Bottom watering means setting a pot in a container of water and letting the soil draw moisture up through the drainage hole, instead of pouring water in from the top. It’s not necessary for every plant, but for a handful of common problems — fungus gnats, soil that repels water, plants with rot-prone crowns — it solves the underlying issue better than top watering does.

How to do it

1. Fill a sink, tray, or basin with a few inches of room-temperature water — enough to reach partway up the side of the pot, but not so much that it spills over the rim.
2. Set the pot in the water and let it sit. Capillary action draws water up through the drainage hole and through the soil from the bottom.
3. Wait until the top of the soil feels damp, usually somewhere between 15 minutes and an hour depending on pot size and how dry the soil started out. Check periodically rather than guessing a fixed time.
4. Remove the pot and let it drain fully before setting it back on a saucer or in a decorative cover pot. Skipping this step just moves the standing-water problem from the top of the soil to the bottom of the pot.

Why it works better for some plants

It prevents water from sitting in a plant’s crown or rosette. Plants like African violets and bird’s nest fern are prone to crown rot if water pools where their leaves emerge from the center. Bottom watering avoids that entirely since the water never touches the top of the soil or the plant itself.

It discourages fungus gnats. Gnat larvae live in the top inch or two of consistently damp soil, and top watering keeps that layer wet every time you do it. Bottom watering leaves the surface drier even as the root zone gets adequately moist, which makes the top layer less hospitable for gnats to breed in. See how to get rid of fungus gnats if you’re already dealing with an infestation — bottom watering going forward helps prevent a repeat.

It rewets soil that’s become hydrophobic. Potting mix that’s dried out completely, especially mixes heavy in peat, can start to repel water rather than absorb it — you’ll see water run straight down the inside edge of the pot and out the bottom without actually soaking into the soil. Bottom watering forces water to soak in from underneath, rehydrating mix that top watering would otherwise just run past.

It waters more evenly. Top watering can leave dry pockets if the water finds a path of least resistance down one side of the root ball, especially in a pot that’s been allowed to dry out completely. Soaking from the bottom pulls water evenly through the whole volume of soil.

When top watering is still the better choice

Bottom watering isn’t a universal upgrade. It doesn’t flush accumulated fertilizer salts out of the soil the way top watering does, since nothing is running through and out the drainage hole — plants watered this way exclusively benefit from an occasional top watering flush to clear salt buildup. It’s also slower and less practical for a large collection, and it doesn’t work for pots without drainage holes, which need a different approach in the first place — see self-watering pots explained for one alternative. For most plants, either method works fine; use bottom watering selectively for the specific problems it solves rather than switching your entire routine over.

A few practical notes

Use room-temperature water rather than cold water straight from the tap, since cold water can shock roots the same way it would with top watering. If you bottom water multiple plants in the same basin, be cautious about reusing that water for a plant that might have a pest or disease issue, since it’s possible to spread problems between pots that way. For the general principles behind judging how much and how often to water in the first place, see watering houseplants the right way.