can get trapped inside.
• Collars and grease bands. A cardboard collar round a stem base blocks some soil pests, and a grease band round a fruit tree trunk stops crawling insects climbing up.

Barriers are the mainstay of controlling specific pests. For the two that cause gardeners the most grief, see our full guides to slugs and snails and vine weevil.

Encourage predators: let the garden do the work

Every pest has something that eats it, and a garden full of those natural enemies polices itself. This is the step that pays back for years: build a place predators want to live and breed, and they keep pest numbers down without you lifting a finger. The RHS lists the aphid eaters alone as ladybirds, ground beetles, hoverflies, parasitoid wasps and earwigs, before you even count birds and lacewings.

You attract them the same way you attract any wildlife:

• Grow the flowers they feed on. Hoverflies, lacewings and ladybirds are drawn in by nectar and pollen, and Garden Organic singles out fennel, coriander and cow parsley for parasitic wasps. Our guide to planting for pollinators covers the same plants that bring in these beneficial insects.
• Add a pond. Even a small one brings in frogs and toads, which work through slugs and other pests after dark.
• Leave shelter. Log piles, leaf litter and a gap under the fence give ground beetles and hedgehogs somewhere to live and hunt.
• Feed the birds. Blue tits clear overwintering aphid eggs and song thrushes take snails; a garden that holds birds all year holds their appetite too.

Biological controls: a targeted boost

When a pest gets ahead of its natural enemies, you can buy and release more of them. The RHS defines biological control as the use of natural enemies to manage unwanted organisms, usually by introducing predators or pathogenic nematodes. The big advantage: they cause no damage to plants and leave no residues, they are not toxic to people, and pests do not build resistance to them the way they do to chemicals.

• Nematodes, outdoors. These microscopic worms are watered into the soil and move slowly, so they stay where you put them. They are the main biocontrol for soil pests. Slug and vine-weevil nematodes are covered in those specific guides.
• Parasitic wasps and predatory mites, under glass. In a greenhouse or polytunnel, Encarsia formosa controls whitefly, Phytoseiulus persimilis controls red spider mite, and Aphidius controls aphids. The RHS notes these tend to wander off if released outdoors, so they are for enclosed spaces.

Timing and temperature matter. Most biological controls work best between 10 to 30C (50 to 86F), and nematodes keep working in soil down to 5C (41F). Greenhouse predators want at least 21C (70F) in the day, with good light, which in practice means late March or April to September; they often die out over winter and need reintroducing each year.

Intervene by hand, and tolerate the rest

For what is left, the simplest methods are often the best, and they spare the predators a spray would kill. Little and often beats one big effort.

• Squash and pick. The RHS suggests finger and thumb on aphid colonies; Garden Organic suggests picking off heavily infested shoots and dropping them in soapy water. Inspect regularly so you catch problems small.
• Wash them off. A strong jet of water knocks aphids clean off a plant, and many do not climb back.
• Trap. Placed earwig nests, trap boards for slugs and similar simple traps let you remove pests by hand each day.

Then stop. It is normal and healthy to have some pests, and the RHS is clear that they are a vital food source for wildlife. Tolerating a light run of aphids in spring is often the smartest move, because their predators are only just waking up and will clear them for you within a week or two if you leave them to it.

What to avoid

The thing that quietly makes pest problems worse is reaching for a spray. The RHS recommends you do not use pesticides at all, and the reasoning is simple: a broad-spectrum product kills the ladybirds, hoverflies, ground beetles and parasitic wasps along with the pest, so the next outbreak arrives with nothing left to control it. Slug pellets are the same story. Garden Organic warns that non-organic pellets harm the hedgehogs, thrushes and frogs that eat the slugs, taking out your allies as well as your enemy.

In any case, the UK has withdrawn most amateur chemical pesticides from sale, so very few synthetic products are even available to home gardeners now. That is not a loss. It makes the integrated, wildlife-friendly approach on this page the practical default rather than a worthy alternative.

A worked example: aphids

Aphids are the pest every gardener meets, and they show the whole toolkit in one go. They cluster on soft new shoots, especially where a plant has had too much nitrogen, so the first fix is in how you grow: feed for health, not for a flush of sappy growth.

Then let the garden respond. In spring, aphid numbers climb before their enemies are active in enough numbers, so if you wait a while the ladybirds, hoverfly larvae, lacewings, parasitic wasps and blue tits usually give you the control. A bed full of nectar flowers brings those predators in sooner.

Where a plant is being overwhelmed and you want to act now, the gentle options work: squash the colonies with finger and thumb, or blast them off with a jet of water. Under glass you can release Aphidius wasps. What you do not do is spray, because that removes the ladybirds and leaves the aphids, which breed back fastest of all. Tolerate a few, feed the predators, and the balance holds.

For the wider run of leaf spots, wilts, nibbled edges and the like, see our guide to common plant problems.

Frequently asked questions