Today’s challenge is one of the trickiest - and most important - part of becoming an organic gardener. Discarding chemical pesticides and weedkillers can seem like a step too far for many gardeners, who worry they will not have the time, energy or expertise to protect their plants and keep their gardens tidy.

The problem with these products is that they don’t just wipe out the pests and plants they are intended to target. Their deadly doses also kill beneficial insects, and destroy ecosystems. If you want a seriously unbalanced garden which does not sustain itself, then chemical pesticides will do the trick.

Instead, the organic gardener tries to work with nature, rather than subjecting it to blasts of chemicals. Here’s how you do it.

Cutting out chemicals part 2: put down your pesticides and weedkillers

Keeping on top of pests

Be good: Growing healthy plants and keeping your garden neat, removing rotting vegetation and diseased foliage will go a long way to keeping pests at bay.

Encourage beneficial insects and predators: We’ll have a whole day focused on encouraging wildlife later in the week, but if you have a healthy functioning ecosystem in your garden, you’ll find many pests are kept at bay naturally by insects and animals that eat them.

Here are some beneficial insects you can either encourage or buy in for your garden:

Ladybirds: The larvae of these beetles feed voraciously on aphids and mealybugs. Beware that the larvae look nothing like the shiny neat adult ladybird.
Parasitic wasps: This term comprises many species, including ichneumon, braconid, and chalcid wasps. They develop inside the eggs, larvae or adult bodies of other insects such as aphids, scale insects, whitefly, mealybugs, glasshouse leafhopper and caterpillars.
Frogs: These wonderful amphibians are more likely to rock up in your garden if you have a pond, and will take great delight in slurping down slugs.
Lacewings: The larvae of these gorgeous insects love eating aphids and other small insects.
Hoverflies: The maggot-like larvae of half of the 250 species of hoverfly feed on aphids.
Gall midge larvae: The larvae of the tiny gall midge fly eat aphids.
Nematodes: These tiny creatures can be bought in to deal with specific pests. They enter the body of the pest and infect them with a fatal disease.
Predatory mites: These are used to combat red spider mites in greenhouses. Phytoseiulus persimilis feed on the mites.
Birds: Some birds, especially thrushes, love eating slugs and snails. If you have chickens, they’ll also happily hoover up any slugs.
Hedgehogs: These shy mammals love eating slugs too.
Slow worms: These cool snake-like lizards love hanging out in compost heaps and will eat slugs.
Ground beetles: Shiny and sophisticated, ground beetles will happily eat slugs.

Consider whether you have a regular pest problem that might be solved by buying in natural predators. Plan to order these for the key weeks when these pests become a problem in your garden.

Protect your plants: Keep pests away from your crops and plants altogether with a number of barriers.

A homemade garlic spray will deter slugs from eating foliage. Crush the cloves from two garlic bulbs into a saucepan of boiling water, add chilli powder, and leave to simmer (with the lid on and the windows open) for half an hour. Decant into a spray bottle, and spray all over your plants. This spray also works as an insect repellant for other plants such as roses. Research has shown that slugs hate the scent and taste of garlic oil and will leave their prey well alone.

You can also make a garlic and lemon spray which will kill aphids and repel slugs.

Ingredients
2 large lemons
3 cloves of garlic
1 tablespoon of crushed chillis
1.2 litres of boiling water

1. Grate the zest from the lemons and add to a pan of boiling water, along with the chilli flakes.

2. Slice the lemons thinly and crush the garlic cloves and add to the pan. Cover and simmer for half an hour.

3. Leave to cool and decant into a spray bottle. Spray liberally over plants affected by aphids.

Use physical barriers such as copper tapes around pots to protect from slugs. Or place cloches over plants at their early stages of development to keep out slugs until the leaves are too coarse. You can also get a length of plastic that is three inches wide and coat it in Vaseline, then place as a barrier around your plant as slugs cannot move over Vaseline. Spent coffee grounds dehydrate slugs, while crushed eggshells are too painful for them to move over. There are also Slug Stoppa pellets which dehydrate slugs and prevent them going further towards your plants.

If you are growing fruit trees, place grease barriers on the trunks to stop wingless moths climbing up and infesting the fruit. They should be about six inches wide, and placed on the trunk about 18in above the ground in October.

Keeping on top of diseases

Good management of your garden will go a very long way indeed to preventing serious disease issues that lead to the need for chemical sprays. Here’s how to prevent the problems arising in the first place:

1. Give plants adequate spacing. Check the instructions and plant them with adequate space, not just to grow, but to let the air circulate around them. Overcrowded plants encourage diseases to multiply in the stale air, as well as being weaker specimens as they fight with one another for the light.

2. Clear up dead plant tissue. This is a magnet for diseases and pests. Put it on the compost heap, bearing in mind the instruction in point 3.

3. Do not compost diseased plant material. There are some pathogens which do not die out in compost heaps, or that only die out in extremely hot heaps or when exposed to the winter cold for a sufficient period. It is better to dispose of any plant tissue that you suspect to be diseased by burning it or via your local authority compost collection, as their methods will involve proper hot pile composting.

4. Practise efficient crop rotation. Pests and diseases deprived of their host plants will eventually starve, so rotate crops over a four year period if you can.

There are five main groups of vegetables which require rotating:

Legumes: beans and peas.
Brassica: turnips, swedes, radishes, broccoli, sprouts, cauliflowers, cabbages, kales, rocket.
Potato family: potatoes, aubergines, tomatoes, peppers.
Onion family: onions, garlic, leeks, shallots.
Roots/umbellifers: carrots, celery, parley, parsnip, celeriac.

