More first plants die of water than of anything else, and almost always too much of it, not too little. There's no schedule that works — a plant's need changes with its size, the pot, the light, the temperature and the week — so this guide is about how to tell, which is a skill that takes about a fortnight to learn and then never leaves you.
Why overwatering kills
Roots need oxygen as much as water. A pot that's kept wet has no air in it; the roots suffocate, stop taking up water and nutrients, and start to rot. The plant droops — which looks like thirst — so the natural response is more water, which finishes the job. If a drooping plant has a heavy, wet pot, it's drowning, not thirsty.
Underwatering, by contrast, is loud and quick to fix: the plant wilts dramatically, you water, it perks up within an hour. It's very hard to kill a plant by underwatering it once.
The method: water by weight
- Water the pot thoroughly once, until it runs from the bottom. Lift it. That's "full" — remember the weight.
- Every day, lift it. Don't water.
- When it feels roughly half as heavy as full — noticeably light, the way an empty kettle feels — water it again, thoroughly, to runoff.
That's the whole technique. The interval takes care of itself: a seedling in a 3-gallon pot might go a week; a big plant in flower under a strong light might need water every day or two. You never have to know the number, because the pot tells you.
A finger pushed two inches into the mix is the backup check: dry at that depth means water; damp means wait. The surface is not a guide — it dries hours before the root zone does.
How much: always to runoff
When you water, water until 10–20% runs out of the bottom. Two reasons. Little sips wet the top of the pot and leave the bottom dry, so roots grow upward into a shallow layer and the plant is never properly hydrated. And runoff carries out the salts left behind by the last feed — without it they accumulate until the plant burns. Water slowly, in two passes a few minutes apart, so the mix wets evenly instead of channelling straight through. Then empty the saucer. A pot standing in its runoff is a wet pot again.
The exceptions to "let it dry"
- Coco coir should never dry out completely — it goes hydrophobic and is hard to re-wet, and dry coco locks out calcium. Water coco when it's lighter, not light: at roughly two-thirds weight rather than half, and daily is normal for a plant of any size.
- Seedlings and cuttings have tiny roots and want the top inch kept moist, in a small pot or cup — never a big pot, which stays wet for weeks around them. Move them up in pot size when roots show at the drainage holes.
- Hydro is a different subject; the roots live in oxygenated water and the concern is the reverse.
When in the day
At lights-on, or just after. The plant drinks most during the light period, and a pot watered in the morning dries through the day. A pot watered at lights-off sits cold and wet all night, which is how humidity climbs and mould starts — see Grow tent temperature and humidity.
What the water should be
- Temperature: room temperature, 65–75 °F. Cold water shocks roots and slows growth; warm water carries less oxygen.
- pH: adjusted every time if you're feeding minerals — 6.0–6.8 in soil, 5.8–6.2 in coco. Plain-water days too; tap water is often above 7.
- Chlorine: an hour standing in an open jug deals with it. Chloramine doesn't gas off but is harmless at tap levels.
- Feed: on feed days, mix the nutrients first, then adjust pH, then water. The routine is in How to use nutrients properly.
Reading the plant
| What you see | Pot weight | What it means | Do |
|---|---|---|---|
| Drooping, leaves soft | Heavy, wet | Overwatered | Stop. Let it dry to half weight. Improve airflow. |
| Drooping, leaves limp and thin | Light, dry | Underwatered | Water to runoff; it recovers in an hour |
| Drooping, leaves curled down and firm | Either | Heat or light stress, not water | Check tent temperature and light distance |
| Yellowing bottom leaves, pot always wet | Heavy | Roots suffocating — looks like nitrogen deficiency | Dry out first; don't feed |
| Water pooling on top, running down the sides | Light | Mix has gone hydrophobic | Water slowly in several passes; a drop of dish soap in a gallon helps it re-wet |
The pots and mix that make it easy
Fabric pots dry from all sides and are very hard to overwater; a free-draining mix with 20–30% perlite has air in it even when wet. Between them they turn watering from a judgement call into something you can learn by feel in a week. Sizes and the reasoning are in Fabric pots vs plastic.
The one-line version
Water thoroughly to runoff, then not again until the pot is half its full weight — every day lift it, most days don't water it. Morning, room temperature, pH adjusted. Empty the saucer. That's it.
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