How often to water cannabis depends on the plant, not the calendar: water when the pot has become light and the top 2–3 cm of soil are dry. Each time, water until 10–20% drains out of the bottom: roughly a quarter to a third of the pot volume, or about 2.5–3.5 litres for an 11-litre pot. In soil that usually means every 2–4 days; in coco, once or several times a day in smaller amounts.
In brief
- Water by pot weight and a dry surface, not by the calendar.
- Water until 10–20% runs off and empty the saucer after 15–30 minutes.
- Soil: every 2–4 days for a mature plant; coco: daily or several times a day.
- Water at 18–22 °C with the right pH, given in the first hours of light.
- Drooping leaves in a wet growing medium mean too much water, not thirst.
When to water: pot weight and the finger test
The most reliable method is weight. Lift the pot right after a full watering and again when the soil is dry: after a couple of cycles you will feel the difference by hand. In soil, water when about half of the water has been used up; do not let coco get that dry, because it works best when it stays evenly moist.
As a check, push a finger into the growing medium: if the top 2–3 cm are dry, it is time in soil. The surface can look dry while the centre of the pot is still wet, so with large pots the finger test alone is not enough.
How much water: runoff and pot volume
Wet the whole root ball evenly until 10–20% of the water you gave runs out of the bottom. Runoff carries away excess salts and confirms that the medium is wet all the way down. Pour slowly and in two passes a few minutes apart: if the soil is very dry, water runs down the sides of the pot and seems to drain before the centre is wet.
| Pot | Water per watering (dry soil) | Notes |
|---|---|---|
| 0.5–1 l (seedling) | 0.1–0.3 l | a little water around the stem |
| 3 l | 0.75–1 l | small pots dry out quickly |
| 7 l | 1.75–2.3 l | a common size for autoflowers |
| 11 l | 2.5–3.5 l | watch the runoff, not just the litres |
| 20 l | 5–6.5 l | split into 2–3 passes |
The figures in the table are a starting point: the right amount is whatever gives 10–20% runoff. After 15–30 minutes, empty the saucer or use a tray with a drain: the roots must not sit in runoff water. With mineral nutrients, check the pH and EC of the runoff from time to time, as explained in the guide to cannabis pH water.
How often to water: stage and growing medium
Frequency depends on plant size, pot volume, temperature, humidity and light intensity. The values below are typical for an indoor grow at 20–28 °C.
| Stage | Soil | Coco coir |
|---|---|---|
| Seedling (first 2–3 weeks) | every 2–3 days, little water | once a day, small amounts |
| Vegetative stage | every 2–4 days | 1–2 times a day |
| Flowering | every 1–3 days | 1–3 times a day |
Soil holds a lot of water and should partly dry out between waterings, because roots also need air. Coco drains better and should never dry out: give smaller, more frequent amounts, always with nutrient solution. Fabric pots dry out faster than plastic ones.
Too much or too little water: the symptoms
| Sign | Too much water | Too little water |
|---|---|---|
| Leaves | swollen and firm, curling down | limp and thin, hanging with no strength |
| Pot | still heavy after 3–4 days | very light, soil pulling away from the sides |
| Growing medium | always wet, fungus gnats, rotten smell | dry and dusty on the surface |
| After watering | no improvement, growth stalls | the plant perks up within a few hours |
Overwatering is the most common mistake, especially with seedlings in large pots. If the plant droops and the pot is heavy, do not water: wait until it gets lighter and make sure the drainage holes are not blocked. Other causes of curling or drooping leaves are covered in the guide to curling or drooping cannabis leaves.
Temperature, water quality and timing
- Temperature: 18–22 °C. Cold tap water, often below 12 °C in winter, slows the roots; leave it in a container in the room for 12–24 hours.
- Quality: Swiss tap water is fine; what matters is adjusting the pH after adding nutrients: 6.0–7.0 in soil, 5.5–6.5 in coco.
- Timing: in the first hours after lights on, when the plant starts to transpire; avoid watering just before dark, because the medium stays wet for a long time and humidity rises in the grow tent. Outdoors, in the morning.
Automatic watering and time away
For one or two weeks away you need a reservoir and a system that delivers water evenly. A mature plant in an 11–20 litre pot uses roughly 1–3 litres a day in flowering, depending on its size, light, temperature and humidity.
- Measure actual use for 3–4 days by weighing the pot or noting the litres given.
- Choose a reservoir that covers the time away with at least a 30% margin.
- Install a watering system: drip irrigation with a pump and timer, or a gravity system with ceramic probes that release water as the medium dries.
- Test it at least a week before leaving and check that every pot drains.
With drip irrigation, runoff must end up in a tray or container, not on the floor. If you feed, only put mineral products or products suitable for automatic watering in the reservoir: many liquid organic nutrients ferment and clog the drippers.
Frequently asked questions
How often should you water?
When the pot is light and the top 2–3 cm are dry: usually every 2–4 days in soil, daily or more often in coco. Large plants, heat and strong light shorten the interval.
Is it better to water in the morning or the evening?
At the start of the light period, which in a grow tent may well be the evening. Watering just before dark leaves the medium wet and raises night-time humidity.
How much water for an 11-litre pot?
About 2.5–3.5 litres with dry soil, until 10–20% runs off. A freshly transplanted seedling needs far less, poured around the stem.
How can I tell if I have overwatered?
Swollen leaves curling down, a pot that is still heavy after days and a constantly wet medium are the typical signs. Stop watering until the pot gets lighter and check that water drains away.
Containers, pumps and watering accessories are in the Gro.w.LaB Water and irrigation collection.
Updated on 13 October 2026.