GrowSabzWatering calculator
How much water does your plant need? Choose the plant, your container and today's weather. You get the answer in millilitres — scaled to the pot you actually have, not a generic rule.
Choose a plant to begin.
How the watering amount is worked out
Every plant in the database carries a base water requirement expressed per 10 litres of soil, plus separate watering intervals for normal, hot and cool weather. Scaling that to your own container is straightforward:
water = base per 10 L × (your litres ÷ 10) × container multiplier
The container multiplier is the part most guides leave out. A fabric grow bag breathes through its walls, so it dries faster than a plastic pot of the same volume and carries a higher multiplier. Open ground draws on the surrounding soil and carries a lower one. Same plant, same volume, genuinely different amounts of water.
Why "water regularly" is useless advice
Most growing guides stop at "keep the soil moist". That shifts the entire judgement onto you, and it is the single most common reason container plants fail — not neglect, but a watering can used with no sense of scale.
A 20 litre pot of bitter gourd wants around 2.4 litres a day in summer. A 20 litre pot of rosemary wants a small fraction of that, far less often. "Regularly" covers both and helps with neither.
How often should you water — by container type
The same plant in the same volume of soil dries at very different rates depending on what is holding it. Roughly:
| Container | Dries | What to watch |
|---|---|---|
| Fabric grow bag | Fastest | Evaporates through the walls as well as the surface. In summer heat these can need water twice a day once the plant fills the bag. |
| Plastic or glazed pot | Moderate | Only the surface evaporates. Drainage holes matter more here than anywhere else — without them the base stays saturated. |
| Terracotta pot | Fast | Unglazed clay is porous and wicks moisture out through the sides. Good for herbs that hate wet feet, demanding for thirsty crops. |
| Raised bed | Slow | Large soil volume buffers against both drought and your mistakes. Water deeply and less often. |
| Open ground | Slowest | Roots reach beyond the watered zone and draw on subsoil moisture. Established plants can go a long time between waterings. |
Overwatering and underwatering look almost identical
This catches nearly everyone at least once. Both produce wilting, both produce yellow leaves, and the instinctive response to a wilting plant is to water it — which, if the problem was too much water, kills it faster.
The difference is in the detail:
- Underwatered — leaves wilt but stay firm and dry to the touch, the soil pulls away from the sides of the pot, and the plant recovers within hours of being watered.
- Overwatered — leaves yellow from the bottom up, feel soft or limp rather than crisp, the soil smells sour, and watering makes it worse. Roots are brown and mushy instead of white and firm.
When you are unsure, stop watering and check the soil at depth. Dry soil is a problem you can fix in an afternoon. Root rot is a problem you often cannot fix at all.
When to water matters as much as how much
Water in the early morning wherever you can. The plant takes up what it needs before the heat of the day, and the leaf surfaces dry quickly, which gives fungal disease far less opportunity than an evening soaking does.
Water the soil at the base, not the foliage. Wet leaves spread exactly the diseases you are trying to avoid, and water that lands on leaves largely evaporates before reaching the roots.
Water deeply and less often rather than lightly and daily. A light sprinkle wets the top few centimetres and encourages roots to stay shallow, where they are most vulnerable to heat. A thorough soak until water runs from the drainage holes drives roots downward.
What the number cannot know
- Your soil mix. Heavy, compost-rich mixes hold water much longer; sandy or very open mixes drain fast.
- Wind. A windy balcony dries pots considerably faster than a sheltered yard at the same temperature.
- Plant size. A mature fruiting plant drinks several times what a seedling in the same pot does.
- Humidity. The same temperature in dry and humid air produces very different evaporation rates.
So treat the figure as a calibrated starting point, then check the soil. Push a finger in to the second knuckle — if it is dry at that depth, water; if it is damp, wait a day.
Common questions
How much water does a tomato plant need per day?
A tomato in a 20 litre pot needs roughly 1.9 litres each time you water, about every two days in normal weather — around 6.7 litres a week. In hot weather that becomes daily. Select tomato in the calculator above to see the figure for your own container size.
How often should you water potted plants?
It depends far more on the plant than on a general rule. Fast-growing fruiting vegetables in containers often need water every day in summer; woody herbs like rosemary can go several days. The interval in the calculator comes from each plant's own recorded requirement, adjusted for hot and cool weather.
Should I water my plants every day?
Only if the plant and the container call for it. Watering on a fixed daily schedule regardless of conditions is one of the most common causes of root rot in pots, because the roots never get the air they need between waterings. Check the soil first: push a finger in to the second knuckle, and water only if it is dry at that depth.
Do plants in grow bags need more water than pots?
Yes. Fabric grow bags breathe through their walls, so they dry out noticeably faster than a plastic pot of the same volume. The calculator applies a per-container multiplier for exactly this reason — select the container you actually use and the figure changes.
How much water do plants need in winter?
Considerably less. Growth slows, evaporation drops and the soil stays wet far longer. Switch the weather selector to "Cool" and the interval stretches accordingly. Overwatering kills more container plants in winter than cold does.