Plants sometimes behave in a similar way to people, falling out with one, getting along and building a friendship with another.
It's been going on for a very long time, thousands if not millions of years. It was the Greeks and Romans who probably paid the most attention to the varying levels of interaction between certain groups of plants and there's been a constant battle over the years to prove that such a theory exists.
Rooted firmly in ancient and not so ancient folklore more than in modern science, companion planting can be of immense value to any garden; bringing in and maintaining larger populations of predators and pollinators, keeping pests and diseases away, creating shade or providing nutrients. While some of the ideas seem ridiculous, there is still much to be understood, but general principals have been long established.
Understanding how plants interact with each other and the insects around them is the key to how companion planting works. It simply means carefully choosing which plants to grow with, following or preceding crops, or growing plants nearby that are known to "get on" with each other or offer a particular benefit to assist the growing of others. It also means being aware and not planting known enemies together! This is accepted as an organic way of growing.
Plants that enjoy similar conditions naturally occur together. Their success while growing in the wild boils down to the interactions with other plants situated around them.
In the veg garden, crop rotation is important and forms part of the understanding of companion planting. Growing the same crop on the same piece of ground year after year is asking for trouble; pests and diseases build up and the ground will become depleted of certain nutrients. The once-thrifty and healthy crop becomes a miserable failure; so moving crops around has to be carried out.
Understanding which plant belongs to whose family will be helpful. There are some surprises – radishes, for instance, are in the brassica family and related to sprouts!
Although plants compete with each other, they are often not after the same riches. In a way, this allows more plants to be planted in a given area without them choking their neighbours. Some low-growing, shallow-rooting ground-cover plants can exist in the light shade of deeper rooted trees, while climbers can grow up the trees and create a three-tier effect. If the trees are well spaced, shrubs can be incorporated into the area, thus creating a fourth tier. These can provide a rich habitat for wildlife; using the soil in such an efficient way gives weeds less opportunity to grow.
Strong-smelling plants such as onions or leeks can confuse pests when planted among crops that are susceptible to damage. Take the carrot fly, for instance – they are only small but they can smell carrots from some distance away. Planting onions or leeks within the row or alongside will disguise the smell of the carrots and deter them.
French or African marigolds are also considered to be a pest deterrent. The foliage gives off a strong pungent scent which discourages whitefly and other non-desirables. Their roots keep soil free from nematodes.
Lavender has a strong scent which is reputed to repel moths and fleas! Plant lavender bushes under and around fruit trees to discourage codling moth; hang sprigs of dried lavender in the trees during May to repel them. Lavender can also be used to under-plant around rose bushes to repel aphids.
Plants from the Leguminosae (legumes) family, which include peas, beans, sweet peas, clover, lupins etc have the ability to "fix" atmospheric nitrogen (nitrogen produces leafy growth) for their own use and can create a fertility surplus to help feed plants that are growing around them. They have nodules on their roots and stems where the nitrogen is stored. Once the plants have finished cropping they can be dug back into the soil where, as the plant matter decomposes, nitrogen is returned to the soil ready for use by the following crop.
Green manures work in the same way and are very beneficial to the soil. Some are sown during the autumn and dug into the soil in the spring – others are sown in the spring and dug in later in the year. Some flower and attract beneficial insects while others reach deep down into the erth and collect minerals. Once they have grown, they are dug back into the soil where they increase the organic matter content and release their nutrients.
Traditionally, orchards were furnished with grass. Clover was added to boost the nitrogen with alfalfa to access deeply buried minerals. As grass competes with trees for nutrients and water, "grassing down" was a practice used around over-vigorous trees, pears in particular, to help curtail their growth.
When planting fruit trees in a grass area, always make certain there is a clear circle around the tree and make sure that it is kept free from grass, which has a habit of sneaking back in when you're not looking! It is said that grass roots have a "breath" that shrivels the tender root tips of the tree – another good reason for keeping the grass away from the trunk.
Clumps of chives grown around the tree will inhibit the formation of apple scab but don't plant apple trees near the potato patch as the potatoes are sure to go down with blight. Planting broad beans, however, will inhibit the pests that attack potatoes, and vice versa. All beans seem to grow well near carrots, cabbage, lettuce, peas, parsley and cauliflower; but will grow badly when grown near onions, garlic fennel or gladioli!
Take care when planting garlic as it can taint the flavour of peas, beans and some cabbages.
Bees do a great job in pollinating flowers and help gardeners to produce good crops of fruit and veg. Attracting them to the gardens makes good sense. They really love lavenders, hyssop, savory, caryopteris, sedum, sweet alyssum, clover and even dandelions!
Other beneficial insects include ladybirds that in both larvae and adult stages of life have voracious appetites, especially for aphids. They hibernate during the winter in sheltered places under leaf litter or among dense vegetation. Wasps are normally annoying and associated with attacking and ruining fruit; but during the early part of the year they kill insects such as aphids and caterpillars, which they feed to their young.
Hoverflies look like wasps and are so called as they "hover" either when feeding or when in flight; as adults they feed on pollen and nectar produced on "flat" daisy-type flowers, and are therefore important as pollinators. Their larvae feed happily on aphids.
It's lovely to see butterflies fluttering by in the garden; but the cabbage white is an unwelcome sight in the veg patch. It doesn't take them long to find the cabbages to lay their eggs upon. The larvae (caterpillars) soon hatch and consume the leaves at an alarming rate. Picking off the caterpillars and destroying them is an option. Cabbage whites are also particularly fond of nasturtiums and mignonette which can be planted alongside to lure them away from the cabbages!
Companion planting can be utilised to create a very happy family in your garden!