What is companion planting?

If you spend time out in your garden you get to know which plants appear to grow well together. But some gardeners actually deliberately plant certain things together to allow one plant to benefit from another. Sometimes it’s a virtually unseen benefit where one plant may deter a pest from attacking another, while others may just improve the soil health around your plants.

It’s called companion planting and if you’ve never heard of it, it’s well worth learning a bit more.

Good pollination

In order to get a good harvest from many crops you need pollinating insects in your garden. This is particularly true for runner beans that need the lovely bumblebees to force their way into their intricate flowers and move the pollen from flower to flower. The runner bean flowers themselves do attract bumblebees with their nectar rich flowers, but if you grow a wider variety of flower shapes and lots more of them then the bumblebees and other pollinators will have a better reason to visit your plot and pollinate your crops. Plant Phacelia, borage, pot marigolds, nasturtiums and other pollinator friendly plants around and within your veg patch to attract the pollinators.

Decoy plants

Some plants are a magnet for certain insects. Cabbages, kales and other brassicas in summer are the food plant of a common butterfly but and can be quickly devoured by their caterpillars. Wasps, birds and other garden predators will take these grubs to feed for their young, but sometimes the cabbages are reduced to lacy leaves with not much left for us. Plant a generous row of nasturtiums along one edge of your plot.

These can act as a decoy for adult white butterflies looking for food plants for their babes. They lay their eggs on the leaves of the nasturtiums instead of your kale.

Mask the scent

Many insects use scent to find a mate and food. You can mask a favourite host plant of one insect by planting something pungent nearby to disguise the smell. The carrot fly adults seek out your carrot crop to lay their eggs. When these hatch the developing larvae carve deep tunnels in the sweet roots making them virtually inedible. Plant your onion crop alongside the carrots to disguise the carroty scent. Sow the carrot seed between the developing onions to confuse the adult carrot flies and stop them laying their eggs.

Avoid thinning the carrot crop as this releases smells that attract the carrot fly.

Deter the pests

Some plants exude chemicals and smells that deter some insects. A better-known example of this is a type of marigold (tagetes) that repels soil nematodes. Useful to protect some plants but may also affect the beneficial nematodes that some gardeners use to control certain garden pests like vine weevil and slugs.

French marigolds are a good companion plant for greenhouse tomatoes as the smell discourages greenhouse whitefly, which can be a real problem in glasshouses and polytunnels. Plant them along side for the best results and interplant with plants to attract bumblebees as these pollinators are the best for tomatoes and will help ensure a good crop.

Attract predators

We all want to harness the power of nature in our gardens and what better way to do that than to grow plants that attract predatory insects. If that sounds too scary, let me explain. The natural balance in the garden and wider environment is kept healthy by natural predation of insects, some of which we regard as pests. Many insects predate on others, thus reducing their effect in the garden. Hoverflies for example feed on aphids, their larvae have a huge appetite for these sap sucking beasties that would otherwise attack the soft growth of our plants. So it makes sense to grow plants with flowers that attract these garden allies to increase your share of these beneficial predators in your garden.

Hoverflies have short tongues so they need accessible flowers where they can drink nectar. Umbellifers (now renamed as Apiaceae) such as fennel, astrantia, angelica, orlaya grandiflora (white laceflower), wild carrot and Ammi majus (Bishop’s flower), are a great choice and will attract all manner of lightweight dainty insects that feed on their multiple flowers and copious nectar. Plant these around your garden to provide sustenance for adult hoverflies and encourage them to breed on your plot.