Yellow sticky traps for fungus gnats on houseplants
Updated: 17 October 2026
You water a houseplant and small dark flies lift off the compost, then settle when the surface is still. Yellow sticky traps for fungus gnats catch the adults that land on the glue and leave the larvae in the damp mix, so a full card can stand in a pot that is still producing flies. Pack size and mounts are on the [yellow sticky traps comparison](/hub/traps/yellow-sticky-traps). This page uses UK guidance and amazon.co.uk review comments, not a lab test. A qualifying purchase can earn a commission at no extra cost to you.
You water a houseplant and small dark flies lift off the compost, then settle when the surface is still.
You water a houseplant and small dark flies lift off the compost, then settle when the surface is still. Yellow sticky traps for fungus gnats catch the adults that land on the glue and leave the larvae in the damp mix, so a full card can stand in a pot that is still producing flies. Pack size and mounts are on the yellow sticky traps comparison. This page uses UK guidance and amazon.co.uk review comments, not a lab test. A qualifying purchase can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Placement | Indoor only | Pack size | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  MSR Traps MSR Traps 35 pack | Angled in soil | Yes | 35 | 7.7 | about £4.99 | View offer |
| Best value |  aonova aonova 60 yellow cards | Soil or flat | No | 60 | 8.7 | about £5.99 | View offer |
 Blooven Blooven 60 yellow cards | Into soil | Yes | 60 | 9.2 | about £6.99 | View offer |
On this page
Flies off the compost are usually fungus gnats
Those flies are fungus gnats, the sciarids the Royal Horticultural Society links to damp compost. Larvae feed on decaying matter and can nick soft growth on a seedling, while a mature plant often shows little damage. Gardeners' World says you may mistake them for fruit flies, though flies that leave the pot are likely sciarids.
Fruit flies belong with a caddy or fruit on the side. If the swarm is over the bananas and the pots are quiet, use yellow sticky traps for fruit flies, where a yellow card is a weak match for a kitchen source. Tap the pot. Flies from the compost mean that pot is the breeding site, and the card only meets adults that have already left it.
The card catches adults that land on it
The trap works when an adult lands on the glue. The Royal Horticultural Society says cards near the plants can reduce adult numbers, and that they can also catch predators. Gardeners' World keeps the card near soil level.
Press a pointed card in so the sticky face starts just above the compost. If you bury the glue or leave the film on, the card does nothing useful. Peeling and replacing are on how to use yellow sticky traps.
Blooven, aonova and MSR reviewers on amazon.co.uk say adults stick, and that wet compost or no larval treatment leaves the gnats. One MSR reviewer said a larval treatment still took about three weeks. A crowded card shows adults are flying. It does not show the pot is clear. In a protected crop, AHDB says monitoring traps catch sciarid adults and are not enough to bring numbers down.
Larvae stay in damp compost
Gardeners' World places the larvae in the top 5–8 cm. Let that layer dry between waterings, although a fern that collapses in a dry root ball needs a shorter gap than a plant that tolerates drought. Empty a full saucer, or the surface never dries. A grit mulch, which Which? and Gardeners' World mention with the traps, makes the top less inviting and leaves larvae under the stones. Change only the card, on the same wet routine, and the next adults stay in the pot.
For a larger collection, those sources name Steinernema feltiae as a nematode drench. Which? uses it above 10°C in the compost. AHDB's herb guidance recommends the same species at about 10–30°C, depending on the product, so follow the pack rather than a blended range. Gardeners' World keeps the drench indoors, and this page sets no dose. Dry the surface first, and drench only if adults keep emerging after that, while the compost is warm enough.
Keep the card indoors. Outdoor sticky traps catch butterflies, hoverflies and predators. That is the warning from the Royal Horticultural Society and Gardeners' World, and the word garden on a listing does not remove it. Under glass, a yellow sheet monitors glasshouse whitefly rather than controlling it, and it can catch Encarsia.
