Watering by the plant, not by the calendar
"Water every Sunday" is how most houseplants die: once a week is far too often for a succulent and not nearly enough for a fern in a sunny window. Soil dries at a rate set by five things — the plant, the pot, the season, the light and the room — and once you can estimate that rate, watering stops being a guessing game.
The five factors
- The plant. Succulents and cacti store water and want to dry out completely; ferns and calatheas come from the jungle floor and never want to dry out at all. That is a four-fold difference in how often you water.
- The pot. Volume matters more than diameter: a 20 cm pot holds about 6 litres of soil, so it stays moist roughly twice as long as a 15 cm pot. Terracotta and fabric pots wick moisture through their walls and dry fastest; glazed ceramic holds it longest.
- The season. In winter, light drops and most plants stop growing. Growth slows, so water use drops by a third or more — the single most common cause of winter root rot is watering at summer frequency.
- The light. A plant in direct sun transpires several times faster than one in a dim corner. More light means more water, and also more growth.
- The room. Warm air and dry heating season air pull water out of the soil; every 5 °C above 20 °C shortens the interval by roughly 10%, and air conditioning dries it out just as fast.
How much to give
Not a splash: water until it runs out of the drainage holes, then tip the saucer away. That flush pushes old salts out of the soil and wets the whole root ball instead of just the top. A useful estimate is 15–25% of the soil volume — about a litre for a 20 cm pot — and that is what this calculator reports. For beds, think in depth instead: 2.5 cm (1 in) of water soaks the top 15–20 cm of soil, which is where most roots live.
Typical intervals to sanity-check against
| Plant | Typical interval (growing season) |
|---|---|
| Snake plant / ZZ plant | 2–3 weeks |
| Succulents, cacti | 2–3 weeks |
| Pothos, philodendron | 7–10 days |
| Monstera, rubber plant | 7–10 days |
| Peace lily | 5–7 days |
| Ferns, calathea | 2–4 days |
| Orchid (bark) | 7–10 days |
| Basil, mint (sunny) | 2–3 days |
Treat these as reference points, then adjust for your own room: if the soil is still damp at the suggested interval, wait two more days; if the plant wilts before it, shorten the interval.
Signs you are getting it wrong
Overwatered: yellowing lower leaves, soft brown patches, fungus gnats, soil that smells sour. Underwatered: crispy brown tips, leaves curling inwards, soil pulling away from the pot wall, and a plant that wilts in the afternoon and recovers overnight. When in doubt, underwatering is the safer mistake — almost every plant survives a missed week, and few survive months of soggy roots.
Frequently asked questions
How often should I water my houseplants?
It depends on the plant, not the calendar: succulents and cacti every 2–3 weeks, most tropical foliage every 7–10 days, ferns and calatheas every 2–4 days, and orchids in bark about weekly. Use those as reference points, then adjust for your pot size, light and season.
How much water should I give a potted plant?
Water until it runs out of the drainage holes, then empty the saucer — roughly 15–25% of the soil volume, which is about a litre for a 20 cm pot. Giving a small splash more often only wets the top layer and encourages weak, shallow roots.
Should I water less in winter?
Yes, substantially. Light levels drop and most plants stop growing, so water use falls by a third or more. Watering at summer frequency in winter is the single most common cause of root rot, and it is why so many houseplants die in January rather than July.
Do terracotta pots dry out faster?
Much faster. Unglazed clay and fabric grow bags wick moisture through their walls, so they can dry out in half the time of a glazed or plastic pot of the same size. That is a feature in summer, when it helps prevent waterlogging, and a nuisance in winter.
How do I know if I am overwatering?
Yellowing lower leaves, soft brown patches, fungus gnats, soil that smells sour and a pot that feels heavy for days after watering. Check by pushing a finger 1 in into the soil: if it is still damp, skip the watering entirely, whatever the schedule says.
How much water does a garden bed need?
About 2.5 cm (1 in) of water per watering, which soaks the top 15–20 cm of soil where most roots are — that is 25 litres per square metre. Water in the morning so the foliage dries before evening, and mulch 5 cm deep to cut evaporation by a third or more.