Mixing flowers, herbs and vegetable crops in the same space is good for biodiversity, but it also lessens the chance of serious outbreaks of pests and disease. Clare Foster demystifies the art of companion planting, a term used to describe the practice of growing different food crops and flowers together in symbiotic harmony
Flowers such as marigolds being grown as companion plants among the vegetables in Tom Hoblyn's Suffolk garden
As an organic practice, companion planting can be taken very seriously, but it can also be as simple as planting a few marigolds around the edges of your vegetable beds. In fact many people are companion planting without realizing it, by introducing a mixture of flowers, fruit and vegetables into their gardens. But by giving a little more thought to the practice, and using some tried and tested combinations, you may find your plants are much healthier, and with better yields, as a result.
Humans have been companion planting for thousands of years. North American Indians historically planted squash, beans and corn together in a triumvirate known as the ‘three sisters’. The beans brought valuable nitrogen into the soil, while the corn stems provided structure for the beans to climb, and the squash provided a living mulch later on in the season by shading the soil with their broad leaves, reducing evaporation and suppressing weeds. In France, roses are traditionally planted at the end of vine rows. Designed as an early warning system for the farmers, they attract aphids before they reach the vines, as well as highlighting any fungal disease like mildew before it takes hold on the vines.
The theory of companion planting works both above and below ground. Above, bright flowers can attract beneficial insects and pollinators or divert insect pests away from vegetable crops, while aromatic foliage can repel the pests. Below the surface of the soil, the range of different root systems that exist in a polycultural environment can also be beneficial, with some plants’ roots spreading wide to improve the soil structure, and others reaching deeper down to bring nutrients up to the surface. Some crops, in particular leguminous plants such as peas and beans, ‘fix’ nitrogen from the air and draw it down into the soil to be made available to other plants. And finally, the risk of soil-borne disease is lessened if you have more than one type of plant in a single bed.
There are endless recommendations for companion planting combinations, most of which have not been tested scientifically, but here are the ones that seem to work best.
Marigolds and Leaf Veg
Growing marigolds among vegetables such as kale, calabrese and lettuces will attract beneficial insects such as hoverflies, ladybirds and lacewings, which are all natural predators of aphids. Hoverflies are attracted to the colour orange, so you could also try Californian poppies, tagetes or the poached egg plant.
Nasturtiums and Brassicas
Like marigolds, nasturtiums are super-easy to grow from seed and will spread rampantly to cover any bare soil. These plants are full of mustard oil which will attract various pests including cabbage-eating caterpillars, so they can be used as a sacrificial plant for your more precious crops of broccoli, cabbage or kale.
Hyssop and Brassicas
A member of the mint family, hyssop is thought to attract the Cabbage White butterfly away from brassicas. Its dark blue flowers are also magnets for bees.
Basil and Tomatoes
These two plants work as well in the garden as they do on the plate. Growing pots of basil in the greenhouse will attract whitefly away from the tomatoes, and their aromatic leaves will repel other pests. They need the same growing conditions, with plenty of heat and water.
Tagetes and Potatoes
The roots of tagetes exude a chemical that is repellant to soil pests such as eelworm, so it works excellently with potatoes. It can have the same effect with weeds such as bindweed and ground elder.
Lavender and Leeks
Lavender or oregano can be used as a companion plant for leeks and carrots as the aromatic leaves can deter aphids and other pests such as Allium leaf miner.
Borage and Broad Beans
Broad beans can often be swamped by blackfly, but the pretty blue flowers of the borage will attract pollinating insects including hoverflies, whose larvae will feast on the blackfly.
Dwarf French Beans and Kale
The kale will benefit from the nitrogen that the beans draw into the soil, and in turn the kale will provide sturdy support for the beans with their more sprawling habit.
Thyme and Roses
The strong scent of thyme can deter blackfly, making it a good companion for roses. A tea made by soaking thyme leaves in water can be used to spray cabbages against whitefly.
This story originally appeared in House & Garden UK.
