Companion planting guide
Companion planting is a method of planting different plants together so one plant can improve the growth of another. This is achieved by using a plant with strong defenses to boost the weakness found in other plants, or by attracting the pests away form the main crop.
Some plants produce scents or chemicals to protect themselves from pests, these can be useful if placed next to a plant that cannot defend itself from a pest attracted by it's own scent. A good example of this would be the Carrot, and the Carrot Root Fly. The Carrot Fly is attracted to the smell of the Carrots especially when you are thinning the crop out. The scent of Carrots is strongest when the leaves are crushed during thinning. So to stop the Root Fly from finding the Carrots place a smellier plant near the Carrots.. There are various plants that can achieve this, Onions are a good example. The strong odour given off by the Onions will mask the scent of the Carrots.
Use a 'Honey pot'
If the plant to be protected does not give off a scent, or the pest isattracted using another means you could look to use a sacrificial plant to become the victim rather than the crop you are trying to grow. Slugs love Lettuce, but they love Marigolds even more, so use Marigolds as a border to any bed where slugs can be a problem.
Marigolds are also very good at attracting Hoverflys, and Hoverfly Larvae like to eat Aphids, in fact your average Hoverfly Larvae will eat around 800 Aphids before it pupates. Ladybirds are also very good at eating Aphids so attract them with plants like Dill and Fennel.
How about repelling the pests? Use plants like Tansy to get rid of Ants. I was trying to find a use for Tansy last month as I had a good crop of it in the front garden. After a bit of searching it turns out this is an ideal solution for repelling Ants, although it should be noted Tansy can be quite invasive, and you may want to keep it in a pot. I returned to the patch of Tansy in my garden and took the picture on the right of hundreds of Ants 'Milking'' Aphids on the stem. I think my Ants are immune to the effects of Tansy?
Just as there are good companion planting combinations, there are also bad combinations. Some plants will actually restrict the growth of other plants either by competing for nutrition in the same way, or by excluding incompatible odour's, scents or chemicals. Below is a list of plants that should not be put together.
Companion planting is not restricted to removing the threat of pests, there are also other benefits gained by using certain plants. Peas will build up nodules of Nitrogen on there roots, and when the plant has died the Nitrogen is left to enrich your soil. On and even more subtle level than this Green Manure or even Leaf Mould can also be looked at as a form of Companion Planting. For more information on plants and their companions use the Plant Selector on the right.
As you can see from the Tansy picture, although companion planting is based on tried and tested solutions, there is no guarantee that it will be successful, maybe there are some plants you have found to be good, or bad, companions to your crops. Why don't you use the feedback form to post your companion planting successes or failures, we will add them to the database and hopefully build a definitive reference.Happy companion planting...