Companion Planting for Pest Control

Companion planting has a long tradition in organic gardening practice. The principle behind companion planting is that certain plants either enhance each other’s growth or help control pests when planted close together. There are also plants that enrich the soil. In addition, companion planting increases bio-diversity in our gardens, by encouraging bees and butterflies.

Companion plants:

There are many elements to companion planting. The starting point is usually the cultivation of plants that enhance or stimulate one another’s growth. The following plants have long been regarded as good companions. 

Plants that enhance or stimulate growth:

  • Chamomile (known as the plant doctor) Lovage, Marjoram, Parsley, Amaranth (morogo), Pennyroyal, oats and legumes (beans/peas) all enhance the growth of nearby plants.
  • Basil is a good companion for tomatoes, cucumber, lettuce and spinach.
  • Borage sweetens strawberries and tomatoes
  • Celery benefits leeks, tomatoes and beans.
  • Plant Dill close to lettuce, mealies, cucumber, carrot and tomatoes.
  • Flax (Linseed) improves the flavour and size of carrots and potatoes.
  • Morning glory (annual) stimulates melon seed, beans and grapes.
  • Nasturtiums improve the flavour of most vegetables.
  • Chervil complements radishes and carrots.
  • Chives are best with carrots, parsley, apples, melon, beans, cucumbers, beetroot, lettuce and gooseberries.
  • Caraway grows best with peas.
  • Mint is an excellent companion to cabbage and peas.

Some bad companions:

  • Don’t plant brassica’s near strawberries, beans or tomatoes
  • Keep carrots apart from potatoes, fennel and cabbages.
  • Fennel is harmful to tomatoes, caraway, beans, dill and coriander.
  • Don’t mix strawberries and garlic or mint and parsley

Plants that condition or enrich the soil:

  • Legumes i.e. peas, beans, Lucerne, Petunias, and Nettle add nitrogen to the soil
  • Amaranth (Morogo), Salad Burnet, Comfrey and Golden Rod are good compost makers, also improve the soil.
  • Mustard is useful to rebuild tired soil
  • Grow celery and dandelions to encourage earthworms.
  • Comfrey is rich in nitrates and phosphorus; add to compost or line trenches with leaves.
  • Flax (Linseed) makes clay soil friable
  • For green manure use oats and mustard.

 Controlling pests and diseases organically:

Controlling pests in the veggie garden is very important if you want a good harvest. Going the organic route is quite complex because you shouldn’t assume that all natural remedies are safe. Some, like tobacco dust, can be toxic. Even when organic formulations claim to be safe to use, it is best to read the labels very carefully.

here are many plants that also assist in repelling insects. Some gardeners rely solely on companion planting for pest control. You need to see what works for you. But it is certainly not a problem to complement your companion planting with organic pesticides or insect repellent sprays.

Companion planting for pest control:

Plants with strongly aromatic leaves generally repel insects and can be interplanted with veggies or flowers. These include Elder, Feverfew, Lavender, Mugwort, Nasturtium, Pyrethrum, Rue, Santolina, Winter Savory, and Garlic.

Other plants release chemicals from their roots that suppress or repel pests and protect neighbouring plants. For example, Marigolds release thiopene, a nematode repellent.

And then there are plants that provide a beneficial habitat for predators like ladybirds, praying mantis and spiders that help keep pest populations in check.

Insect repelling plants for specific pests:

  • Ants – bay, tansy
  • Aphids – catmint, marigolds,
  • Beetles – rose scented geranium
  • Cabbage fly – celery, rose scented geranium,
  • Eelworm/nematodes – marigolds
  • Fruit fly – khakibos, tansy and marigolds
  • Flies – basil, catmint, lemon verbena
  • Fleas – catmint, fennel, Khakibos
  • Mosquitoes – lemon verbena.
  • Snails and cutworms – mustard, oak leaves

Herbs are nature’s most beneficial plants. Not only do they work their magic on food and the body, but they are hard-working garden plants as well. They are an organic gardener’s greatest ally in repelling insects, attracting pollinators, conditioning the soil, aiding composting and enhancing the flavour of some vegetables.

