This isn’t quite true though because just like us they like to pick and choose who they hang around with. Each of the plants competing for space, light, air, moisture and nutrients. They all want their little bit of personal space. Some plants will release toxins through their roots straight into the soil and these act as natural growth inhibitors to control competing plants. Another example are rhododendrons and laurel that contain a plant toxin in their leaves. As their fallen leaves break down they release a natural herbicide over the immediate root area to suppress other plants.
All of this activity is to ensure that the various species have a better chance of survival. If we think of these as bad companions in the garden we have to make sure that we keep them apart.
Companion planting is the practise of growing of two or more compatible species of plants close together; either to their mutual benefit or as is more usual to the benefit of the dominant crop. In the flower garden it could be a prized tree, shrub or herbaceous perennial but in vegetable garden this of course means the plants that we eventually want to eat. The principles behind companion planting are quite straightforward.
· They involve growing plants that will attract beneficial predators such as ladybirds, hoverflies, and lacewings into the garden to lay their eggs on a host plant and the emerging young can feed on any aphids on the nearby main crop. The poached egg plant, Limnanthes douglasii is very effective at doing this.
thTThere are plants that secrete unpleasant (but harmless to humans) toxins through their roots to control soil borne pests and diseases. Members of the dwarf marigold family can be interplanted amongst the main crops to control harmful soil nematodes such as wire worms.
· Plants that produce strong scents that confuse and distract the pests by masking the scent of the main crop. A traditional combination is growing basil or dwarf tagetes amongst tomato plants to confuse whitefly.
· Plants that can “lock” beneficial nutrients in the soil to the benefit the main crop. For example peas and beans produce nitrogen fixing nodules on their roots that will benefit any leafy crop e.g. lettuce being grown close to them. A nitrogen hungry crop e.g. cabbages can be planted on top of the roots of the pea or bean crop after it has finished cropping and the haulms have been cut down.
· Plants that are used as sacrificial plants to attract pests to lay their eggs on them so that we can gather the eggs or caterpillars and destroy them. An example of this is growing nasturtiums between brassicas to attract cabbage white butterflies away from the main brassica crops.
· Plants that can be used to control invasive weeds; one example is growing Tagetes minuta which has displayed some control over ground elder and convolvulus (bindweed). Again the roots secrete toxins that are poisonous to the plants that need to be suppressed.
The classic example of companion planting is “The Three Sisters” which is a combination of Sweet corn, climbing French beans and squashes or pumpkins
The tall, rigid growing sweet corn is interplanted with climbing French beans that use the corn as a support and both of them are underplanted with squash/pumpkin to shade the soil to keep their roots cool and to conserve moisture. And of course the nitrogen fixing roots of the climbing bean feeds the corn and the squashes. You could substitute courgettes for squash/pumpkins if you wanted to.
Nearly all of the plants that work in companion planting are either hardy or half hardy annuals that you can grow quite easily yourself from seed. We are looking at candytufts, calendula/pot marigolds, dwarf marigolds, echiums, nasturtiums, rudbeckias, all straightforward to grow. One plant I have noticed that is irresistible to hoverflies is beetroot when it is flowering. I save my own seed and I always leave save one cultivar of beetroot to run to seed in its second year. And when I do it is always surrounded by a shimmer of hoverfly wings all beating as one.
We should try to take advantage of every opportunity to that nature provides us with. It isn’t a case of being muck and mystery but applying the same principles that occur naturally in the plant world and using them to our own advantage and importantly to support the ecology of our organic gardens.