How often to water houseplants: the finger test and signs of over- or under-watering

TUREFF• •0

Ask how often to water a houseplant and the honest answer is: when it needs it, not on a fixed day. Pot size, soil, light, temperature and the season all change how quickly a plant uses water. Overwatering kills far more houseplants than neglect, so learning to check before you water is the single most useful habit.

Why a calendar does not work

A plant in a small pot on a sunny windowsill in summer might need water every few days. The same plant in a big pot in a dim room in winter might go two or three weeks. Watering by the calendar ends up drowning plants in the slow months.

How to tell when a plant needs water

Finger test: push a finger into the compost up to the second knuckle. For most leafy houseplants, water when the top few centimetres feel dry. Moisture-lovers such as ferns and calatheas like to be watered a little sooner; succulents and cacti should dry out almost completely.
Lift the pot: pick it up just after watering and again when it is dry. You will soon feel the difference in weight.
Look at the soil: dry compost is usually lighter in colour and may pull away from the pot's edge.
A wooden skewer pushed deep into a large pot comes out damp or clean, like testing a cake.
Moisture meters exist, but they are only a rough guide; your finger is free and surprisingly reliable.

How to water

When the plant needs water, water thoroughly until water runs out of the drainage holes, so the whole root ball gets wet. Then let it drain and empty the saucer or decorative outer pot within half an hour or so. Roots sitting in a puddle are the main cause of rot. Little sips every day keep the surface wet while the lower roots stay dry, or stay wet constantly, depending on the pot. Water less often, but properly. Some plants, like African violets, dislike water on their leaves, so pour onto the compost or water from below by standing the pot in a tray for a while, then letting it drain.

Pots and soil matter

Drainage holes are essential. If a decorative pot has none, keep the plant in a plastic nursery pot inside it and lift it out to water.
Terracotta is porous and dries faster than plastic or glazed ceramic.
A pot much bigger than the root ball holds water the roots cannot reach, which stays wet for a long time.
Heavy, compacted compost holds water; a looser mix drains faster. Gravel in the bottom of a pot does not improve drainage and can actually make the wet zone sit higher.

Seasons change everything

Most houseplants grow actively in spring and summer and slow down in autumn and winter, when days are shorter. Expect to water much less in the darker months. Radiators can dry out pots near them, so check rather than assume.

Signs of overwatering

Yellowing lower leaves and soft, limp stems
Compost that stays wet for many days, or smells sour
Mould on the surface or fungus gnats flying around
Brown, mushy roots when you slide the plant out (healthy roots are usually firm and pale)
Wilting even though the soil is wet, because damaged roots cannot take up water

If you suspect overwatering, stop watering, empty any standing water and let the compost dry. Badly rotted plants may need trimming of dead roots and repotting into fresh, drier compost.

Signs of underwatering

Drooping that recovers quickly after a drink
Crisp, dry leaf edges or tips, and leaves curling
Compost shrinking away from the sides of the pot
Water running straight through without soaking in

Very dry compost can repel water. Stand the pot in a bowl of water for 20 to 30 minutes so it rehydrates from below, then let it drain. Which of your plants is hardest to get right? Ask your watering questions or share what works for you in the comments.