A heatwave doesn't really test your plants. It tests your soil. Here in the UK, a heatwave often can feel like it’s sprung out of nowhere, leaving you feeling unprepared. This guide will help you to understand the methods you can use in the long term to build a resilient garden, and act quickly when unexpected heat arrives.
When the temperature climbs and the rain stops, what stands between a thriving border and a row of collapsed seedlings is rarely how often you reach for the watering can. It's what's happening underground; how much moisture the soil can hold, how deep the roots run, and how resilient plants are to stress.
That's worth understanding before the next hot spell arrives, because most heatwave gardening advice treats the symptom. Wilting leaves, scorched edges and dry pots are signals, not the problem itself. The gardeners whose plots sail through a heatwave with little to no effort are usually the ones who did the work weeks, months and even years earlier, in the soil.
This is a guide to all three stages: building resilience before the heat, watering well once it hits, and bringing plants back after a particularly warm spell.
Resilience: How to grow plants that can deal with the heat
A plant's ability to cope with heat is largely down to what’s happening beneath the soil. When your focus is on improving your soil, the work pays off a little more each year.
Build soil that retains moisture
The single biggest factor in how your garden handles drought is how much water your soil can store. If your soil is bare, compacted or sandy, water may run right through, or simply sit on the surface, never soaking in. Soil rich in organic matter behaves like a sponge by capturing moisture and releasing it slowly to the roots over days. The first season you work on improving your soil naturally you’ll notice the difference, but it’s the years that follow where you’ll really see the impact that it can have as nature does its thing.
Working organic matter such as compost, frass and biochar into your beds changes the physical and biological nature of the soil. Biochar's porous structure gives water somewhere to sit; research from the USDA has shown treated soils holding 25–40% more moisture at the root zone than untreated ground. Insect frass and well-rotted compost feed the soil life that builds this water-holding structure over time. None of this is a quick fix you apply mid-heatwave, it's a foundation you lay in autumn and spring that pays off all year long and something worth considering as you’re potting on and planting out.
Train roots to dig deeper
Plants watered little and often grow lazy, shallow roots that sit near the surface where the soil dries first. Plants watered deeply and less frequently send roots down in search of moisture, and those deeper roots are what keep them standing when the top few centimetres turn to dust.
This isn’t just a lesson for time around a heatwave, learning to water your plants properly, it is a life lesson that will help you to grow stronger, more resilient plants all year round. Water thoroughly, let the soil on the first few cm at the top of the soil are completely dry before you water again. Below you’ll find an in-depth guide on how to water your plants, properly.
Prime plants to handle stress
Some of a plant's resilience is biochemical. Under heat and drought, plants produce their own protective compounds: proline, antioxidants, and betaines. These help them hold water and limit damage. A seaweed feed, applied in the days before heat arrives, has been shown to raise these stress-protective compounds and improve a plant's water-use efficiency. In trials, plants treated with seaweed extract held more water in their leaves and recovered faster than untreated ones.
The honest framing here: cold-pressed seaweed isn't a fertiliser you pour on to force growth. It's a biostimulant that helps a plant become a better version of itself before it's put under pressure. A good, deep water and a seaweed feed in the day or two before a forecast heatwave is one of the most useful things you can do. Just make sure you know the difference between cold pressed seaweed feed that benefits your plants in the long-term and alkaline seaweed feeds that are short-term, quick greening products.
If you're planning or replanting, it's also worth leaning on plants that are simply built for dry heat, plants such as lavender, rosemary, sedum, ornamental grasses and other Mediterranean species with silvery, waxy or hairy leaves. Once established, they ask very little of you in a drought.
Watering: How to water plants in a heatwave
When the heatwave lands, the goal shifts from building resilience to protecting what you have. Watering well is mostly about timing, technique and restraint.
Water early, or water late. The best time to water is early morning, before the heat of the day, so moisture soaks down to the roots before it can evaporate. This is the best way to reduce the risk of your plants wilting in the heat. If you miss the morning slot, or didn’t water thoroughly enough, the evening, after the sun has dropped, works too. Watering at midday wastes most of what you pour out to evaporation and does little for the roots. You also risk leaves being scorched by water droplets left sitting on the leaves.
Water deeply, not often. A proper soak every few days does far more good than a daily sprinkle that only wets the surface. You're aiming to recharge the soil at root depth, not dampen the top. Push a finger in around 2-3cm, if it's dry below the surface, water; if it's still damp, wait.
Water the soil, not the leaves. Aim at the base of the plant. Water sitting on foliage in strong sun mostly evaporates, and damp leaves overnight can invite fungal problems.
A few techniques are especially worth knowing in real heat:
Bottom watering for pots and trays. Put trays and pots into a gravel tray or trug half-filled with water. This encourages plants to draw moisture up through the base, delivering water straight to the roots with almost no loss.
