Ivydene Gardens Garden Design:
Companion Planting
 

1. Plants may help each other directly:

providing shelter from wind, such as hedges.

providing shelter from sun, such as leafy groundcover under clematis keeps their roots cool.

root secretions — root exudates from peas help other plants to absorb nutrients ‘independently’ of the nitrogen-fixing ability that peas and other legumes have.

root channels — during a plant’s life the root hairs are continually replaced and once it is dead, the larger roots start to decay as well, so providing nutrients from the breakdown. This is why rotation and interplanting are important — a different type of plant will be better able to use these ‘second hand’ nutrients and runs less risk of disease than if the same species is planted again in the same place.

 

2. Plants may help each other indirectly by improving the soil

mineral accumulators — plants use leaves they are about to shed as dumping grounds for unwanted minerals and by-products, which will then feed the microlife and thus the future crops. The following minerals are essential to the health of many plants — although some may be needed in only minute amounts (so known as trace elements):

Element

Purpose

Supplied by Plant

Boron

for apples and brassicas

Euphorbia

Calcium

binds plant cells together

Beech and Broom

Copper

leaf growth

Yarrow

Cobalt

leaf growth

Vetch

Iron

leaf growth

Beans and Foxgloves

Magnesium

leaf and root growth

Oaks and Potatoes

Manganese

beet growth

Comfrey

Nitrogen

vegetative growth

Any legume

Phosphorus

root growth

Oak leaf

Potassium

fruiting and disease resistance

Apple leaves and Sunflowers

Silica

toughens plants, disease resistance

Onions and Stinging Nettles

Sulphur

disease resistance

Brassicas and Horseradish

I use Calcified Seaweed as a top dressing to provide trace elements during soil conditioning.

green manures — flax and Phacelia improve the tilth and bind together soil particles. These are then dug in and left to rot for a fortnight before replanting.

humus and texture improvers — spinach adds saponins which gel the humus with coarser organic materials, helping it to hold more water.

 

3. Plants may compete with and/or directly harm others:—

competition as such — Tagetes minuta (Mexican Marigold) is a smother crop to suppress bindweed and equisetum. Its root secretions also kill nematodes (minute parasitic worms which attack tomatoes).

root and leaf secretions — clovers are inhibited by root secretions from buttercups and disappear when buttercups appear.

replant disease — allelopathic compounds will prevent a replacement plant from establishing itself for several years until they have broken down. This is worst for woody plants especially roses, apples and black walnuts.

 

4. Some plants help others if they are present in a small proportion, but hinder or harm them as the ratio increases

stinging nettles make fruit, particularly tomatoes, ripen fully with less rotting.

 

5. Plants may repel harmful insects or attract them away from other plants

camouflage: a plant with a stronger odour may ‘hide’ another, or use leaf patterns or the ‘wrong’ flowers to camouflage it. For example, growing carrots and onions together can confuse their respective pest flies.

sacrificial planting: the companion is sacrificed for the benefit of the valuable crop. Wild blackberries in the hedges will reduce damage to other fruits in the autumn.

tree plants: nasturtiums can be grown up through apple trees to drive away woolly aphis.

 

6. Plants may support insect populations which are beneficial to other plants

7. Plants may repel other and larger pests

thorny or prickly plants discourage cats and dogs from fouling the soil. Some plants give off smells that are repulsive to animals:—
Dwarf Elder discourages mice
Onions discourage rabbits
Wormwood discourages slugs and snails.

 

8. Plants may attract birds and other creatures which prey on pests and/or are generally beneficial

birds can be encouraged with plants offering perches, shelter and food from fruits and berries. Dense plant shelter attracts hedgehogs, frogs, toads, newts and slow-worms, which eat pests.

 

9. Plants may reduce the incidence of fungal or other diseases in nearby plants

when a green manureof flax or mustard breaks down in the soil, it releases cyanide gas and related compounds in minute amounts; this kills fusarium, elminthosporum and verticillium.

 

10. And, finally, plants may be attractive and/or beneficial to animals and people.

The Companion Planting Section contains further information.