Companion planting is the careful placement of plants (especially vegetables and herbs) which have been shown to have beneficial effects on one another. Sometimes, this comes down to simple physical reasons – taller plants provide shelter from sun and wind for plants that need protection. Climbing plants can be trained up over taller plants to maximise production in small spaces. Some plants make good companions because their roots grow to different depths, so simply do not compete with each other for water and nutrients.
Plants in the legume family (eg. Peas and beans) promote growth in nearby plants with their nitrogen fixing ability – nodules on the roots enable plants to convert atmospheric nitrogen into a form used by plants. Also they tend to be deep rooted, which promotes aeration of the soil, thus benefiting their neighbours.
The shape of some plants and their flowers can visually confuse insect pests. Other plants, especially herbs, contain strong smelling substances released by their leaves. These scents can swamp odours emitted by other plants and confuse insects seeking out a target.
Still other plants emit chemicals from their roots which can act as growth stimulants for other plants, or can act negatively to retard germination of seeds.
So you see it can get rather complicated! For whatever reason, studies have shown that companion planting really does work. It is unlikely to prove 100% successful in preventing insect attack, but it is just one of the practices used by organic gardeners.
Another trick promoted in permaculture is planting in scattered groupings rather than rows of vegetables in a neat, straight line. This again helps to confuse pests, and can act as an ‘isolation ward’ – one group of plants may be attacked but with a bit of luck the other groups may go undetected! With a straight line of the same plants, pests can simply munch their way across your vegie patch!
So what plants like growing near each other? Some books and charts do tend to give conflicting opinions, but we have compiled a list below of good and bad companions where a general consensus seems to exist!
(References: ‘Companion Planting in Australia ’ by Brenda Little, Reed Books & ‘The Backyard Organic Garden’ by Keith Smith, Lothian Press)
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