Start With the Compost, Not the Calendar

The single biggest mistake I see with houseplants in summer is watering to a schedule. A plant that needed a drink every five days in April might need one every second day in July — or, if it is sitting in a cool north-facing room, it might barely change at all. The compost knows. Your calendar does not.

Before you reach for the watering can, push a finger about 2cm into the compost. Not the surface — the surface lies. A crust of dry-looking bark or coir can sit on top of compost that is still properly damp underneath. If it feels cool and moist at fingertip depth, walk away and check again tomorrow.

For larger pots, or plants in gritty, free-draining mixes, a finger is not always enough. A cheap moisture meter pushed two-thirds of the way down gives you a far better picture, and a bamboo cane works well too: leave it in the pot for ten minutes, pull it out, and look for dark, damp patches along its length. If it comes out clean and dry, water. If it comes out streaked and cool, wait.

Water Thoroughly, Then Let It Drain

Little and often is the worst thing you can do to a houseplant. Sipping at the surface encourages shallow rooting, leaves the lower compost bone dry, and builds up salts from fertiliser right where the roots are trying to work. Aim for a proper soak instead.

Take the pot to the sink, or stand it in a bowl, and water slowly until it runs freely out of the drainage holes. Then let it sit for ten minutes or so and empty the saucer. That last step matters more than most people realise: standing water in a saucer wicks back up into the compost and slowly suffocates the roots. Roots need air as much as they need water, and permanently saturated compost is how you get root rot in the middle of a heatwave, which is a genuinely miserable thing to diagnose.

• Always empty saucers within half an hour of watering — no exceptions for decorative cachepots either.
• Use room-temperature water. Cold tap water straight from the mains can shock tropical roots, especially on tender plants like calatheas and marantas.
• Water in the morning where you can. Any splashes on foliage have time to dry before the cooler, stiller evening air arrives.
• Never let a plant sit in a full cachepot. If you cannot lift the inner pot out easily, tip the outer one over the sink.

Group Thirsty Plants to Build Humidity

Most of our houseplants come from humid forests, and a British summer indoors can be surprisingly dry — air conditioning, open windows and strong sun all strip moisture from the air. Grouping plants together creates a microclimate: as each leaf transpires, the neighbours around it benefit. It is a simple trick and it costs nothing.

Cluster your ferns, peace lilies, calatheas and other humidity lovers together in the same corner, keeping a little breathing room between pots so air can still move. If you want to push things further, stand the pots on a tray of pebbles with water kept below the level of the stones. The evaporation lifts humidity around the foliage without the compost ever sitting wet. Misting is fine as an occasional treat, but the effect fades within the hour — grouping and pebble trays do far more lasting good.

Keep in mind that grouping makes watering trickier, since the plants shade each other's compost. Check each pot individually rather than assuming the whole cluster is ready at once.

Match Your Approach to the Plant

Not every houseplant wants the same treatment in high summer. Getting this right prevents most of the casualties.

• Succulents and cacti are in their growing season, so they can take a good soak — but only once the compost has dried out completely, which may take two or three weeks even in July.
• Ferns, fittonias and calatheas want compost that stays lightly moist. Check them every couple of days in warm weather.
• Snake plants and ZZ plants are the exception to everything: they store water in their leaves and rhizomes and would rather be left alone. Once a fortnight is often plenty.
• Flowering plants such as orchids and African violets drink more while in bloom, but be careful never to wet the crown or leave water pooled in the leaves.
• Terracotta pots dry out roughly twice as fast as glazed or plastic ones, so factor that in.

Watch the Warning Signs

Plants tell you what they need long before they collapse. Yellowing lower leaves that feel soft and limp usually point to overwatering. Crisp, brown leaf edges and curled tips suggest the plant has been dry for too long. Drooping that recovers overnight after a drink is simply thirst; drooping that stays put is more likely to be root damage.

If you suspect a plant has been sitting wet, take it out of its pot, check the roots and trim anything dark, mushy or smelly with clean scissors. Repot into fresh, free-draining compost and hold off watering for a few days.

Holidays, Heatwaves and a Little Forgiveness

Going away for a fortnight in July is easier than you might think. Move plants out of direct sun, group them together in the coolest room, give everything a thorough soak the night before you leave, and stand them on a damp towel or a pebble tray. Most established houseplants will come through fine.

During a genuine heatwave, expect to water more often but resist the urge to compensate with extra volume. Give the same thorough soak, just more frequently, and keep an eye on anything sitting in a hot, glass-bright windowsill — those plants can dry out in a single day. A little shade moved across a south-facing window at midday works wonders.

Above all, be kind to yourself. Houseplants are forgiving, and almost everything recovers from a missed watering far more readily than it recovers from a fortnight of soggy roots. When in doubt, wait a day and feel the compost again.