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Using Herbs To Manage Garden Pests

The start of a new season is always full of possibilities, and here is a project that may just capture your imagination. How about working with nature to create a natural balance in the garden between pests and their natural predators? It is all about planting a variety of herbs and flowers that act as host plants for the pests, or the beneficial insects that prey on them, as well as using plants that repel pests.

The long-term aim is to have a naturally healthy garden that requires little intervention from the gardener in terms of pest control.

Common pests and their predators

Among the many pests that gardeners have to contend with, the two most common seem to be aphids, which infest both vegetables and flowers, and whitefly, which target a range of veggies. Not only do they suck the sap out of leaf tips, but they also spread plant viruses.

Fortunately, these pests are a food source for ladybirds, lacewings and solitary parasitic wasps. What these three natural predators have in common, besides prey, is that they also feed on the pollen or nectar of the same plants.

Host plants

Common herbs that attract these predators include those with umbrella-shaped flowers, such as anise, dill and fennel, as well as herbs with a profusion of small flowers like yarrow, tansy, scented geraniums, spearmint (allow it to flower), thyme and wild rocket.

Fragrant or nectar-rich flowers are also irresistible, such as alyssum, angelica, coreopsis, cosmos, Queen Anne’s lace, roses, sunflowers and Shasta daisies.

Growing a variety of plants, in groups of at least three of each herb or flower variety, that flower at different times will ensure a constant source of nourishment.

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Dill also attracts hoverflies, which feed on aphids, and will attract tomato hornworms away from tomatoes. It enhances the flavour of cucumbers if planted close to them. Dill thrives in full sun, in fertile, well-drained soil and needs protection from the wind. Don’t plant near fennel.

Other uses: Use the fresh leaves in marinades, salad dressings, to flavour hot and cold dishes (especially trout, salmon, chicken, potatoes and hardboiled eggs) added to sour cream as a dressing for cucumbers, mixed with cottage cheese as a spread and as a garnish for soups and vegetable dishes. Dill tea is drunk as a digestive after a rich meal.

Yarrow has many other garden benefits besides attracting ladybirds, bumblebees, hoverflies, butterflies and wasps. It helps nearby plants resist disease by stimulating their production of essential oils. An infusion of the leaves produces the trace element of copper as a fertiliser for other plants, and its leaves can be used as a compost activator. It grows in full sun and fertile soil that should be kept consistently moist. It produces heads of pink or white flowers in summer.

Other uses: A herbal infusion or tea made from leaves and flowers helps to bring down a fever by promoting sweating, and it should be drunk at the onset of a cold or feverish flu to help recovery.

Host plants for pests

There are other herbs and flowers that act as hosts for the pests themselves, and in that way attract ladybirds and other predators for an easy meal.

Fennel (especially bronze fennel), wormwood (Artemisia absinthium) and wilde als (Artemisia afra), pyrethrum (Chrysanthemum cinerariifolium), roses, petunias, and hibiscus are all magnets for aphids. If the ladybirds and other predators are not cleaning up fast enough, dislodge the aphids with a strong jet of water. Steer clear of organic insecticides containing natural pyrethrins or that are targeted at small to medium beetles, as they will kill these beneficial insects too.

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Bronze fennel is a beautiful foliage plant that is more often found in flower gardens. Like ordinary fennel, it is a perennial that likes well-drained soil and grows in full sun or morning sun. It can grow up to 2m in height. Butterflies, hoverflies and wasps love fennel’s yellow flowers, and these flowers also attract aphids away from other plants. Cut back when the leaves start to fade and the plants will shoot up again.

Other uses: A tea made from the leaves acts as a mild appetite suppressant as well as a diuretic. Both help you to lose weight naturally. The leaves also add a subtle aniseed flavour to fish, poultry and vegetables as well as spicy Indian and Italian dishes.

Insect repelling plants

Herbs with strongly aromatic leaves are effective for deterring pests or for masking the smell of plants that are targeted by pests. These include members of the Artemisia family, tansy (especially for fruit fly), feverfew and catnip (Nepeta cataria), which is disliked by aphids.

Bright and colourful marigolds are also an effective pest repellent, and an essential companion plant in the veggie garden. Their strongly aromatic leaves deter whitefly, various beetles, tomato moths, cabbage white butterflies and moths, and can also be used to make insect-repelling sprays

In addition, they keep eel worms away by secreting a chemical substance through their roots. It has recently been found that the roots also encourage the growth of mycorrhizal fungi, which exchange nutrients with host plants for their mutual health and growth.

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Wormwood and wilde als are both striking foliage plants with strongly aromatic silvery-grey leaves and tiny creamy-yellow flowers. The bitter leaves can be used to make an insecticide against caterpillars, whitefly and aphids that won’t harm bees and other beneficial insects. Wormwood is known to inhibit the growth of nearby plants but will be effective if grown in nearby containers.

Other uses: Make this wormwood repellent spray: Simmer 250g of wormwood/wilde als leaves in 2 litres of water for 30 minutes. Strain and cool. Dilute 5ml dishwashing liquid in 500ml hot water. Mix the two and spray aphid-affected plants.

Tansy is a frost-tolerant perennial that grows 1.2m high and 1m wide, with fern-like foliage and clusters of yellow button flowers that add interest to the garden. It is particularly effective in repelling fruit flies and should be planted underneath or around fruit trees. The flowers attract lady birds and other natural predators. Plant it in full sun, in composted soil that drains well.

Feverfew is a dense, perennial flowering plant with white daisy flowers that attract butterflies and bees, while its strong-smelling leaves effectively repel insects. It grows best in full sun. Being attractive to bees, it is often planted near fruit trees to assist in pollination.

Other uses: A tea made from the leaves may relieve migraines and indigestion.

Insect trap plants

Another type of plant to include in your arsenal of pest-controlling plants is the ‘trap’ plant. This also acts as a host plant to the pests, and once infested with pests is pulled out or cut down to ground level. The infested plant material is destroyed or thrown in the dustbin, not on the compost heap!

Nasturtiums are a well-known plant for attracting aphids or squash bugs. They draw the pests away from veggies like tomatoes, beans and squashes. The flowers attract pollinators as well as hoverflies, which also prey on aphids.

Chives and garlic chives are also a magnet for aphids, and a common practice is to plant them thickly as a border for roses. Cut down the infected plants to ground level and throw the leaves away. Being bulbs, chives are quick to re-sprout.