Organic pest control

Good cultivation is key - plants that are growing in good soil, in good light and that are not allowed to go short of food and water will always grow more healthily than those that are deprived of necessities. Balance is also important. There will be plenty of food for birds, beasts and other invertebrates if you become an organic gardener.

I've been an organic gardener for the best part of 30 years and if anything, I have fewer pest epidemics than I've ever had before. But you'll need patience - a garden that has been run on chemical lines will be imbalanced in terms of natural predators. You'll have to give them a few years to build up, but you'll notice a difference. And as well as having cleaner plants, you'll also be doing your bit to work with nature.

I've been an organic gardener for the best part of 30 years and if anything, I have fewer pest epidemics than I've ever had before

Slugs and snails

The problem: Plants with succulent leaves, such as hostas, seedlings and young plants with soft and sappy foliage are eaten away, and only the midrib is left intact.

The culprits: A wide range of slugs, from the larger brown field slugs that feed above ground to small black keeled slugs that attack potatoes and other roots. On chalky ground, snails are the more common culprits and can demolish plants overnight. In terms of summer bedding, they are particularly fond of tobacco plants.

The solution: The most obvious (and tedious) solution is hand picking. Slugs and snails hate bright sunshine and hot, dry weather, so the best time to find them is at night with a torch. If you have only a few plants in pots, this is an effective means of control. Take the pests somewhere else if you don't want to kill them - but remember, they have a homing instinct, so take them for a car ride.

Copper collars placed around hostas as their buds push through the surface of the soil in spring are effective, as is copper tape around the rim of pots. Half grapefruits, crushed grit and eggshells spread around a plant are rarely a deterrent. Beer traps (empty yoghurt pots sunk into the ground and filled with beer) will catch some slugs and snails, but not all.

Biological control in the form of slug-attacking nematodes can be watered on to kill subterranean slugs, but the earth needs to be have reached a suitable temperature in spring.

Encouraging wildlife - frogs and toads will help with slug control (small ones), as will hedgehogs, and song thrushes feed on snails. In severe cases, look to plants that are resistant to attack, such as those with hairy leaves or tough, leathery foliage. Organic slug pellets, based on ferric phosphate, are available.

Sap-sucking insects

The problem: Plants are weakened, foliage is distorted and bleached, and covered in a sticky honeydew on which thick, black sooty mould thrives. Virus diseases are spread by the mouth parts of pests, which often cluster around the growing point of the plants.

The culprits: Aphids (greenfly and blackfly), whitefly, spider mites, scale insects and mealybugs.

The solutions: Red spider mites can be discouraged by keeping a moist atmosphere in the greenhouse (they prefer warm, dry conditions), and all greenhouse pests can be kept in check by buying predatory insects (biological controls), which vary depending on the pest.

Use sticky plastic traps to trap whitefly. Dab scale insects and mealy bugs with a tiny paintbrush dipped in methylated spirits or whisky. For greenfly and blackfly, use your fingers to rub them off, or spray them with very mild soapy water, or - on sturdy plants such as roses - squirt them with a powerful jet from a hose. Birds, wasps and ladybirds will do their bit, too.

Root-eating larvae

The problem: Plants that looked healthy suddenly wilt and collapse or gradually dwindle in terms of vigour. On inspection, the roots will have been eaten away.

The culprits: Carrot fly will bore into carrot roots (it doesn't always cause the plants to die, but makes the maggoty roots less appetising) and cabbage root fly will eat away the roots of cabbages, which leads to collapse and death. Cyclamen and heucheras are martyrs to vine weevil larvae, which eat the roots and lead to plants collapsing and dying.

The solutions: Position small felt collars around young brassicas when planting to prevent root flies from laying eggs on the soil close to the stems. Sow carrots thinly to avoid needing to thin the seedlings, which releases an aroma that attracts the flies. Sow spring onions alongside them since carrot flies are deterred by the aroma of alliums. Cover carrot rows with crop protection netting.

For vine weevil, check plants' roots at potting time and remove the curly maggots by hand. Water plants with biological control nematodes to keep them healthy. Pick off adult weevils, which feed on leaf edges at night.

Leaf-eating larvae

The problem: Leaves are eaten and shredded, or have rolled downwards and inwards.

The culprits: All manner of larvae of butterflies, caterpillars on brassicas and nasturtium, to tortrix moths and sawfly larvae on roses or fruit trees.

The solutions: Hand picking is the obvious one, but also encourage birds and other natural predators to help by putting up feeders and nest boxes. Crop protection netting will protect brassicas by preventing cabbage white butterflies from laying their eggs on the leaves. Moths that damage apples and pears can be caught in sticky pheromone traps hung in the trees. And remember that wasps eat caterpillars.

Bugs and beetles

The problem: Leaves and flowers are eaten by insects with large mouth parts that chew rather than suck sap.

The culprit: Lily beetles (red adults and grubs covered in black frass) attack leaves and flowers of lilies, earwigs (with pincer-like tails) eat dahlia flowers, and assorted other beetles devour a range of plants, including rosemary, mint and viburnum.

The solutions: Often very difficult, since these pests are tough-coated blighters and quick movers. Trap earwigs in flowerpots that have been inverted on canes among dahlias and stuffed with straw. Lily beetles can be nipped between finger and thumb (if you are quick enough) and their larvae squirted off with a powerful jet from a hose.

Other beetles are more difficult to control, but growing plants that are well fed and not allowed to go short of light and water can make all the difference to their ability to shrug off attacks. Vigilance is helpful in spotting attacks before they get out of hand.

Birds and mammals

The problem: Plants are eaten above or below ground and damage is often rapid and severe, resulting, in some cases, in the complete disappearance of the crop.

The culprits: Mice, squirrels, rabbits, deer, moles and pigeons.

The solutions: These hefty brutes can wipe out a crop overnight. Mice can be trapped humanely but traps need to be reset continuously. Squirrels are almost impossible to control: if they dig up bulbs, lay wire netting above the bulbs and just below soil level, and use squirrel-proof bird feeders.

Rabbits can be excluded with rabbit-proof fencing - wire netting stretched vertically into the earth 45cm below the bottom of garden fences. Deer-proof fencing needs to be at least 2.5m high. Moles can be discouraged with powdered mothballs pushed into their molehills, but if your garden is next to farmland they'll always return and a mole catcher or mole traps may be the only answer.

Use plastic pigeon-proof netting to keep birds off crops such as strawberries. Or make a scarecrow.