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Companion planting

Lavender at Old Moor reserve

Lavender is an excellent plant for attracting insects

Image: Andy Hay

Planting a variety of species and types of plant together has many benefits. It helps to increase biodiversity, improve productivity and takes advantage of the biological control the plants provide for each other. This is known as companion planting.

How does it work?

The main principle behind companion planting is to create a community of plants that provide each other with nutrients and protection from the elements, pests and diseases.

A mix of aromatic, nectar-rich and crop plants grown close together gives a pleasing aesthetic display. The dense planting and mix of species also helps to confuse unwanted insects, while attracting insects that assist with pollination and biological control.

Companion planting works in a number of ways. For example, a 'trap crop' such as nasturtium, when planted alongside cabbage will attract large and small white butterflies to lay their eggs, therefore reducing the damage to the cabbages.

Many plants are attractive to beneficial insects, such as lacewings, ladybirds and hoverflies. By planting these among food crops, the predators control unwanted guests and eliminate the need for pesticides. One of the best species is the widely-available yarrow. This widespread perennial has scented clusters of white flowers, popular with many beneficial predatory insects.

Legumes such as lupins, beans and peas also benefit the garden, as they fix nitrogen from the atmosphere and make it available for other plants in the soil. Some plants also increase or inhibit the productivity of nearby plants. Yarrow, when planted near to aromatic herbs, can increase the production of essential oils. Fennel, on the other hand, is a great insect-attracting plant, but may inhibit the productivity of other plants nearby.

Good insect-deterring plants

The following plants protect food crops by deterring butterflies, moths, flies and beetles from laying their eggs there.

  • Rosemary, lavender and crow garlic
  • Mint, goldenrod and maranth
  • Borage, dill and valerian
  • Clover, sunflower and elderberry
  • Coneflower

Combinations to try

Many combinations of plants are beneficial to one another and have been used in traditional cottage gardens. Research has demonstrated the benefit of this technique, which is has been adopted for use in organic farming farm. Here are some beneficial combinations:

  • Carrots and leek
  • Clover and apple tree
  • Chives and tomatoes
  • Marigold and tomato
  • Geraniums, or lavender and roses
  • Nasturtium and cabbage
  • Maize, beans and squash

Mixes to avoid

The following combinations are best avoided due to incompatibilities of the plants:

  • Onion (Allium family) and peas and beans
  • Dill and carrots
  • Sage and cucumbers
  • Tomato and cabbage family/potatoes
  • Strawberry and cabbage