How to Water Houseplants

More houseplants die from too much water than from too little. That surprises people, because watering feels like care, and a plant that is struggling seems to need more of it. But roots need air as well as water. Soil that stays wet for days pushes the air out, the roots begin to rot, and a rotting plant wilts in a way that looks exactly like thirst. So it gets watered again.

The good news is that watering well is a skill, not a talent, and it comes down to two questions: does this plant need water now, and if so, how much?

Water by the soil, not the calendar

The most common advice on plant labels, water once a week, is the source of most problems. How fast a pot dries depends on the plant, the size of the pot, what it is made of, the light, the temperature and the season. The same plant can need water every four days in July and every three weeks in January. A fixed day of the week cannot account for any of that, so learn to ask the soil instead.

Three ways to tell

• The finger test. Push a finger into the soil up to the second knuckle, about two inches. If it feels damp, wait. If it feels dry, it is time for most plants. This is free and works well for small and medium pots.
• The weight test. Lift the pot just after watering, and again a few days later. A dry pot is noticeably lighter. After a few weeks you can tell at a glance, or at a lift, which plants need a drink.
• A meter. In large pots a finger cannot reach the roots. A soil moisture meter reads the soil down where the roots are and takes the guesswork out of big floor plants.

Know what your plant prefers

Houseplants fall roughly into three groups.

• Plants that like to dry out completely. Succulents, cacti and plants that store water in thick leaves or roots. Snake plants and ZZ plants belong here; in most homes they need water only every two to four weeks.
• Plants that like to dry out partly. Most leafy houseplants, including pothos, monstera and palms. Water when the top inch or two of soil is dry.
• Plants that like to stay lightly moist. Ferns, calatheas and many flowering plants. Water as soon as the surface begins to dry, and never let them dry right out.

How to water

When a plant does need water, give it plenty. Pour slowly over the whole surface of the soil until water runs out of the drainage hole. This wets the entire root ball, rather than just the top, and flushes out salts that build up from tap water and fertilizer. Then let the pot drain fully and empty the saucer after ten or fifteen minutes. A pot left standing in water soaks it straight back up.

If water runs straight through and out of the bottom, the soil has probably dried so far that it has shrunk from the sides of the pot. Stand the pot in a bowl of water for twenty minutes so it can soak up from below, then let it drain.

Drainage is not optional

Every pot needs a hole in the bottom. Without one, extra water has nowhere to go, and no amount of careful watering will stop it collecting at the base. If you love a decorative pot that has no hole, use it as a cover: keep the plant in a plastic nursery pot inside it, lift it out to water, and put it back once it has drained.

The pot changes everything

Pot material changes how fast the soil dries. A terracotta pot breathes through its walls and dries quickly, which is ideal for plants that like to dry out and a little harder work for moisture-lovers. Plastic and glazed ceramic hold water longer. A self-watering pot goes the other way, keeping the soil steadily moist from a reservoir below, and suits ferns and calatheas far better than succulents.

Size matters too. A small plant in a very large pot sits in a mass of soil its roots cannot reach, and that soil stays wet for a long time. Go up only one size when you repot.

Through the year

Plants grow most in spring and summer and slow down in autumn and winter, when the days are short. Slower growth means less water. Most houseplants need water half as often in winter, sometimes less. Central heating complicates this: it dries the air and the top of the soil, while the roots below may still be damp. Check deeper in winter before you water.

Reading the signs

• Too much water: yellowing lower leaves, soft or black stems at the base, soil that smells sour, tiny flies around the pot, and wilting even though the soil is wet.
• Too little water: crisp, brown leaf edges, leaves that curl or droop but recover within hours of a drink, and soil pulling away from the sides of the pot.

If a plant wilts, check the soil before doing anything. Wet soil and a wilting plant point to root trouble, and more water will make it worse. Let it dry out, and if it does not recover, tip it out of the pot to look at the roots. Healthy roots are firm and pale; rotten ones are brown, soft and come apart in your fingers.

When watering is not the problem

Sometimes a plant that needs water every day has simply outgrown its pot: there is more root than soil, and nothing left to hold moisture. If roots are growing out of the drainage hole, it is time to follow our repotting guide. For a busy household, a self-watering planter can also smooth out the gaps between waterings for the plants that suit it.