Best insect-repelling herbs:

The strongly aromatic foliage of these herbs deters pests or masks the odour of other plants that are sought after by pests.

Tansy (Tanacetum vulgare) is a very effective insect repellent. It is a perennial, growing 1.2 m high and 1 m wide, with fern-like foliage and clusters of yellow button flowers. It needs good drainage and room to spread.

Pennyroyal (Mentha pulegium) is known for repelling ants and can be planted around wormeries to keep them ant-free. It grows in full sun or shade and the leaves release a strong peppermint fragrance when crushed.

Feverfew (Tanacetum parthenium) is a medium-high (60 cm) annual with strong-smelling and bitter-tasting foliage that repels any insect that comes into contact with it. The white daisy-like flowers attract butterflies and bees. It is a very attractive garden flower.

Chives (Allium schoenoprasum) keep aphids away from roses, grapes, tomatoes, carrots and fruit trees.

Herbs for making natural insecticides:

Fresh or dried leaves or flowers from these herbs can be used in natural insecticides. Steep the herb material in hot water, strain when it has cooled, add a tiny amount of liquid soap for spreading, and spray onto plants affected by pests.

Pyrethrum (Tanacetum cinerariifolium) is a compact, sun-loving perennial (30 cm high and wide) with white daisy flowers in summer. Even the dried flowers can be used as an insect repellent.

The passion fruit daisy (Tagetes spp.) is a medium-sized perennial shrub (1.5 m by 1 m) with golden-yellow flowers, and foliage with a strong passion fruit fragrance that repels white fly on tomatoes, Mexican bean bug on beans and nematodes in the soil.

Wormwood (Artemisia absinthium) and southernwood (Artemisia abrotanum) have pungent grey-green leaves that deter insects. A spray made from the leaves is reputed to repel thrips, snails, slugs, spider mites, and mealybug. Both species produce yellow flowers in summer.

Best herbs for diverting pests:

These are herbs that attract pests to them and away from the veggies. Often referred to as ‘trap crops’, they make it easy to eradicate pests.

Nasturtiums (Tropaeolum majus) and garlic chives (Allium tuberosum) attract black aphids in droves. Pull out the infested nasturtiums and throw them away. Cut garlic chive leaves to ground level and dispose of them. The plants will quickly resprout. Snails love marigolds (Tagetes erecta) and are easily picked off the foliage.

Best herbs for beneficial bugs and bees:

Basil (Ocimum basilicum) in all its forms, both annual and perennial, produces spikes of flowers that attract bees. They particularly like perennial pink basil, which becomes a lovely garden shrub of 60 cm high and 50 cm wide in summer.

Bergamot (Monarda didyma) is a tall annual (80 cm high and wide) that bears beautiful pink-red flowers in summer that attract bees. Grow it in rich soil and water it well.

Lemon balm (Melissa officinalis) is also known as bee balm because the bees love its small white flowers. It has bright-green serrated leaves and dies down in winter.

Coriander (Coriandrum sativum) that is allowed to flower will attract butterflies and bees, while its strong-tasting leaves are loathed by aphids. This annual grows best in autumn and spring.

Yarrow (Achillea millefolium) is a low-growing perennial with feathery leaves and heads of pink flowers. The flowers attract parasitic wasps and hover flies, which are beneficial predators.

Fennel (Foeniculum vulgare), with its large heads of yellow flowers in summer, acts as a trap crop for beetles and aphids but also attracts ladybirds.

Best compost herbs:

Borage’s (Borago officinalis) hairy leaves are rich in minerals, making it a good green manure for adding to compost or making into a liquid ‘green tea’ fertiliser. It is an annual that dies down in winter but re-seeds easily.

Comfrey (Symphytum officinale) leaves are a natural compost activator and can also be infused as a liquid fertiliser. It is a clump-forming perennial that dies down in winter.

Yarrow (Achillea millefolium) has to also be included because its leaves help to break down compost and can also be infused to make a liquid fertiliser.

The information in this article is supplied by Healthy Living Herbs.

The Gardener