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Companion Planting

It is not normal for any living thing to grow up in isolation, or in contact with only others of its same kind. Diversity and interconnection are basic ecological principles. Companion planting is the gardeners way of creating diversity in the garden.

Companion planting helps in all kinds of ways to reduce pest numbers and creating favourable growing conditions. You can follow books and charts - which may or may not be appropriate to your location. You can also think about the following ways that companion planting works and experiment for yourself.

Scent  
Strongly scented herbs will mask the scent of other plants, confusing pests, which identify their targets by smell. Example: Brassicas when planted among sage, rosemary or dill, will suffer less damage from the caterpillars of the cabbage white butterfly.

Attracting Predators
Providing food and habitat for predators and parasites will reduce the numbers of pests in a garden. Example: Parsnip flowers provide a food supply for parasitic wasps.

Repelling or killing pests
Some plants are toxic to pests. Example: French Marigolds will kill off some harmful nematode species.

Altering appearance
Flying pests often identify their food supply by its shape. Growing different plants closely together ensures that there are no distinctive outlines for pests to identify.

Shelter
A carefully placed stand of taller plants creates a sheltered spot. Example: Plant corn near pumpkins.

Support
The stalks and branches of a large sturdy plant can support a climber. Example: Sweet peas climbing through the low lying branches of an orange tree.

Nitrogen fixing
Leguminous plants host bacteria in their roots. These bacteria fix nitrogen, supplying this nutrient to their hosts and indirectly, to neighbouring plants. Example: Clover grown around cauliflower.

Some plants don't want too much nitrogen so keep them away from legumes. Example Don't put onions near peas. They will grow well but store poorly.

Allelopathy
Substances released from plants into the soil can affect the growth of neighbouring plants. Many plants inhibit the growth of others, but a few enhance it. Example: Plants promoting the growth of others nearby include nettle, calendula, yarrow and (planted sparingly) chamomile.

Minerals
Deep rooted plants draw up minerals from the subsoil, returning these nutrients to the topsoil. Example: Comfrey draws up potassium, which is released into the soil as the leaves die off in late autumn.

Bad Companions
Plants to avoid in or near the garden include large trees, (particularly conifers, eucalypts and walnuts), strongly bitter herbs (wormwood, southernwood, tansy, rue) and heavy feeders which may also release growth inhibitors (brassicas, sweet corn, sunflowers).

Intercropping
Save space by growing small, quickly growing vegetables between larger slower growing ones. The small vegetables can be harvested before the larger ones claim their growing space. Example: Plant lettuces between tomatoes.

Guilds
A small number of plants which all grow well together is called a guild. A common three plant combination is sweet corn, pumpkin and climbing bean. A common four plant combination is tomato, basil, marigold, and lettuce.

Other factors to consider when deciding what to plant with what include: size, growth rate, root depth and type, nutritional needs, soil conditions, soil type and watering needs.