Keeping Your Nerve
Hot, dry summers are becoming the rule rather than the exception, and the instinct in a heatwave is to panic and water everything in sight. Mostly, the better response is calm: water deeply, water what matters, and trust that established plants are tougher than they look.
The first thing to do in a heatwave is not to panic.
I know the urge. The borders wilt, the pots look desperate, and the temptation is to rush out with the hose and drench everything in sight, twice a day, in a kind of anxious penance. But hot-weather gardening is far more about judgement than effort — watering the right things, at the right time, in the right way, and having the nerve to leave the rest alone. Established plants are a good deal tougher than a hot afternoon makes them look.
And it’s worth learning this properly, because these summers aren’t a fluke any more. Long, dry, genuinely hot spells are becoming a fixed part of the British gardening year, and knowing how to garden through one calmly is fast becoming an essential skill rather than an occasional one.
When to water
Water in the early morning or the evening, and avoid the middle of the day. That’s the whole of it, really.
The reason is simpler than the one you’ve probably been told. In the heat of the day, so much water evaporates before it ever soaks in that you’re half watering the air — a waste of water and effort both. Do it in the cool of early morning or at dusk and far more reaches the roots, where it’s actually wanted. Of the two, I’d lean towards morning if you can: the plant goes into the heat of the day properly hydrated, and the surface dries before nightfall, which the slugs appreciate less than you might think.
While we’re here, let me lay one old myth to rest. You may have heard that watering in sunshine scorches leaves, because the droplets act as little magnifying glasses and burn the tissue beneath. For almost every plant you grow, this simply isn’t true — it was tested properly, and water sitting on smooth leaves like maple or ginkgo caused no damage at all. The effect only occurs on certain hairy-leaved plants, where the hairs hold the droplet up off the surface. So don’t fret about the odd splash on the foliage. The reason to avoid midday watering is waste, not scorch.
Where to water
Aim for the base of the plant, not the leaves. The roots are where water does its work, so that’s where to direct it — watering the foliage mostly just feeds evaporation.
If you’ve plants packed close together and can’t help wetting a few leaves, don’t worry about it. As long as you’re not doing it in the midday heat, the water runs off and finds its way down to the soil soon enough.
Water deeply, not often
Here’s the technique that matters most, and the one the quick guides tend to skip: a good long soak now and then beats a daily sprinkle every time.
A light splash every day only wets the surface, which evaporates almost at once and coaxes roots up towards the top of the soil where they’re most exposed. A proper drenching, less often, sinks down deep and draws the roots down after it, to where the soil stays cool and damp long after the surface has baked dry. Deep roots are what carry a plant through a drought. So water thoroughly, let the top of the soil dry out between times, and resist the fussy daily dribble.
Pots are the exception
Containers are the one place you do need to be vigilant, and often twice a day. A pot holds only a small volume of compost, and it dries out far faster than open ground — a hot, breezy day can empty one by teatime. On the worst days, plan to water pots in the morning and again in the evening. Grouping them together helps: huddled up, they shade one another’s sides and hold a little humidity between them, so they don’t dry quite so fast. And any pot you can move into afternoon shade will thank you for it.
Some plants need rescuing; most don’t
The great skill of a heatwave is triage — deciding what genuinely needs help and what’s fine left alone.
The vulnerable ones go first. Anything in a pot. Anything you planted in the last year or two, still finding its feet. Seedlings and young plants. Vegetables in full growth. And a few plants scorch more than others — acers, the Japanese maples, are notorious for it, their delicate leaves crisping at the edges in hot sun and drying wind. If yours are in pots, move them somewhere shadier; if they’re in the ground, they’ll usually recover once the spell breaks.
Almost everything else you can trust. Established shrubs and perennials are far deeper-rooted and more resilient than a wilting midday appearance suggests — many droop in the heat simply to cut their losses, and perk up again by evening without a drop of help. And the lawn? Let it go brown. It looks alarming, and it is completely fine; grass is built for this, and turns green again within days of the first proper rain. Pouring precious water onto a lawn in a drought — often when there’s a hosepipe ban on anyway — is about the least useful thing you can do with it.
Don’t start anything new
Finally, the easiest advice of all: don’t sow seed or plant anything new in the thick of a heatwave.
A new seedling or a freshly planted shrub has no established roots to fall back on, and baking heat is the hardest possible start. Hold off. Wait for the weather to break and the soil to cool, then get stuck in — everything you plant will establish faster and easier for the patience.
Which is rather the theme of the whole business. A heatwave asks less of you than it seems to: water deeply and early, look after the pots and the newcomers, and trust the rest of the garden to look after itself. It has done this before. It knows what to do.
(For the longer game — building a garden that shrugs off dry summers in the first place, with mulch, water butts and plants that actually want the heat — see The Case for Doing Less.)