Pumpkins, salads and sweetcorn can be grown wherever there is space. Grow onions and roots together as the scent of their foliage, grown together, confuses pests from the others.

Here is a sample crop rotation plan:

Year1

Year2

Year3

Year4

5. Don’t buy diseased plants. This sounds rather obvious, but one of the easiest ways to bring disease into your garden is from a garden centre or nursery. Don’t buy plants which are obviously diseased, or which you suspect are ailing. Quarantine any which show symptoms away from the garden.

6. Don’t overfeed plants, especially with nitrogen-rich synthetic fertiliser. You’ll only encourage soft, sappy growth that is susceptible to attack.

7. Employ companion planting methods to ward off pests and strengthen plants against disease. Here is a list of plants reputed work well together:

Alliums – tomatoes, potatoes, cabbage, broccoli, fruit trees.
Asparagus – tomatoes, parsley, basil.
Aubergine – broad beans, marigold, peppers, mints, tarragon.
Beans – spinach, radishes, dill, celery, carrots, broccoli, peas, potatoes, cabbage, rosemary, cucumbers, bay leaves, sage, aubergines and strawberries.
Broccoli - alliums, nasturtium, rosemary, dill, chervil, rhubarb, sage.
Cabbages – celery, beetroot, alliums, dill, potatoes, rosemary, onions, chamomile, hyssop, thyme, sage, chamomile, rhubarb.
Carrots – peas, rosemary, onions, chives, lettuce, sage, beans, tomatoes, leeks, radishes.
Celery – onions, broad beans, nasturtiums, cosmos, snapdragons, tomatoes, garlic, leeks, dill, cabbage, cauliflowers.
Courgette – nasturtium.
Cucumber - sunflowers, peas, radishes, carrots, dill, beets, nasturtiums, chamomile, garlic.
Chives – sunflowers, tomatoes.
Coriander – plant with anything troubled by aphids.
Garlic – plant with anything troubled by aphids, especially roses and raspberries. Also cucumbers, peas, lettuce, rhubarb and celery.
Leeks – apple trees, celery, garlic, onions, carrots.
Lettuce – dill, radish, carrots, beans, cucumber, strawberries, mints, chervil.
Mustard – cabbage, cauliflower, radish, brussels sprouts, turnips, kohlrabi.
Onion – kale, broccoli, tomato, carrot, lettuce, cabbage, chamomile, rhubarb.
Parsnips - peas, potatoes, beans, garlic, radishes.
Peas - carrots, radish, turnip, cucumber, beans, spinach.
Potatoes - horseradish, cabbage, beans, maize, carrot, celery, dead nettle, peas, petunia, onion.
Pumpkin – beans, catmint, radishes, tansy, marigold, nasturtium.
Radish - nasturtium, lettuce, pea, cucumber, chervil.
Rhubarb – cabbage, borccoli, beans, columbine, garlic, onions,
Strawberry – lettuce, broad beans, onion, spinach, caraway, borage, thyme.
Tomatoes – nasturtiums, marigolds, basil, onions, roses, asparagus, peppers, oregano, parsley, carrots, petunias, carrot, cucumber, mint, borage, alliums, pelargoniums.

Organic approaches to disease

If disease does strike, you can remove the offending plant, or at least the visibly diseased section of it, as soon as possible to prevent it spreading. Or you can employ the following organic methods to combat the disease.

Plant oils: e.g neem oil can combat diseases such as powdery mildew and pests.

Sulphur: Acts as a fungicide against mildew, black spot and grey mould.

A number of sprays and powders previously accepted as organic have since been withdrawn, including derris and bordeaux mixture.

Are you caring for your plants properly? Have a look at how you have planted perennials in your garden and move them if necessary. Plan to space your vegetables properly this year.

Keeping on top of weeds

A lot of gardeners give up being organic when they find themselves faced with a garden full of weeds. For some serious infestations such as Japanese Knotweed, chemicals must be used and will be less damaging to the environment than the plant itself. But in many cases, it is simply a case of knuckling down and managing serious weeds at the source by removing their roots from the soil and continually removing new growth.

Here is a gallery of the most common weeds, along with instructions on how to control them:

As a general rule, clearing soil full of weeds is very hard work, but it is worth investing a large amount of initial time and effort to eradicate them from your plot so that they do not recur profusely year after year.

As you’ll have seen from the gallery above, perennial weeds don’t just reproduce from seeds. Often they will propagate themselves from the smallest fragment of root, which means that easy fixes like rotovators will actually be the most expensive mistake you’ll ever make.

The best way to clear a plot of weeds is firstly to dig through the soil to the depth of at least a foot and remove the roots by hand. Don’t put the roots on your compost heap: burn them or leave them to soak in a bucket of water for a few months before doing anything with them to ensure you don’t return them to the soil.

Once you’ve dug all the roots you can find, cover the soil with black plastic sheeting, thick cardboard or another impermeable cover. Cover the soil for as long as you can do without it: a year if possible, and you’ll find that emerging weeds will have significantly died back when you start growing.

For weeds in tricky spots, pour a kettleful of boiling water over them, and this will kill them all the way to their roots.

Think seriously about how to eradicate the perennial weeds that are clogging up your plot. If you can, cover as much of it as possible. Set aside a couple of weekends in your diary where you can dig and remove the roots: autumn is a good time when the ground is soft and growth is still obvious.

That’s it for today. If you haven’t already, don’t forget to subscribe to our emails for this course. Tomorrow we’ll be looking at the plants you can grow to encourage wildlife to your garden.