Houseplant hacks: does washing-up liquid get rid of pests?

The problem
Few things test a plant-lover’s patience like a pest infestation. The internet is full of DIY advice, and one of the most popular tips is to mix washing-up liquid with water and use it as a pest spray. It’s cheap, easy and always within reach. But it’s not without risk.

The hack
A diluted detergent solution is said to break down the waxy coating of soft-bodied pests, dehydrating them on contact. It can work wonders on aphids, spider mites and thrips, killing them quickly without the need for harsh chemicals. But household detergents weren’t made for plants. The wrong formula or a heavy hand can cause serious leaf burn, leaving behind residue that stresses your plant more than the pests did.

The method
Mix half a teaspoon of mild, fragrance-free washing-up liquid into 1.5 litres of water. Shake gently, then test on one or two leaves first. Leave for 24 hours to check for damage. If the plant tolerates it, lightly mist affected areas, but never drench the whole plant. Rinse thoroughly with clean water after 10–15 minutes. Always spray on a dull day or in the evening ; combined with strong sunlight, soap can scorch leaves.

The test
The solution didn’t shift mealybugs on my jade plant, but worked brilliantly on a nearby coleus plagued by aphids; they were gone within days, with no damage.

The verdict
Washing-up liquid works as a gentle deterrent for soft-bodied pests but won’t conquer tough infestations like mealybugs. Use sparingly, test first and always apply when sunlight is low to avoid scorch marks.