Aphids, also known as greenfly or blackfly, are tiny, sap-sucking bugs that can occur on most plants, particularly on soft young growth. There are actually more than 500 species of aphid in the U.K., varying in colour from green and black to also yellow, brown, and orange, and in size from 1mm to 7mm long.


Aphids need warmth to flourish, so in the garden this limits their lifecycle to spring and summer. However, indoors in the home, greenhouse or conservatory, aphids can occur at any time of year. Many types of aphid feed only on specific plants, so an infestation on one plant doesn’t necessarily mean that it will affect all of your plants.

More on tackling aphids:

How to get rid of aphids on house plants

Why are aphids a problem?

Greenfly on a leaf
Greenfly on a leaf

Greenfly and blackfly are a natural part of the garden ecosystem and a vital source of food for many species of bird, including house sparrows. They're only a problem if they occur in large numbers. Large infestations can weaken plants and cause curling or distortion of affected growth. This can sometimes eventually kill the plant, especially young ones. Some aphid species transfer virus diseases between plants – there are many viruses that cause a range of symptoms including mottled, streaked or distorted foliage, and weak growth. Viruses aren’t curable so infected plants should be destroyed. An additional problem caused by greenfly and blackfly is the sticky substance they exude, known as honeydew, which can become infested with black mould – this stops leaves photosynthesising and inhibits plant growth.

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What should I do if I spot aphids?

A small number of aphids on a garden plant is rarely a problem. Birds will quickly pick them off and feed them to their young. However, in the veg patch, where you might be growing lots of the same plant together, or indoors where there are no natural predators, so you'll need to act quickly. Often simply hand-squashing a small infestation is all that’s needed. Be alert for early warning signs and inspect plants thoroughly – greenfly and blackfly can be hard to spot as they nestle in leaf joints and on the undersides of leaves, and often the first warning sign on indoor and greenhouse plants is the sticky honeydew on the leaves beneath the initial cluster. Ants running up and down plant stems is another giveaway sign of greenfly in the greenhouse, as they ‘farm’ aphids and feed on their sweet honeydew.

Encouraging wildlife to control aphids

How to control aphids (greenfly or blackfly)
Ladybird and greenfly

Many wild species eat greenfly and blackfly and actually rely on them as an important food source. Aphid predators include birds, ladybirds, hoverflies, lacewings and earwigs. Ladybirds, hoverflies and lacewings lay eggs on plants infested with greenfly and blackfly and their young eat them at an astonishing rate – it's thought that one ladybird can consume several hundred aphids over its lifetime. Wasps are voracious feeders of aphids, too, so instead of regarding wasps as villains, leave them alone to help control pests. In spring, aphid populations may rise to begin with as predator populations can be low, but later in the season these predator populations will be rising to get aphids under control.

Controlling aphids without chemicals

Spraying aphids off with water
Spraying aphids off with water

The chances are that, by the time you've found greenfly or blackfly on your garden plants, the predators have, too. So bear in mind that removing aphids will likely kill beneficial insects such as ladybirds and lacewings, as well as aphids. These predators are not present indoors so you will need to control aphids yourself:

  • Wash off greenfly with a jet of water from a hose
  • Hand-squash small infestations
  • Use biological controls, which involve buying live predators into the home or greenhouse to deal with aphid infestations

Learn environmentally friendly methods for controlling greenfly and blackfly, and other garden pests with Monty's guide to organic insecticides and how they work. Monty also talks you through how to make your own, organic pesticide:

How to deter aphids naturally

  • Pungent-smelling plants like sage, onions, garlic, and nasturtium, grown alongside susceptible plants may help deter aphids.
  • Create habitats to encourage birds and other predators into your garden – be less tidy in winter so ladybirds can hibernate, encourage birds with climbing plants and dense shrubs
  • Aphids target soft young growth so minimising use of nitrogen-rich fertilizer helps raise tough-leaved plants (nitrogen is the major nutrient used to develop leafy growth)
  • Thoroughly clean out greenhouses and conservatories once or twice a year. Remove all plants and debris such as fallen leaves; wash surfaces and staging; avoid storing pots and sundries with your plants (they provide hiding places for pests), and fumigate the structure using a chemical-free product

Using sprays to combat aphids

There’s a wide range of chemical-free (organic) products, those based on synthetic products, and chemicals (insecticides).

  • Organic (chemical free) sprays are based on plant extracts, plant oils or soft soap. These must be sprayed directly on the aphids in order to work and often only persist for a short time, so may need re-application
  • Products based on surfactants or fatty acids have fewer harmful effects than chemical pesticides
  • Chemical sprays are based on synthetic pyrethroids. Avoid using sprays containing neonicotinoids due to their harmful effects on bees
  • Always follow instructions and do not spray plants in flower as beneficial insects, bees and others are likely to be killed. Apply sprays late in the day when insects are less active

Frequently asked questions

Is there a home-made, organic way to deal with aphids?

There are many home-made recipes for killing aphids – the most common is using dishwasher liquid mixed with water and sprayed on to the plants. Bear in mind that, because these are home-made, they are not tested for their effectiveness on aphids or of any side effects on the plants. To minimise any adverse effects on the environment, use only eco detergents, and use a very weak solution. Also consider not removing the aphids at all – they are a vital source of food for many other species, including house sparrows and ladybirds, which which control them naturally for you.

If I spray insecticide on aphids will it get into the compost and kill the plants?

Chemical insecticides are designed to kill insects, so spraying them on your plants will kill aphids but may also kill ladybirds, hoverflies and even bees and butterflies, if the insecticide gets into the flowers. Residues will be washed off the plants into the soil and could then harm soil invertebrates such as earthworms and beetles. The insecticide itself won't kill your plants but it will damage the environment of your garden, which will disrupt the ecosystem and make it harder to control pests in future. We recommend letting nature take its course: let birds, ladybirds and hoverflies control aphids unless there is a huge infestation and then remove them by hand or with an organic spray. There should be no need to ever use chemical insecticides in the garden.