Companion planting is an effective way to protect plants from the unwanted effects of pests and diseases. A number of plants give off strong odours that can confuse the olfactory senses of the insects. Many herbs are useful for this purpose, including basil, lavender, rosemary, rue, thyme, chives and garlic. For them to be effective, you should plant them throughout the garden.
However, companion planting is much wider in scope than just confusing an insect’s sense of smell. In its broader sense, it includes any plant that is beneficial in some way to another plant. Think of companion plants as being ” good neighbour”.
It may be a simple matter of one plant shading another or modifying the humidity. One plant’s roots might aerate the soil, or help drain excess water. Some plants can protect others as much as themselves by virtue of defence mechanisms such as thorns and stinging hairs or, by producing compounds that are poisonous to insects and pests. Other plants offer benefits to their neighbours by attracting or housing desirable insect predators or by exuding odours that attract pollinators.
Benefits of Marigolds
Nematodes (eelworms) cause reduced growth, low yields and wilting in a variety of vegetable crops. When infected plant roots are dug up, the appear to have tiny gall-like growths over the surface. However, the nature has produced a powerful nematicide, a bi-molecule produced to some degree in the roots of all species of marigolds (Tagetes spp). The dwarf marigold (Tagetes patula) is particularly useful for barrier plantings around gardens.
Some plants are particularly attractive to pests , either because of their colour, smell or taste, and thereby protect other plants from attack. Bright yellow nasturtiums attract aphids away from cabbages. Zinnias have long been used as trap plants to lure Japanese beetle. The trap plants might not be sufficient protection for your garden, but they do contribute towards maintaining healthy crops.
- Basil with tomatoes, asparagus, beans, grapes, apricots and fuchsias
- Beans with potatoes and sweet corn
- Chives with carrots, cucumbers and tomatoes
- Cucumbers with potatoes
- French marigolds with tomatoes, roses, potatoes and beans
- Hyssop with cabbages and grapes
- Leeks with celery
- Lettuce with carrots, onions and strawberries
- Melons with sweet corn
- Mint with cabbages and other brassicas and peas
- Nasturtiums with cucumber, zucchini, squash and apple trees
- Onions with carrots, kohlarbi and turnips
Peas with carrots
- Apples with potatoes
- Beans with garlic
- Cabbages with strawberries
- Gladioli with strawberries, beans and peas
- Sunflower with any vegetable but squash
- Wormwood with almost everything