Brilliant florist's tip: How matches can drive fungus gnats out of flower pots.

As autumn and winter set in, houseplants often get moved closer to windows - and, all too often, watered a little too generously. That is when they tend to appear in droves: tiny black flies hovering and “dancing” above the compost. In many nurseries and flower shops, professionals reach for an unassuming aid that sounds more like a barbecue accessory than plant care: the matchstick. Behind this seemingly odd trick is a surprisingly effective way to tackle fungus gnats.

What’s actually flying around: fungus gnats, not fruit flies

If you think of summer fruit bowls, fruit flies may be the first thing that comes to mind. In many plant pots, though, the culprit is something else entirely: fungus gnats. They tend to sit on the compost surface or flutter just above it.

The adult insects are mostly a nuisance, but the real problem is their larvae. The larvae live in the upper, damp layer of compost, feeding on organic matter - and they can damage fine houseplant roots. Over time, that can leave plants noticeably weakened.

"Fungus gnats thrive in consistently damp, compact compost - wet potting compost is their nursery."

Common signs of an infestation include:

• When you move the pot or tap it, small black gnats rise up from the compost.
• The compost surface looks permanently damp, cool, and slightly tacky.
• The plant grows more slowly, leaves turn yellow, or the plant looks “tired”.

Why florists push matchsticks into the compost to tackle fungus gnats

In some florists and nurseries you’ll spot a line of small sticks tucked around the rim of pots - ordinary matchsticks. They are inserted into the growing medium with the match head facing down. From the outside it can look like a quirky habit, but there is a chemical reason for it.

Many match heads contain, among other substances:

• sulphur
• potassium chlorate
• red phosphorus
• in some cases additional compounds such as ammonium phosphate

When you water the plant, tiny amounts of these substances dissolve in the immediate area around the match head. Sulphur in particular can slightly shift the pH and the microflora in the top layer of compost.

"The match head makes the conditions at the compost surface unpleasant for fungus gnat larvae - the population collapses."

With fewer suitable micro-organisms available as food, larvae are disrupted and the reproduction cycle is interrupted. For many florists, that is enough to reduce an infestation significantly without immediately resorting to insect sprays.

How to use the matchstick method correctly at home (fungus gnats)

Anyone who wants to copy this professional approach in the living room should do it methodically. It takes a bit of patience, but it avoids using a spray-based poison.

Step 1: Confirm you’re dealing with fungus gnats

Before you start, a quick check is worthwhile:

• Gently shake the pot or nudge the plant - if small dark gnats fly up from the compost, it strongly suggests fungus gnats.
• Press a finger into the top layer - if it feels constantly very wet and cold, that points to overwatering.
• Keep your attention on the compost, not fruit bowls or bins - fruit flies are more typical in the kitchen, whereas fungus gnats stick close to pots.

Step 2: How many matchsticks, and where to place them

For a typical pot around 15 centimetres in diameter, the following amount is commonly used:

• Insert 3 to 5 matchsticks with the heads pointing down into the compost
• Push them in to a depth of about 1 centimetre
• Space them in a ring around the pot edge, not right next to the plant stem

Beforehand, you can lightly loosen the top layer with a fork. This helps the surface dry out and further worsens conditions for the larvae.

Step 3: Application schedule

Two main approaches circulate in nurseries, and both can be used at home:

• Intensive option (as florists do it): Replace the matchsticks every 3 days, over a period of about 15 days.
• A slightly more convenient everyday option: Bury 8 to 10 matchsticks halfway around the pot rim, replace once a week, for 3 weeks.

At the same time, allow the compost surface to dry slightly between waterings, and always pour away excess water from saucers.

Without proper watering, even the best trick won’t work

If you continue watering too heavily, matchsticks alone will not deliver lasting results. Fungus gnats actively seek out wet, humus-rich compost to lay their eggs. When compost stays constantly soaked, they still find good conditions even with matchsticks in place.

"The combination of adjusted watering and matchsticks works - one without the other is rarely enough."

Key questions to keep moisture under control:

• Does the pot have a drainage hole in the base?
• Is there a drainage layer of expanded clay or gravel at the bottom?
• After watering, is the saucer allowed to sit completely full of water?

If any of these are effectively a “yes” in the sense of waterlogging, start there: water less, tip out water from the saucer after a few minutes, and replace old compacted compost when you can.

What else helps against fungus gnats

Many hobby gardeners pair the matchstick trick with other straightforward measures to get rid of these tiny pests. For example:

• Yellow sticky traps: Adhesive yellow cards catch adult gnats before they can lay new eggs.
• A thin sand layer: A 1 centimetre layer of fine sand on top makes it harder for larvae to reach the surface.
• Dry coffee grounds: Sprinkled sparingly, they can slightly alter the surface and act as an extra barrier - provided they are truly dry.
• Repotting: Replace heavily infested, old, or compacted compost with fresh, structurally stable potting mix.
• Mild soapy solution or diluted hydrogen peroxide: Some plant owners use either one in small, targeted doses, after first testing on a small area.

What you must keep in mind when using matchsticks

Even though the method seems simple, a few rules matter:

• Never light matchsticks before inserting them.
• Store the box out of children’s reach.
• If you have pets, consider covering the compost surface with fine decorative gravel or another mineral material so matchsticks cannot be chewed.
• If you notice a musty smell, severe yellowing leaves, or stalled growth, stop and check the plant.

If you have several pots in one room, treat all affected plants consistently. Otherwise the fungus gnats simply move from pot to pot and the impact remains limited.

A biological approach instead of spray mist: where this method fits

Gardening organisations and specialists are increasingly favouring biological, or at least gentler, solutions for houseplants. Beneficial nematodes, yellow sticky traps, and carefully managed watering are already standard tools.

The matchstick trick sits alongside these as a practical add-on: not a miracle cure, but a simple way to disrupt the fungus gnat life cycle over two to three weeks. Anyone expecting the problem to disappear overnight is likely to be disappointed. Those who stick with it and pair it with better care habits often see noticeably fewer flies after a few days.

When other methods make more sense

For very valuable plants, sensitive species (for example rare orchids), or persistent heavy infestations, it is worth considering alternatives. Beneficial organisms such as certain nematodes are applied via the watering can and target larvae directly. That can also suit households with small children or animals if matchsticks feel like the wrong choice.

A complete compost change can also be sensible if the medium is heavily compacted, mouldy, or has not been renewed for years. It’s a chance to reset drainage, pot size, and watering habits - effectively a fresh start for the plant.

Practical example: basil on the windowsill

A common nursery scenario goes like this: a supermarket pot of basil sits by the sink window, is watered almost daily, and is left standing in water. Before long, touching the pot sends up clouds of tiny gnats.

To bring it under control, professionals often proceed as follows:

• Move the plant into a pot with a drainage hole and a drainage layer.
• Reduce watering - only water again when the top layer looks dry.
• Insert several matchsticks with the heads pointing down around the pot rim.
• Place yellow sticky traps near the plant.

Within a few days, the number of visible fungus gnats usually drops noticeably; after two to three weeks, it typically settles at a stable level.

If you stick to the basics - adjusted watering, free-draining compost, and careful handling of matchsticks - this simple trick can be an effective tool against fungus gnats without immediately reaching for harsh chemicals.