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Organic Gardening
Companion Planting

We have all heard the line that 'roses love garlic', possibly the most famous of all companion planting associations.

Companion Planting is based on the premise that plants have such likes and dislikes about their neighbours. Also that particular plants can reduce the incidence of pests in the garden.

If 'Roses love garlic'? Why not try chives?

If 'Roses love garlic'? Why not try chives?
Some theories about companion planting have been established, and others have had less startling success in scientific trials.

Overall, few cases of beneficial companion planting have been researched well enough to demonstrate true advantages. The lovely little Tagetes patula, or French marigold (actually from Mexico), and its cousins Calendula, have been shown to be invaluable in companion planting.

Using mixed plantings in the garden is likely to be beneficial simply because they bring greater balance and a diversity of plants and species, that, in turn, attracts pest predators and avoids the pest-ridden effects of monoculture.

Monoculture is the planting of rows and rows of the same plants- fields of lettuce, corn and onions, for instance, paradise for a pest or disease that, once introduced, can simply move from plant to plant. Monoculture does not encourage a healthy mixed population of creatures - essential in an organic garden.

Companion Planting or Simply Mixed Planting?
Removing some of the traditional barriers and divisions in the garden will help to develop and maintain a healthy mixed population of creatures, and thus your garden's health.

'Tagetes patula',
Tagetes patula, 'French' marigolds come from Mexico

Some pests are attracted to plant flowers and by mixing flowers and vegetables together you can protect them. Garlic with roses will control greenfly and savory with peas has not proved to be as effective. Ladybirds and lacewings are insect predators that can be can be encouraged by providing a range of species.

Poppies, and nastursiums planted between plants are said to minimize aphids; daisies such as asters to attract flying insects, and most are tough, easy plants.

Nepeta (catmint) is a great plant for smothering weeds; plant it and lavender to attract many summer flying insects. If you don't own a cat, however, growing nepeta may make your garden a magnet for other cats.

Praying Mantis, one of the good guys
Praying Mantis, one of the good guys

Espaliered fruit trees within your vegetable garden and mixing flowers amongst the rows will help. Or grow your salad vegetables in the ornamental garden, for example, 'lollo rosso' lettuce with their wavy, coloured leaves, spinach, ruby chard, courgettes and other plants can make a contribution to the border.

Growing vegetables, fruit and ornamentals together requires more effort and attention to ensure that plants are not swamped (or swamping their neighbours!) and filling the gaps as you harvest your vegetables. It is not any more work than a traditional herbaceous border where the work of trimming, deadheading, cutting back and filling gaps continues throughout the growing season.

  • Onions and carrotfly It is argued that carrotfly is attracted by smell and that planting carrots between rows of strong-smelling onions will disguise the carrots. However you need four rows of onions to one of carrots for there to be a real benefit. Once the onion leaves stop growing and the onion bulb begins to form, the benefit goes.
  • Beans and Brassicas Brassicas interplanted in alternate rows with unrelated crops (e.g. dwarf beans) will have a reduced pest level (e.g. aphid). But the plants need to be a similar size when planted, grown about 25cm apart (10") and the gaps between the plants filled as quickly as possible. To do this both need to be raised in pots and planted out together.
  • Tagetes The lovely little tagetes, or French marigold, however, is invaluable in companion planting. Cabbage white butterfly are attracted to their host plant by smell and planting rows of tagetes is effective in masking the smell and reducing cabbage moth damage. A secretion from the roots of the Mexican tagetes deters eelworms and your potatoes and tomatoes are left alone.
    Tagetes are also said to kill couch grass, and certainly this is a far prettier solution than the ubiquitous sprays!
    Tagetes and calendula marigolds planted near tomatoes and roses will reduce aphid attack as the marigolds will attract the hoverflies that are voracious eaters of these pests.

White butterfly - the scourge of green vegetables
White butterfly - the scourge of green vegetables
Practising crop rotation, which advocates rotating crops to reduce a build up of soil borne diseases, is more difficult when crops are intermingled, but it is still possible to track and rotate crops, and the benefit in reduced pest levels and avoiding pesticides is certainly worth it.

The change in gardening also requires a mental shift- from regimented rows and bare earth to a more mixed look, with flowers and vegetables grown in a more relaxed manner.

Aesthetics aside, companion planting does seem to work in some cases and not others. Science has yet to establish many of the "do's and don'ts" and the planting ideas here are considered by many to be effective, yet other gardeners try them with little success.

Certainly it is worth trying and experimenting to see the impact of mixed planting, especially with so many vegetable gardens moving towards the potager model, and incorporating ornamental plants amongst the cabbages!

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Companion Planting. Attract and encourage good insects
Companion Planting
Attract and encourage good insects

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One of the keys to successful organic gardening, composting is not only easy, it can be fun. Make a compost pile in your garden and reap the benefits.
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Last revised 20 Feb '01