How to keep your garden free from aphids

ARTICLE Anja Kussler 

Aphids, also known as plant lice, are one of the most destructive insect pests to attack cultivated plants grown in temperate regions. Think most of New Zealand! 

Of the 4,000 species of these sap-sucking green, yellow, brown, red or black insects that exist worldwide, 250 are harmful to crops and heavy aphid infestations can cause large-scale damage to your garden. The tiny insects achieve this by piercing the stems of plants (especially new growth) and then suck out the nutrient-dense sap the plants need to thrive. Plant lice often also transmit viruses to host plants during feeding, and these can be especially lethal to crops like potatoes, citrus fruit and grains. 

What’s more, the sweet, gooey honeydew liquid the aphids secrete as they munch along creates the perfect environment for mould to grow and spread, depriving the plant of essential sunlight.

Whilst they’re not usually harmful in low to moderate numbers, these 1 to 10mm long, pear-shaped critters multiply fast – most of the species don’t need to mate in order to procreate, so they produce live offspring rather than having to wait for eggs to hatch… 

As you can see, if you want your garden and veggie patch to flourish, it’s paramount to keep plant lice well at bay. Fortunately there are several ways of controlling them organically and safely, without resorting to toxic chemicals. 

By hand 

For smaller infestations, grab a pair of gloves and brush the aphids from the stems and leaves of the plant. If only a couple of branches are affected, prune them off and immerse them in soap water to kill the pests. 

Hose them

You can use a garden hose to spray smaller aphid populations off more robust, mature plants, but beware that this method may ‘injure’ younger, more fragile host plants.

Good old soap and water

A few tablespoons of eco-friendly dishwashing liquid diluted in 1 litre of lukewarm water and sponged or sprayed onto the plant can help control low to moderate aphid infestations. The soap will dissolve the aphids’ waxy protective coating, dehydrating and killing them without harm done to the plant. Please note: soap also kills beneficial insects like ladybugs (see step 5) so use this method sparingly.

Grow aphid-repelling plants 

Planting certain flowers, trees, shrubs and herbs in your garden can effectively help control plant lice by attracting natural aphid predators. ‘Anti-aphid’ flowers include dahlias, asters, orange-petalled nasturtium, marigolds, alliums, sunflowers and petunias. Petunias are especially popular as they’re easy to grow, look gorgeous and will keep beans, tomatoes and basil lice free when grown alongside them. (Tip: look for wildflower seed packs containing special ‘insect blends’).

Herbs and flavour givers that can help keep your garden free from aphids include dill, eucalyptus, fennel, lavender, calendula, basil, onion and garlic. Garlic works particularly well in keeping roses aphid free, which is why planting them in a bed of these delicate thorny blooms is a great idea.  

Work the DENZ magic

Diatomaceous Earth is a fully non-toxic natural pesticide made up of tiny fossilised organisms found at the bottom of the ocean. It kills plant lice – and other bugs – by scoring their outer layer as they crawl over the fine powder, giving your plants long-lasting protection in the process. What’s more, DENZ kills parasites in the human body and can be used as a natural de-wormer for pets, too.

Essential oils

A concoction of 4 drops each of thyme, peppermint, clove, and rosemary oils mixed into a spray bottle filled with water will kill plant lice, including their eggs and larvae. Neem oil diluted in water (used sparingly) may also deter aphids.

Anti-bug birds

Encourage the nesting of aphid-eating birds such as wrens, chickadees and titmice in your garden. Do this by offering them ‘free accommodation’ on your property in the form of small shrubs and bushes like hydrangeas, abelia or other dense plants that provide cover against predators, as well as evergreen bushes and trees like boxwood and privet. And once the ‘accommodation’ is sorted, we’re sure they’ll fancy the free food (aphids) that comes with the deal!

Shoo away the ants

Ants fancy feasting on the honeydew aphids secrete whilst feeding so they’ll often protect aphid colonies. Draw the ants away from the aphids with small containers of honey placed near the base of the infested plant – with the ants out of the way birds and predator insects will gain better access to the aphids.

You might be interested in Companion Planting if you are planning your garden.  

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*All information is believed to be true at time of publishing and is subject to change.