A number of plants can be grown together to help reduce attack by pest and disease. It may be necessary to experiment over a number of seasons to obtain the optimum vegetable planting companion planting density to provide some protection.
Growing Onions, Leeks and Carrots together will confuse the Carrot Fly and Onion Fly reducing the damage caused by these pests. One of the most common pests found in the garden are the many types of Aphid.
The larvae of the Hoverfly will eat large quantities of Aphid and to encourage Hoverflies into the garden grow Convolvulus Minor and Limnanthes Douglasii (Poached Egg Flower).
Growing Basil, Chilli Peppers and French Marigolds amongst Tomatoes will help to reduce pest attacks. In the greenhouse Whitefly is a very troublesome pest of Tomatoes and growing French Marigolds by the door and near ventilators is said to be beneficial.
Inter-planting brassicas with Dwarf French Bean and French Marigold will help to reduce pest attacks.
Planting Chives or other members of the Allium family will reduce attack on the fruit from Scab and other fungal diseases. Onions can also help prevent mould on Strawberries and Summer Savory will reduce disease problems in Beans.