Do not call the card a pesticide
Amazon.co.uk lines often say the card gets rid of gnats, or that the glue is non-toxic. Read both as seller copy. Health and Safety Executive guidance says kill, control, eliminate and prevent are not the wording for a monitoring-only trap. A card with colour and glue, and no pheromone or other active substance, may fall outside the Biocidal Products Regulation, which the seller must justify if challenged, and a trap sold only to monitor needs no biocidal authorisation. Marketed to reduce, control or mass-trap, it can come under GB rules in England, Scotland and Wales, or EU rules in Northern Ireland, and that is not an approved pesticide.
Non-toxic is not a UK safety test. The glue sticks to skin and pet fur, so a cat that rubs the card can carry adhesive off in its coat. A pack that is not as described still falls under the Consumer Rights Act 2015, separate from larvae left in wet compost. Count and mount are on the yellow sticky traps buying guide. The card records adults you can see, and the next generation stays in the compost until the surface dries or you treat the larvae.
Common questions
Will a yellow card kill fungus gnat larvae?
A yellow card does not kill fungus gnat larvae in the compost. The glue catches adults that land on it, and Gardeners' World puts the larvae in the top 5–8 cm. The Royal Horticultural Society treats the cards as a way to reduce and monitor flying adults, not as a cure on their own. If the compost stays wet, new adults keep leaving after the card fills. Drying the surface, or a warm-compost nematode drench, has to sit beside the trap.
Where should the card sit for fungus gnats?
Put the card near soil level, as Gardeners' World does for houseplant flies. Press a pointed card in so the sticky face starts just above the compost. Hung high, it misses flies that stay at the rim. Peel the cover off, and do not bury the glue, or the trap fails and the mix gets a smear. Keep the card indoors, and replace it when the face is crowded or the glue has dulled.
Why are the flies still there after the card is full?
A full card means adults have landed, not that the larvae have left. Blooven, aonova and MSR reviewers on amazon.co.uk say the flies stick, and that wet compost or no larval treatment leaves gnats. One MSR reviewer said that treatment still took about three weeks. AHDB says monitoring traps catch sciarid adults and, in a crop, do not by themselves reduce the population.
Does letting the compost dry help?
Drying the surface between waterings removes the damp film larvae use in the top of the pot. A fern that wilts in a dry root ball needs a shorter gap than a tougher plant. Empty the saucer, or the compost stays wet from below. Grit on top is less welcoming, though larvae already underneath remain. The card shows whether adults are still emerging. It does not dry the pot.
What is Steinernema feltiae for, and when is it too cold?
Steinernema feltiae is a nematode drenched onto larvae in the compost, not a coating for the yellow card. Which? points to it when the compost is above 10°C. AHDB's herb guidance recommends the same species at about 10–30°C, depending on the product. Below the figure on your pack, wait, and keep a drier surface plus a soil-level card. Gardeners' World keeps this drench indoors. Take the amount from the label.
Are fungus gnats the same as fruit flies?
They are different insects. Fungus gnats rise off damp compost. Fruit flies gather on fermenting food, a caddy or ripe fruit. Gardeners' World says the mix-up is easy, and that flies in the pot are likely sciarids. A yellow card is a fair monitor beside the compost and a weak one for a kitchen source. If the flies stay with the fruit, clear that source rather than adding another card to the pot.
Related pages
Sources
Public UK sources for fungus gnats, whitefly, thrips monitoring, and what a monitoring trap may claim. Listings are the amazon.co.uk captures for these eleven ASINs, not a live reload on 17 October 2026. Prices on amazon.co.uk move.
- RHS, fungus gnats (retrieved 17 October 2026)
- RHS, glasshouse whitefly (retrieved 17 October 2026)
- RHS, indoor sap-feeding insects (retrieved 17 October 2026)
- HSE, insect monitoring traps (retrieved 17 October 2026)
- AHDB, thrips monitoring (retrieved 17 October 2026)
- Gardeners' World, house plant flies (retrieved 17 October 2026)
- Which?, fungus gnats (retrieved 17 October 2026)
- Citizens Advice, faulty goods (retrieved 17 October 2026)