Why palm soil stays wet
Updated: October 2026
You repotted at the weekend, the pot is still heavy on Wednesday, and a cloud of tiny flies lifts off when you water. Palm soil stays wet for three ordinary reasons: the mix is fine, the pot is standing in its own runoff, or you gave the roots a tub of unused compost. The bag is sometimes part of it. Volumes and prices are on the [palm soil comparison](/hub/trees-and-palms/palm-soil). We did not treat a plant. A qualifying purchase can earn us a commission at no extra cost to you.
You repotted at the weekend, the pot is still heavy on Wednesday, and a cloud of tiny flies lifts off when you water.
You repotted at the weekend, the pot is still heavy on Wednesday, and a cloud of tiny flies lifts off when you water. Palm soil stays wet for three ordinary reasons: the mix is fine, the pot is standing in its own runoff, or you gave the roots a tub of unused compost. The bag is sometimes part of it. Volumes and prices are on the palm soil comparison. We did not treat a plant. A qualifying purchase can earn us a commission at no extra cost to you.
Our top picks
| Badge | Product | Drainage on the listing | Volume | Flies in UK reviews | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  Invigortex Invigortex houseplant mix, 3 litre title | Fast-draining claim, no rate | Title 3 litres, spec 1 litre | One shared review, no flies | 5.5 | about £8.99 | View offer |
 COMPO COMPO Sana palm compost, 10 litres | Some perlite; UK buyer added more | 10 litres, lines agree | UK reviews report flies and none | 9.2 | about £26.84 | View offer | |
| Best value |  COMPO COMPO Sana palm earth, 5 litres | Reviews describe a wet mix | 5 litres, lines agree | One review mentions baking | 8.6 | about £20.59 | View offer |
On this page
Why palm compost stays wet
A palm in a pot fails when the roots sit in water. Water leaves through holes, grit and empty saucers, not through the word palm on the label. COMPO’s bullets say a lot of water and publish no drainage rate. Invigortex says the mix is fast-draining and gives no grit percentage. Your pot on day three is the test.
If the saucer is full, empty it. A cover pot with no hole is the same puddle. Twenty minutes after watering, tip away what ran through.
A ring of fresh mix with no roots in it stays wet. A parlour palm wants only a couple of centimetres more width. A jump from 12 cm to 25 cm will still be wet on Wednesday. Do not repot again this week. Width and timing are on how to repot a palm.
One review of the COMPO 5 litre bag describes the compost arriving wet, with pieces of wood. Let the bag air with the top folded closed. That is not a reason to bake it.
Grit, and what a review added
Where you only need air, the RHS prefers grit or gravel. Coarse sand is the indoor-palm option. A UK buyer of the COMPO 10 litre bag, at £26.84, found some perlite and added orchid bark and more perlite. The listing never gave a drainage rate.
For Chamaedorea the RHS picture is about three parts compost to one part grit. A kentia mix that already feels open needs less. Wet a handful: paste gets grit, crumbs can go in the pot. Do not add builders’ sand. Which indoor palm wants which mix is on compost for an indoor palm.
Mix grit through the compost, not as a gravel layer in the bottom, which can perch water higher up. Invigortex claims the blend already drains, and every specification line still says 1 litre. If the handful test slumps, you add grit anyway.
Fungus gnats without cooking the compost
The tiny flies are usually fungus gnats, which the RHS describes in damp organic compost. Adults are mostly a nuisance. Larvae can harm seedlings. An established palm is not a seedling. A surface that never dries will keep producing them. Gardeners’ World puts the larvae in the top 5–8 cm.
Let the top dry. A 1 cm grit mulch makes that layer less attractive. Yellow sticky traps catch adults. Keep spare bags sealed, and do not bring homemade garden compost indoors. Gardeners’ World mentions nematodes. Follow the packet. This page does not set a rate.
Do not microwave or bake the compost. Reviews of these bags mention it. Hot compost in a kitchen is a burn risk, and it is not the method. One Invigortex review reports no tiny flies, and the same text sits on three pack sizes. COMPO’s 10 litre UK reviews include both no bugs and flies, including three bags full of bugs and plants lost.
When wet roots are more than a watering mistake
Waterlogged compost and Phytophthora root rot are hard to tell apart at home. Both can leave a heavy pot, a plant that wilts, and a base that softens. You will not diagnose the pathogen from the kitchen.
If the fronds are merely dull, empty the saucer and wait until the top few centimetres change colour. A skewer that comes out wet means wait. If the crown is collapsing, or the base of the stem is soft, stop tinkering with grit. A pot you cannot lift safely is the same stop.
Replacing the compost on a sick plant is a rescue, not the routine repot. Where you can wait for early spring, wait. Where the base is already soft, tell a nursery how long the pot has stayed heavy, whether flies are present, and whether the stem base yields under a finger.
Common questions
Should I add grit or perlite?
Add horticultural grit or gravel when the only problem is air. That is the RHS preference. Perlite is what a UK COMPO buyer added, with orchid bark, after finding the bag’s own perlite thin. Mix it through the compost. A gravel layer in the bottom does not replace drainage holes.
Are the tiny flies from the bag?
They can be. Fungus gnats breed in damp organic compost, and UK reviews of the COMPO 10 litre bag report both flies and none. An open stored bag will keep them going even if the sack arrived clean. One shared Invigortex review reports no flies. That does not prove the product is sterile.
Will fungus gnats kill an established palm?
Adults are mostly a nuisance. The RHS says larvae can damage seedlings, and a mature palm is unlikely to be killed by a light cloud of flies. A compost that stays saturated can still rot the roots. Treat the wet pot as the main problem. Nematodes are a Gardeners’ World option. Follow the packet. This page does not set a rate.
Is a soft base root rot or just waterlogging?
You often cannot tell at home. Waterlogging is the one you can reverse while the crown is still firm. A soft stem base or a collapsing crown is past a compost tweak. Phytophthora is an RHS-described root rot in wet conditions. Stop watering, do not bake the soil, and ask a nursery if the base has gone.
Should I bake or microwave the compost?
No. Reviews of these bags mention baking and microwaving to kill gnats. That is not RHS advice. You risk burns and a ruined mix. Let the surface dry, seal leftover bags, use a 1 cm grit mulch, and empty saucers.
Related pages
Sources
Public UK sources listed below, used for this page in October 2026. Prices, stars and review counts are from the amazon.co.uk listings in this comparison. This is not a laboratory test.
- RHS, Indoor palms (retrieved October 2026)
- RHS, Hardy palms (retrieved October 2026)
- RHS, Chamaedorea growing guide (retrieved October 2026)
- RHS, Peat-free compost choices (retrieved October 2026)
- RHS, Fungus gnats (retrieved October 2026)
- GOV.UK, Sale of horticultural peat to be banned (retrieved October 2026)
- TheyWorkForYou, written answer 19 March 2026 (retrieved October 2026)
- BSI, PAS 100:2018 composted materials (retrieved October 2026)