Olla pots and drip feeders for pots and borders. Olla pots (a porous type of terracotta pot) releases water slowly underground, exactly where it's needed. You can also use old plastic bottles with holes poked in as an alternative drip feeder.
A layer of mulch for pots and borders. Materials such as bark, straw and compost work well when laid over the soil. This can dramatically slow evaporation and keep roots cool. It's the simplest, cheapest way to make every watering can go further.
A classic watering can for anything in the garden. When you’re watering with a traditional can, the biggest things to remember are to pour slowly, allowing the soil to soak up the moisture, and the only water the soil, not the leaves.
Containers, hanging baskets and grow bags need the closest attention. They have no soil reserve to fall back on and may need watering daily, sometimes twice. Tomatoes in grow bags can drink two to three litres a day in rising temperatures. Where you can, it’s worth moving pots and baskets into afternoon shade until the heat passes, as moving them is far easier than nursing them back.
If a hosepipe ban is in force, this is where good soil pays you back. Hand-watering with collected rainwater, generous mulch and moisture-retentive soil can carry a garden through restrictions that would flatten a thirsty, bare-soiled plot. Prioritise anything planted in the last 12–18 months and crops near harvest; established, drought-tolerant plants can usually look after themselves.
Recovery: How to revive wilting plants
Even a well-prepared garden can take a hit in extreme heat, particularly here in the UK where temperatures can rise and fall in very quick succession. The instinct is to rush in and rescue, but the most effective recovery is patient and gentle.
Give it shade and time. You can create temporary shade with a sheet of fleece, a parasol, a length of netting or anything that can work to take the pressure off while a plant recovers. Then be patient. For perennials, as long as the crown hasn’t been damaged they’ll typically come back in time. If your annuals aren’t completely dry and crispy, there’s a chance that they too will recover.
Don't strip off the scorched leaves. Sunburnt foliage looks dreadful, but it's shading and protecting the rest of the plant. Resist hard pruning while the heat lasts, as this can cause plants further stress. The plant will naturally shed the leaves it doesn’t need, or you can snip them off yourself once the heat has passed. You can, however, continue to deadhead any spent flowers.
Water deeply and slowly, in the evening. A plant in genuine heat stress can't take up water fast, and a midday flood mostly runs off or evaporates. Wait for the sun to drop, then water slowly and thoroughly at the base so it has the cool of the night to rehydrate. Check your plants again in the morning to see if they need more water for the day ahead.
Hold off on heavy feeding. A nitrogen-rich alkaline seaweed fertiliser mid-heatwave pushes a stressed plant to make tender new growth it can't support. What helps instead is a gentle biostimulant. A diluted cold-pressed seaweed feed supports root recovery and helps a plant rebuild its own stress defences without forcing growth.
How to care for your lawn in a heat wave
Of everything in the garden, the lawn is the thing worth worrying about least, yet it's where people waste the most water.
A lawn that turns brown in a heatwave isn't dying. It's doing exactly what grass evolved to do: going dormant to protect itself: shutting down top growth and retreating to the roots until rain returns. Left alone, an established lawn greens up again within a week or two of a good soaking. Pouring precious water, or running a sprinkler through a hosepipe ban onto grass that's simply resting is effort the rest of your garden would put to far better use.
If you can make your peace with a brown lawn for a fortnight, the kindest thing you can do is mostly nothing. A few principles help:
Stop mowing, or raise the blades right up. In real heat, leave the mower in the shed as cutting stresses grass that's already struggling lowers its chances of recovery. When you do mow, set the height high (around 6–8cm); longer blades shade the soil and slow moisture loss.
Don't feed. A high-nitrogen lawn feed in a heatwave can scorch the grass, drawing water out of the plant rather than into it. Wait until growth resumes.
Leave the clippings. Your grass clippings can act as a shade for the soil’s surface and returns moisture and nutrients as it breaks down.
Keep off it where you can. Grass under heat stress bruises easily underfoot and is slow to recover from the wear.
If you do need to water, particularly if you’ve got a young or newly-laid lawn that hasn't yet rooted deeply, water it as you would anything else: one deep soak early in the morning, not a daily sprinkle. And when the heat finally breaks, a diluted seaweed feed or a natural lawn feed helps a tired lawn rebuild its roots and colour faster than it would alone.
For a truly resilient garden, the work starts long before a heatwave. But, instead of panicking as temperatures rise, follow these easy, actionable steps to protect your plants and ensure they thrive through the heat and produce the greenery and harvests you’d hoped for. Take a look at our range of natural soil improvers to build a drought-resistant garden and handle whatever the British weather throws your way.
