Watering Container Plants Through Dry Spells

Why Pots Give Up Their Water So Quickly

A container is a small, exposed world. There is only a shallow body of compost to hold moisture, roots cannot travel in search of more, and the pot itself sits in the sun with wind moving across it all day. Terracotta loses water straight through its walls, and a dark plastic pot in full afternoon sun can get hot enough to cook the fine roots near the edge. A plant in the open border may need watering once a week; the same plant in a pot can need it twice a day in July.

You will spot trouble before the leaves flag if you learn to read the compost. Pull the pot's weight in your hand, or push a finger in to the second knuckle. If the compost has shrunk away from the sides of the pot, leaving a visible gap, you are already behind. So if water runs down that gap and straight out of the bottom, the root ball is still bone dry.

Check Twice a Day, Every Day

During dry spells, make two rounds: one in the morning, one in the evening. The morning check tells you what needs topping up before the heat arrives. The evening check tells you whether the day has taken more than you expected, and gives you a chance to rescue anything that has suffered.

Water in the morning when you can. Plants then have the whole day to drink and to dry their foliage, which keeps fungal problems and slugs at bay. An evening soak is perfectly good too, especially for a pot that has dried out badly through a hot afternoon, because it will recover quietly overnight. What you should avoid is a quick splash at midday, when much of it evaporates before it reaches the roots.

• Check hanging baskets first. They dry fastest of all and can be parched by teatime.
• Push a finger into the compost rather than trusting the surface, which dries misleadingly fast.
• Lift the pot. A well-watered pot is noticeably heavy; a dry one feels alarmingly light.
• Check again after wind, not just after sun. A breezy day dries pots as hard as a hot one.

Water Deeply, Until It Runs Free

Little and often is the classic container mistake. A daily splash wets only the top few centimetres, encourages shallow rooting, and leaves the lower compost permanently dry. Instead, soak each pot until water runs freely from the drainage holes, wait a few minutes, then go round again. Two or three passes let the compost re-wet properly rather than shedding the water.

If a pot has gone truly dry, the compost can become water-repellent and refuses to absorb anything. Stand the pot in a bucket or trug of water up to its rim and leave it for half an hour, or until the surface feels damp and the pot is heavy again. A wetting agent stirred into the can helps stubborn compost take water up more evenly for the rest of the season. Where compost has shrunk from the sides, firm it back gently and top-dress with fresh material so water soaks in rather than running away.

Group Pots Together to Beat Evaporation

Scattering pots across a patio is the quickest way to lose water. Grouped together, they create their own microclimate: shared shade, higher humidity around the leaves, and far less wind reaching each pot's surface. Arrange the thirstiest containers in the middle of the cluster and the drought-tolerant ones, such as rosemary, lavender and thyme, on the sunny outer edge.

During the hottest afternoons, shift the whole group into dappled shade. Even moving pots from full sun to the shade of a wall for the worst fortnight of the summer saves a surprising amount of watering. A mulch of two or three centimetres of gravel, bark or shells on the compost surface slows evaporation and keeps the root zone cooler. For a neat trick, double-pot: sink a plain plastic pot inside a larger decorative one, packing damp sand or newspaper between the two.

Make the Compost and Pots Work Harder

• Choose larger pots where you can. A bigger volume of compost dries out more slowly than a small one, and gives roots room to keep cool.
• Keep thirsty plants in glazed or plastic containers, and save porous terracotta for drought-tolerant subjects.
• Mix in well-rotted compost or a modest amount of water-retaining granules at planting time to hold moisture in the root zone.
• Use saucers and trays to catch runoff so it can be drawn back up, but empty them if a plant is prone to rot, and never leave pots standing in water for days.
• Consider a self-watering container with a reservoir for tomatoes, courgettes and anything else that sulks when it dries.

Reading the Signs in a Heatwave

Wilting at midday with damp compost is normal: the plant is closing its pores to conserve water and will perk up by evening. Wilting at dawn is a genuine cry for help. Yellowing lower leaves, soggy compost, green algae on the surface and clouds of fungus gnats all point the other way, to overwatering, so ease off and let the top few centimetres dry.

In a prolonged heatwave, water morning and evening, move pots into shade, and pause the feeding, because strong feeds in dry compost can scorch roots. Feed only into moist compost. Rainwater stored in a butt is ideal, though tap water is fine for most plants; leaving a full can to stand overnight takes the chill off it. A few minutes twice a day is the price of a container garden, and honestly, it is often the best part of the day.