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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.
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.
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.
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.
A carefully placed stand of taller plants creates a sheltered spot.
Example: Plant corn near pumpkins.
The stalks and branches of a large sturdy plant can support a climber.
Example: Sweet peas climbing through the low lying branches of an
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
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.
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.
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).
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
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.