A guide to
Companion planting

Companion planting is a system of planting different crops next to each other for the benefit of one or both plants. It’s a well-established gardening practice, and one that works in many different ways.

Here are a few of the ways that companion planting can be used to benefit plants:

• to deter pests, to attract pest predators, or to lure pests away from a crop without the use of chemicals
• to attract pollinators
• to provide a screen or shelter for plants
• to help smother weeds
• to maximise the use of growing space
• to increase the nutrients available in the soil

As well as benefiting plants, companion planting can make your vegetable garden look great too, with flowering plants adding colour and scent.

Nasturtiums attract aphids away from crops such as beans, courgettes and cucumbers. They also lure egg-laying white butterflies away from cabbages and other brassicas, reducing the risk of infestations of cabbage white caterpillars on these plants.

French Marigolds (Tagetes) have a smell that deters whitefly, so they’re good to plant near Tomatoes.

Aromatic herbs deter many insects. Lavender and rosemary are particularly good at this, and there’s the added benefit that their flowers attract pollinators. Mint, chives, dill and garlic are great at deterring flies and beetles from attacking crops such as carrots, brassicas, onions and radishes.  They’re also useful near aphid-prone flowering plants, such as roses.

NB: It’s best to grow mint in a pot, not in the ground, as it spreads easily by underground runners and can take over a garden.

Leeks and carrots are a good example of companion planting that benefits both partners. Leeks planted near carrots can help deter carrot fly by masking the scent of the carrots, whilst the carrots will help keep leek moths away from the leeks.

Achillea (yarrow) is an example of a plant that attracts beneficial, predatory insects. These include lacewings, hoverflies and of course ladybirds, which all eat aphids.

Berry-bearing trees and shrubs like rowan and pyracantha will help attract birds, which eat insects. Blackbirds and song thrushes will eat slugs and snails too, helping to keep these pests under control.

We all know the importance of having a healthy population of bees (of which there are many species) but there are many other insects such as hoverflies and butterflies that also act as pollinators. These are of course vital in crop production, and the RHS provides lists of plants for pollinators on their website.

The RHS list of pollinator-friendly garden plants is arranged by season, helping us to encourage different types of pollinators into the garden over a long period, and wildflowers are arranged by the type of ground and garden area. Plant labels, websites and catalogues often carry the RHS Plants for Pollinators bee logo, making it easy to choose the right plants.

A few of the most popular plants for pollinators include:

• Borage
• Lavender
• Cosmos
• Ivy
• Erysimum (wallflowers)

An attractive example of beneficial companion planting is to combine runner beans with sweet peas. English marigolds (Calendula) are also great pollinator-attractors, ideal for planting near vegetables such as courgettes.

Taller crops, especially sweetcorn but also peas, provide a useful windbreak in exposed areas, protecting other, less robust plants especially while they are getting established. The shade these plants provide can also be useful to reduce the risk of bolting in crops such as lettuce and spinach.

These two aspects of companion planting can often be considered together. For instance, faster-growing crops like lettuces, beetroot, baby carrots, radishes and some herbs can be sown or planted in the space between rows of slower growing vegetables like brassicas and parsnips.

By covering the soil, these faster-growing crops help to keep weeds at bay – a valuable task, as weeds can attract unwanted insects, spread disease and take nutrients. The fast-growing crops also provide an extra (‘catch’) crop, making use of space in the garden that would otherwise be unproductive.

Legumes, such as peas and beans, and also Lupins, fix atmospheric nitrogen in the soil, making it available as a nutrient for other crops. Nitrogen is essential for healthy plant growth, especially for leafy plants such as Spinach and Kale.

Some plant combinations aren’t recommended. This may be because:

• both plants may compete for the same nutrients
• one plant may release chemicals that inhibits the growth of the other
• one plant may attract pests that affect the other.

Not all sources seem to agree on everything, but there does seem to be general consensus on not planting the following combinations:

• Tomatoes with cabbages or potatoes
• Tomatoes with sweetcorn
• Carrots with dill
• Cabbages with strawberries
• Peas or beans with onions.

Combinations that work well in one garden may perform differently in another, so keep notes of what you have sown and where, learn from what works well, and what doesn’t, and share your experiences.