Am I overwatering or underwatering?

The short answer

Water it, and watch what happens over the next hour or two.

A thirsty plant perks back up. A drowned one does not — because more water is the thing it already has too much of.

That is the whole test, and it works because the two conditions look the same from the outside and behave completely differently the moment you add water.

Why both look like drooping

A leaf holds itself up with water pressure. Lose that pressure and it sags. So anything that interrupts the water supply produces the same limp, heavy-looking plant — which is why the two most common causes in growing are also the two most easily confused.

Underwatering is the simple case: there is no water in the medium to take up.

Overwatering is the one people find counter-intuitive, because the plant is drooping while surrounded by water. Roots are not straws. They need oxygen to do the work of taking water up, and that oxygen lives in the air gaps between particles of your medium. Fill every gap with water and the root can no longer draw. The plant wilts in a pot that is soaking wet, and the grower — reasonably — concludes it is thirsty and waters it again.

That loop is how a plant gets worse for a week under attentive care.

The habit that makes this a non-question

Lift the pot.

Get a feel for what it weighs right after a full watering and what it weighs when the plant is genuinely ready for more. After a few cycles you will know by hand, in a second, without a meter and without guessing. It is the cheapest skill in growing and almost nobody is taught it.

Poking a finger into the top inch tells you much less than you would think, because the top dries first and the bottom of the pot — where most of the roots are — can still be saturated.

I should be straight that this is my own practice and the practice of most growers I have read, not something I am citing a paper for.

	Underwatered	Overwatered
Pot weight	Light	Heavy
After watering	Recovers within an hour or two	No change, or worse
Leaf feel	Thin, papery, sometimes crisp at the edges	Full and heavy, curling downward
How fast	Over a day, and it repeats on a cycle	Over days, and it does not let up

When it is neither, and the root zone is actually sick

There is a third case that begins as chronic overwatering and turns into something else, and it is worth knowing the shape of it.

A waterlogged, airless root zone is the condition several root pathogens prefer. The reference text for the field describes what they leave behind: roots that have gone soft and discoloured, the fine feeder roots simply missing, and in some cases a darkened, sunken area at the base of the stem. The plant wilts in wet medium, which is the same top-level symptom as plain overwatering — the difference is in the roots and the crown, not the leaves.

So if a plant has been wilting in wet medium for a while and letting it dry back has not turned it around, look at the roots. Healthy ones are firm and pale and there are lots of fine ones. That chapter also notes that more than one organism produces this picture and that they do not all want the same response, so “it is root rot” is a start rather than an answer.

What would show that I have this wrong

If the plant recovers overnight without being watered, it was neither — that is a heat-and-light pattern and the plant was simply outrunning its supply during the brightest hours. That case is here. And if the droop comes with colour changes that sort by leaf age, the water may be a side story: start with the pattern.

Where my device fits, stated narrowly

It doesn’t, on this one, and I would rather say so than stretch. Croplock reads the air and the leaf surface; it does not have a sensor in your medium, so it cannot tell you what your root zone is doing. The pot in your hands is the better instrument here and it is free.

Sources

• Cannabis in Controlled Environment Production (CRC Press). DOI 10.1201/9781003150442 — the disease chapter’s account of root and crown rots, the conditions that favour them, and the root and crown signs that distinguish them from simple overwatering.
• The perk-up test and the pot-weight habit are my own practice and are stated as such, not as findings from the literature.

More of these at Answers. The device is at croplock.com.