How to Bottom Water Plants (and Why to Top Water Too)

The Lab | How to Bottom Water Plants

Bottom watering means letting a pot drink from below: you set it in a saucer or bowl of water and the dry potting mix pulls water up through the drainage holes. University of Maryland Extension defines it simply as putting water into the saucer or setting the container in a pot of water. This guide covers how to bottom water plants step by step, when it helps, and the one thing most bottom-watering guides leave out: salts.

The verdict Set the pot in about an inch of room-temperature water, take it out once the soil surface feels moist, let it drain, and never leave it standing in water. Bottom watering is handy for plants whose leaves should stay dry, such as African violets, and for mixes that have dried out and shrunk. But it does not flush salts: Colorado State Extension warns it can build up salts in and on the surface of the soil, so water thoroughly from the top every so often.

How to Bottom Water Plants, Step by Step

Check that the plant needs water. Maryland Extension says to water when plants need it, not on a schedule, and to check whether the mix is dry about two inches down. Colorado State Extension adds that plants preferring even moisture can be watered when the top layer starts to feel dry, while plants that like to dry out should be checked deeper.
Use a pot with drainage holes. Water can only wick up through the holes.
Fill a bowl, sink or tray with room-temperature water. The University of Minnesota Extension African violet guide describes about 1 inch of room-temperature water.
Set the pot in and wait until the surface of the mix feels moist.
Lift it out and let it drain. Then empty any water left in the saucer. Both Maryland and Colorado State Extension stress the same rule: never let houseplants sit in water.

How Bottom Watering Works

Dry potting mix acts like a sponge. Standing in shallow water, it draws moisture upward through the drainage holes until the root zone is wet. That is why bottom watering works well on a pot whose mix has dried and pulled away from the sides: water poured on top of shrunken, dry mix can run down the gap and out of the pot without wetting the roots, while a soak from below rewets the whole root ball.

Because the surface is not drenched each time, bottom-watered pots also tend to have a drier top layer. That can help with fungus gnats, which the UC Statewide IPM Program says thrive in moist conditions; UC IPM recommends letting the surface of container soil dry between waterings. See our fungus gnat guide for more.

When Bottom Watering Helps

Plants whose leaves should stay dry. Minnesota Extension notes that water on African violet leaves can cause leaf spots, and lists bottom watering (along with careful top watering and wicking) as a way to water them.
Dried-out, shrunken root balls. A soak from below rewets mix that sheds water from the top.
Small pots and seedlings that a watering can would disturb.
Several small pots at once, set together in one tray.

It is less practical for large floor plants, and it is unnecessary in self-watering pots, which already supply water from below (see our self-watering pot guide).

How Long to Leave Plants in Water

There is no fixed time; watch the soil, not the clock. Minnesota Extension’s rule is to remove the pot when the soil surface feels moist. Small pots in a light mix may take only a few minutes; large pots, very dry mix or chunky bark mixes take longer. If the surface is still dry after a long soak, the mix may be very compacted or water-repellent: water it from the top as well, or repot into fresh mix.

Do not leave pots soaking for hours or overnight. Colorado State notes that most plants do not tolerate waterlogged soil, and constantly wet mix is the classic route to root rot.

Common Mistakes and Fixes

Mistake	Why it hurts	Fix
Leaving the pot standing in the tray	Waterlogged mix; roots run short of air	Remove when the surface is moist, drain, empty the saucer
Only ever bottom watering	Salts accumulate in and on the surface of the mix (Colorado State)	Water thoroughly from the top now and then so water runs out of the holes
Watering on a fixed schedule	Water needs change with light and season	Check the mix first, as Maryland Extension advises
Using softened water	Maryland Extension says softened water should be avoided for houseplants because of its salt content	Use unsoftened tap water, rainwater or filtered water
Assuming a moist surface means a wet root ball in a huge pot	The center of a large root ball can stay dry	Lift the pot: a well-watered pot feels noticeably heavier

Sources: Colorado State Extension PlantTalk 1318; University of Maryland Extension.

Bottom watering does not flush salts

Colorado State Extension says subirrigation can lead to an accumulation of excess soluble salts in and on the surface of the soil, and recommends periodically watering from the top to leach them. The usual sign is a whitish crust on the soil or the rim of the pot. Maryland Extension suggests leaching with at least twice the pot’s volume of water every four to six months. If you already have a crust, see our white crust guide.

Bottom watering also cannot save a plant whose roots are already rotting. If stems are soft and roots brown and mushy, deal with the roots first.

Bottom Watering vs Top Watering

	Bottom watering	Top watering
Keeps leaves dry	Yes	Only if you water carefully at soil level
Rewets dried, shrunken mix	Well	Water may run down the sides
Flushes salts	No; can build them at the surface	Yes, when water runs out of the holes
Time	Slower; pots must soak and drain	Faster
Extension view	Colorado State calls top watering generally better than subirrigation; use bottom watering where it helps and flush from the top periodically

Sources: Colorado State Extension; University of Minnesota Extension; University of Maryland Extension.

The practical answer for most collections is to use both: bottom water the plants that benefit, and give every pot a thorough top watering from time to time. For more on how often to water, see our overwatered vs underwatered guide.

For more on repotting and potting mix, see our guides to how to repot a plant.

Key takeaway To bottom water plants, stand the pot in about an inch of room-temperature water, remove it when the surface is moist, drain it, and never leave it sitting in water. It suits dry-leaf plants like African violets and dried-out root balls, but it can build salts at the surface, so leach every pot from the top every few months.

Frequently Asked Questions

How long should you bottom water plants?

Until the surface of the potting mix feels moist, then take the pot out, as University of Minnesota Extension advises. Small pots can take a few minutes; large or very dry pots take longer. Do not leave them soaking for hours.

Is bottom watering better than top watering?

Not in general. Colorado State Extension says top watering is generally better than subirrigation because bottom watering can build up salts. Bottom watering is useful for plants whose leaves should stay dry and for rewetting dried-out mix.

How often should you bottom water?

Whenever the plant needs water, not on a schedule. Check the mix first: Maryland Extension suggests feeling about two inches down.

Do you need to top water if you bottom water?

Yes, occasionally. Colorado State recommends periodically watering from the top to leach salts that build up with bottom watering, letting water run out of the drainage holes.

Can you bottom water succulents?

Yes. Soak until the mix is moist, drain fully, and let the mix dry out well before the next watering. See our succulent guide.