The Best Pest Treatments for UK Houseplants

Pests are the category you don’t think about until you suddenly need it. Before reaching for a spray, it’s worth knowing that most infestations can be prevented, and many early ones can be dealt with by hand.

It’s also worth knowing the law. In the UK, a product used to control pests on plants has to be authorised as a plant protection product. Neem oil — widely recommended online — is not authorised as a pesticide in the UK, and Which? advises that it shouldn’t be on sale for that use. We no longer recommend it. If you buy a spray, check that its label says it’s authorised for use on indoor or ornamental plants, and follow the label.

What follows is four approaches, ranked by when to use them. They’re research-led: drawn from RHS guidance and manufacturers’ published information rather than our own treatment trials.

Start Here — New-Plant Quarantine

The cheapest pest tool of all, and the one that prevents most infestations from ever starting. Most pest problems in a houseplant collection arrive on a new plant — garden centres, online sellers, and even reputable specialists can’t guarantee a pest-free plant, because eggs and soil-stage larvae are hard to see at the point of sale.

The protocol is straightforward: every new plant gets a two- to three-week quarantine in a room away from your existing collection. Check the undersides of leaves weekly, ideally with a magnifying glass, and watch the compost surface for small flies. If a plant comes through clean, it joins the collection. If it doesn’t, you’ve caught the problem before it spread.

It costs nothing except a little space and the patience to delay introducing a new plant for a fortnight or so.

Best Spot Treatment — Hands-On Removal

The first response to most early infestations is physical, and it’s often enough.

• Mealybugs and scale insects have a waxy or shell-like coating that protects them. Wipe them off with a damp cotton bud or a soft brush, paying attention to leaf joints and stem bases where they cluster.
• Aphids are soft-bodied and exposed. Rinse them off with a stream of water, or wipe them away by hand.
• Spider mites thrive in dry air. Rinse the plant thoroughly — especially the leaf undersides — in the shower, and raise the humidity around it.
• Heavily infested leaves are best removed altogether, which takes a large share of the population with them.

Hands-on removal works for visible, early infestations. Because eggs and hidden insects survive, check again every few days for several weeks and repeat as needed. For a widespread infestation, isolate the plant and consider an authorised treatment.

Best for Fungus Gnats — Dragonfli Fungus Fly Killer Nematodes

Fungus gnats (sciarid flies) breed in damp compost. The RHS notes that their larvae feed mainly on dead roots and decaying plant material, and that established plants are unlikely to be damaged — so they’re more of a nuisance than a threat for most collections. The first fix is cultural: let the compost dry out more between waterings, since gnats are more numerous in constantly wet compost.

For a stubborn population, the RHS lists Steinernema feltiae — a pathogenic nematode you water into the compost — among the biological controls available by mail order. Dragonfli’s Fungus Fly Killer is one such product: mix the nematodes with lukewarm water and water them into the compost so they reach the root zone. The smallest pack (5 million nematodes, around £9.99) treats up to 25 houseplants. The nematodes need compost above 10°C, the pack should be kept in the fridge and used promptly, and Dragonfli recommends repeating after four weeks.

Pair with yellow sticky traps to catch the adult flies while the nematodes work on the larvae.

Best Monitoring Tool — Yellow Sticky Traps

Yellow sticky traps are not a treatment — they’re a monitoring tool that catches the adult stage of flying pests such as fungus gnats. The colour attracts the insects; the sticky surface catches them. They tell you what’s flying around your collection and whether your treatment is working: if a trap stops catching anything for a couple of weeks, the problem has probably cleared.

They won’t end an infestation on their own, because most adults have already laid eggs by the time they fly into a trap. The RHS also notes that they can catch large numbers of non-target insects, including predators — so use them where you need them rather than everywhere, all the time.

What to skip

Neem oil as a pesticide. Not authorised as a pesticide in the UK. See above.

Homemade sprays. Garlic, chilli, soap, and similar home-made pest sprays aren’t authorised plant protection products either, and their effect is unreliable. Physical removal does the same job more dependably for early infestations.

Ultrasonic pest repellers. Plug-in devices that claim to drive insects away with high-frequency sound. We haven’t found good evidence that they work on houseplant pests.

How we chose

These approaches are research-led. They’re based on RHS guidance and on manufacturers’ published information, and we’ve checked UK prices and the UK legal position in October 2026. We haven’t run our own treatment trials, and we don’t claim to have. See how we review.

For pest identification — which pest you actually have before you reach for treatment — see the pest field guide hub.

Sources

• RHS: Fungus gnats (sciarid flies) — larval feeding, cultural control, yellow sticky traps and their non-target catch, biological controls including Steinernema feltiae.
• Dragonfli: Fungus Fly Killer Nematodes — organism, pack sizes and coverage, price, application, temperature, storage, repeat treatment.
• Which?: 5 things to not do in your garden (June 2026) — neem oil not authorised as a pesticide in the UK; HSE guidance on legal garden chemicals.
• Greenhouse Stores: Homemade pesticides and the law — plant protection product rules and home-made sprays.

Correction, October 2026: an earlier version of this page recommended a neem oil product we can’t find on sale and neem as a pesticide, which isn’t authorised in the UK; it also recommended a US fungus-gnat product and described treatment trials we had not carried out. It has been rewritten from RHS guidance and manufacturers’ published information. See how we review.