How often to water houseplants (and how to tell)

Check first: the finger test

Gardening experts agree on one thing: don't water by the calendar alone. The Royal Horticultural Society says to check that a pot needs water before you water it, and university extension services such as Clemson's point out that the right frequency depends on the plant, its pot, its spot and the weather.

1. Push a finger into the compost, a few centimetres down, near the edge of the pot.
2. Dry at your fingertip? Most leafy plants are ready for water.
3. Still damp? Wait a few days and check again.
4. Lift the pot. A dry pot feels noticeably lighter than a freshly watered one. After a few weeks you'll know by weight alone.

How dry is "dry" depends on the plant. Ferns and calatheas like the compost kept lightly moist, so water when the surface is barely dry. Most foliage plants, such as pothos and monstera, want the top 2 to 5 cm dry. Succulents, cacti, snake plants and ZZ plants should dry out all the way through.

What changes how often you water

• Season. Plants grow and drink most in spring and summer. In autumn and winter, growth slows and pots stay wet for longer, so water less. Central heating can dry pots out faster, so keep checking.
• Light. A plant in a bright window uses water faster than the same plant in a dim corner.
• Temperature. The RHS notes that plants in a cool room need watering less often than those in a warm one.
• Pot size. Small pots dry out quickly; big pots hold water for longer.
• Pot material. Unglazed terracotta dries faster than plastic or glazed ceramic.
• Drainage. A pot with no drainage hole holds water at the bottom, where roots can rot. The RHS says containers should always have one.
• The plant itself. Thick, waxy or fleshy leaves store water. Thin, soft leaves lose it quickly.

Plant Care works these into each plant's schedule. It starts from the species, then waters less often in autumn and winter (and far less for succulents and cacti), adjusts for the light you give it, the pot size and whether the pot drains, and follows your hemisphere. Tap Soil still damp and it waits a little longer next time, and learns.

Watering chart for common houseplants

Use these as starting points for a plant in a medium pot (about 15 cm) with a drainage hole, in the light it likes. They come from the care guide in Plant Care. Always check the compost first.

How to water properly

1. Use room-temperature water. The RHS warns that very cold water can harm plants, especially in winter.
2. Water thoroughly, until water runs out of the drainage hole. A small splash only wets the top and leaves the roots below dry.
3. Let it drain, then empty the saucer. Roots left standing in water can't get air and start to rot.
4. Soak orchids instead. Moth orchids in bark do best when the pot sits in water for 10 to 15 minutes and then drains well.
5. Mind hard water for fussy plants like calatheas, which can get brown edges. Filtered or rainwater helps. Never use water from a domestic water softener: the RHS says the salts in it are harmful to plants.

Overwatered or underwatered?

Both can make a plant wilt, which is why people often water a drowning plant even more. Check the compost before you act. These signs follow the RHS guide to poorly houseplants.

To rescue an overwatered plant, tip it out of its pot, pour away any trapped water, trim soft or rotten roots and dead leaves, and repot into fresh, free-draining compost. Then water less often. To revive a dry plant, water it thoroughly, or stand the pot in water for half an hour if the compost has shrunk away from the sides, then let it drain.

A note on pets

Several of the easiest houseplants are toxic to cats and dogs if chewed, including pothos, monstera, peace lily, snake plant, ZZ plant, aloe and jade. Spider plants, Boston ferns, calatheas and moth orchids are generally considered non-toxic.

Check any plant against the ASPCA's toxic and non-toxic plant lists. Plant Care's guide follows those lists and marks plants that aren't on them as unknown, never as safe. If you think your pet has eaten a plant, contact your vet straight away.

Common mistakes

• Watering every plant on the same day. A fern and a cactus have very different needs.
• Keeping the summer routine in winter. Wet, cold compost is a common route to root rot.
• Little sips every day. Water thoroughly and less often instead.
• Pots with no drainage hole. Use a plastic pot with holes inside a decorative one, and empty it after watering.
• Reading every droop as thirst. Feel the compost first.