Companion planting works on the premise that planting certain things together will free one or the other plant from pests, or boost productivity. Scent and sacrifice play a big part in this equation. The strong scent of one plant can help prevent pests homing in on another which you consider more valuable.

What you plant with your crops can have a significant impact on your harvest. So, how can we reap the richest rewards?

:: French and runner beans: Grow sweet peas to climb up wigwams and other stakes among your bean plants and you should do well. Pollinating insects will be attracted to the sweet pea flowers and are then likely to pollinate your beans, plus they'll make the area look prettier.

:: Cabbages: Mix your cabbages with French bean plants, nasturtiums or Shungiku, the edible chrysanthemum, which can reduce attacks by caterpillars.

:: Greenhouse companions: French marigolds (Tagetes patula) deter whitefly from visiting your greenhouse. Plant a few under tomatoes to keep them at bay. Plant basil next to tomatoes to keep the aphids off, although they will go for the basil. Nicotiana will attract whitefly, keeping them off other plants.

:: Herbs and nettles: Almost all aromatic herbs are generally beneficial, as their smells confuse pests. Chamomile is thought to be good for healing sick plants. Nettles are reckoned to be good for neighbouring plants and increase the volatile oils in such plants as valerian, mint, sage and rosemary, so the potency of many plants increases measurably when planted near nettles. Summer savory, a strong herb, has been planted next to broad beans to protect them from black bean aphids.

:: Hyssop: Plant strong-scented hyssop among brassicas to ward off cabbage white butterflies. Artemisia is also effective for this, preferably in a sheltered spot so the wind doesn't carry the strong smell away.

:: Mint: If you have an ant infestation in your greenhouse, tear off a bunch of mint and place it where the ants are congregating. They should disappear fast, but replace the bunches of mint every couple of days to ensure they don't return.

:: Use tall plants such as sweetcorn or peas to provide shade for crops that are prone to bolting, such as lettuce, coriander and spinach.

:: Leeks: Pungent crops such as leeks, garlic and chives can confuse insects including carrot flies, onion flies and leek moths, so plant them with carrots if you want to stop carrot fly ruining your crops. When leeks and carrots are planted together, their scents act as repellents for each other's pests.

:: Nasturtiums: These pretty annuals secrete a mustard oil that insects love. Use them as a sacrificial crop to save your brassicas, while in the greenhouse they'll protect your tomatoes and cucumbers from whitefly.

:: Pot marigolds: You can reap much greater harvests by planting annuals which are attractive to pollinating insects close to your fruiting vegetables such as courgettes, beans and tomatoes. Sow them in autumn to overwinter and they should flower in time to attract insects in early summer, which will boost your harvest.

:: Radishes: These fast-growing roots can be grown effectively with carrots. Plant them at the same time and the radish seeds will germinate ahead of the carrot seeds, loosening the soil for the germinating carrots. When you harvest the radishes a few weeks later, the carrots will still be young but will then have more space to grow.

:: Plant garlic among roses to ward off aphids