Is my plant overwatered or underwatered?

Why can't you tell from the leaves alone?

The two problems share their main symptoms. University of Maryland Extension says a plant can wilt when it needs water and when it has too much. The Royal Horticultural Society, or RHS, adds that wilting from overwatering is easy to mistake for thirst. The RHS also lists both too much and too little water among the causes of yellow leaves, along with low light and cold. Our guide to yellow leaves covers the rest.

The most confusing case is an overwatered plant that looks thirsty. Water that stays in the pot pushes out the oxygen roots need, so roots die and rot can follow. Damaged roots take up less water, so the plant wilts even though the mix is wet. Adding water at that point can make things worse, as Clemson and Iowa State both warn.

Sources: Watering Indoor Plants; How to help a poorly houseplant; Leaf damage on houseplants; Houseplant Watering Recommendations; Indoor Plants: Watering; Diagnosing Houseplant Problems Related to Poor Culture.

How do you tell overwatered from underwatered?

Run the checks in the table from the top. The first two do not disturb the plant. University of Maryland Extension tests the mix about two inches down, and Iowa State says an inch or two. Succulents and cacti need far less water than most houseplants, so dry mix alone does not mean they are thirsty. If you do not know your plant, identify it first.

Treat the leaves as supporting evidence. Penn State Extension also lists overwatering as a possible cause of yellow older leaves, so sources differ on that pattern. The RHS says dry air can make leaf edges crispy too.

Look at the roots if the mix and the pot disagree or the plant wilts. The University of California IPM program advises inspecting roots whenever wilting occurs. Illinois Extension says healthy roots are generally white, with some exceptions.

Sources: Watering Indoor Plants; Root Rots of Indoor Plants; Root Rots on Houseplants; Diagnosing Houseplant Problems Related to Poor Culture; How to help a poorly houseplant; Diagnosing Poor Plant Health; Houseplant Problems; Keep houseplants happy with simple solutions.

What should you do if the plant is overwatered?

1. Stop watering and pour out any water in the saucer, outer pot or pot base. Check that the pot has a drainage hole.
2. Slide the plant out of its pot and look at the roots. If they look healthy, put it back and let the mix dry at about two inches before you water again.
3. If some roots are brown or black and soft, trim them off. Dry a soggy root ball with kitchen towel. Repot in fresh, well-drained mix, in a pot just big enough for the smaller root system.
4. Keep the repotted plant just moist enough that it does not wilt.
5. Do not reuse the old mix or drained water, because both can carry root rot fungi. Clean your tools and work surface afterward.
6. If the rot is advanced, the plant may not recover. University of Maryland Extension and the University of Wisconsin both support throwing out a badly rotted plant. To keep the variety, take a cutting from healthy tissue.

Sources: Diagnosing Houseplant Problems Related to Poor Culture; Common Problems and Issues of Succulents; Ailing Houseplants; Keep houseplants happy with simple solutions; Watering Indoor Plants; Leaf damage on houseplants; Root Rots on Houseplants; Root Rots of Indoor Plants.

What should you do if the plant is underwatered?

1. Water until it runs out of the drainage holes, so the whole root system gets wet. Then empty the saucer or outer pot.
2. If water rushes down the sides and the mix stays dry, set the pot in a sink or bucket of water. Take it out when the surface is moist, then let it drain completely.
3. If the plant stays wilted while the mix is wet, look at the roots, because a long dry spell can kill roots too.
4. Check the mix before each watering, because each very dry spell injures some roots. Our watering guide covers that routine.

Sources: Houseplant Watering Recommendations; Ailing Houseplants; Indoor Plants: Watering; Watering Indoor Plants.

What if the signs are mixed?

Dry on top, damp lower down. Go by the deeper reading and wait. Iowa State says to hold off when the mix is wet or damp, and to wait at least one more day if you are unsure.

A wet saucer under dry mix. Mix that dries out too far pulls away from the pot. Water then runs down the sides into the saucer and the roots stay dry. This plant is underwatered, so rewet it in a sink or bucket.

Wet mix after a long dry spell. A plant that dried out badly may have lost roots, and the roots left cannot use a soaking. It stays wilted, and more roots can die from lack of oxygen. Stop watering and check the roots.

The mix stays wet even though you rarely water. A pot too big for the root system, a pot with no drainage hole, or old and compacted mix can each keep the roots too wet. Repot to fix the cause.

The mix, pot and roots all look fine. Water may not be the cause. Too much light, heat, cold and fertilizer salts can also make a plant wilt. Our guide to what is wrong with your plant covers other causes.

These checks point to a likely cause and do not prove one. The University of Wisconsin warns that very few plant diseases can be diagnosed accurately by eye.

Sources: Diagnosing Houseplant Problems Related to Poor Culture; Houseplant Watering Recommendations; Ailing Houseplants; Watering Indoor Plants; Houseplant Problems; How to help a poorly houseplant; Diagnosing Poor Plant Health; Root Rots on Houseplants.