Here are some of the different companion planting techniques for different plant requirements.
Nature’s pesticides These are plants that are known to deter pests like aphids, attract pollinators, and release toxins through their roots. The toxins remain in the soil for over a year and kill pest nematodes that can destroy the root system on host plants. Example: marigold (Calendula officinalis) is one of the most popular companion plants to grow for these reasons.
Trap cropping One plant acts as a ‘trap’ to draw pests away from the main crop. Example: grow nasturtiums with roses and lettuces to attract aphids away.
Room to grow Plant beneficial weeds alongside plants that have weak root systems. The weeds naturally ‘till’ the soil, allowing the main crop to send its roots down deeper into the soil. Example: grow clover with tomatoes or corn.
Attract beneficials Grow insectary plants that produce nectar and pollen to attract pollinators like bees, butterflies and hoverflies and the beneficial ladybugs to control aphid pests. Example: fennel, sunflower, lemon balm.
Flavour booster Some herbs can make subtle changes to the flavour of neighbouring plants. Example: interplant basil with your tomatoes and the flavour of both will improve.
Protection and support Some taller, denser plants can provide growing support, shade and shelter for vulnerable plants. By playing to the strengths of the plants’ physical characteristics you can think of ways in which they may benefit the weaknesses of other plants. For example, by choosing plants that are low growing and have large leaves for a living mulch, you are helping to suppress weeds, keeping the soil cool and preventing moisture evaporation while also providing shade for vulnerable roots of plants. Example: grow large-leaved squash with onions.
Strong smells Some plants repel insect pests with their scent. Aroma can also be used to mask the scent of your main crop, effectively hiding them from predators. Example: inter-crop onions and leeks with your carrots to confuse carrot flies.
Soil conditioning This is another way a plant can benefit another, by capturing and releasing nutrients into the soil, making them available to their neighbours. Plants from the Leguminosae family, like clover and beans and peas, fix nitrogen in the soil, making it available to the roots of other plants. Example: mustard (sinapis alba) suppresses soil-borne diseases and conditions the soil. Intercrop clover with your nitrogen-hungry crops, like cabbage.
Choosing a variety of flower shapes will attract a variety of pollinators to your garden.
Pesky aphids ruining your rose blooms or lettuce crops? Lure them away with nasturtiums.
Extract taken from Good Companions by Josie Jeffery, £9.99. Published by Leaping Hare Press - www.leapingharepress.co.uk. - ISBN 978-1-908005-71-7.