Our gardens are suffering from heatwaves more regularly as climate change becomes harder to ignore. Even in the cold north, drought and baking sun put huge strains on our once lush lawns and native plants.
Without reverting to completely new styles of planting, knowing how to protect your garden from a heat wave means saving water, clever planting, and, above all else, getting to know your plants.
How heatwaves affect your garden
It’s all well and good telling gardeners to plan ahead, but when your current planting is struggling from dry soils and wilting foliage, it opens plants up to problems:
- Fungal problems from high humidity
- Weeds set seed faster in high temperatures
- Grass becomes patchy and dry
- Annual plants and vegetables have shorter seasons, and set seeds too quickly
- Vegetables can split their skins on the plant
- Hose pipe bans limit our water use
- Sunburn can kill young or tender plants
- Wildlife stops visiting due to dried ponds and bird baths
- Pollinators stay in the shade to sustain energy
Despite our garden still struggling with Zone 7 winters, summers now seem to go through three or even four heatwaves that are reminiscent of Zone 9 or 10. That means our plants need to be able to cope with extremes at both ends of the spectrum.
Colder winters mean choosing hardier plants or protecting them with fleece. Hotter summers mean collecting water and choosing plants that can cope with drought. It’s a fine balance and requires planning ahead. So, how do you protect a garden in a heatwave right now?
Ways to protect plants from a heat wave
There are dozens of ways to prepare your garden for a predicted heatwave, and plenty of methods that can help you to revive plants after a heatwave too. But before we get into it, it’s important to say that the most important advice is also the simplest:
- Water directly, and sensibly
- Water in the morning
- Collect any rainwater, and consider grey water
- Move pots into shade
- Mulch plants to conserve water and protect soil
- Provide water for wildlife
- Don’t cut your lawn
How to water your garden in a heatwave
Watering is key to projecting a garden during a heatwave, but it’s also important to be conservative. Remember, you’re not the only gardener in this situation, and overusing mains water during a heatwave is wasteful, and irresponsible, so follow our heat wave watering guide below to prepare your garden in advance and make the most of limited water.
Avoid spray irrigation or sprinklers in heatwaves
Sprinklers and spray irrigation systems (including misters) are an absolute no in heatwaves. Not only are they a wasteful way to water your garden, but they can also harm plants, promote fungal and bacterial problems, and encourage pests.
Spray irrigation is bad for plants in a heatwave. It promotes sunburn and mildew.
Sprinklers are also wasteful. Around 35% of the water you use simply evaporates, either before it hits the ground, or from foliage. Watering directly at the roots reduces evaporation down to around 2% even in dry heat.
Use water butts, not hoses
Water butts should be installed in every garden. They bring bills down and reduce reliance on mains water by collecting rain from downpipes and rooves. Not only is it cheaper, but rainwater is actively better for your plants than tap water, which prefer the gently acidic, chemical-free softness of collected water.
Grey water, the by-product of dishwashing, clothes washing, showers, and baths (basically everything that leaves your house other than the toilet) is a great resource for the garden. While grey water shouldn’t be used as a permanent resource, 99% of garden plants can cope with soapy or slightly direct water for short periods.
For anyone doubting grey water, we experimented with a section of the garden this year, including tomatoes, courgettes, and sweet peas. All have cropped successfully and produced beautiful displays of scented flowers.
When to water in a heatwave
Watering in the morning is better than water in the evening, as plants can drink during their active hours. Other than Night Scented Stock, Nicotiana, and a few Jasminum species, most plants do their work during the day. Watering in the evening means plants aren’t actively seeking moisture, and water can drain before they start drinking.
Most gardeners agree that watering in the afternoon is a bad idea during a heatwave. Water is used up faster by plants, and is more likely to evaporate, or spread into dry soil. Instead, water in the morning or evening when the sun is lower and plants have a few hours to take in moisture.
Water slowly to waste less
As well as where to water, and when to water, how you water matters in a heat wave, particularly for pot plants. Water plants slowly, stopping to allow water to soak into the soil. Watering plants quickly can mean that water simply drains down and out of the container.
Target water on young plants
If your area has a hosepipe ban in place, target your water on the plants that need it most. Most hardy plants and perennials might suffer through the heatwave but will recover afterward. Seedlings, young trees, or recently planted shrubs will need watering deeply at least twice a week in a heatwave, if not every day.
Leave buckets of water around the garden to provide humidity
If you’re going to be away for a week or more, and there’s any risk of a heat wave, fill buckets with water and dot them around the garden. As the sun warms them up, they slowly evaporate, creating humidity around pots and ornamental shrubs.
We swear by this tip, not just in heat waves, but when we go on holiday too. Avoid this technique around annual plants and vegetables, where humid heat is much worse than dry heat.
How to provide garden shade in a heatwave
There are plenty of ways to provide shade in the garden, from pergolas to plants, and plenty of instant fixes to give your garden some respite from a heatwave. The three best ways to provide shade in a heatwave are:
- Companion planting
- Root shade
- Row covers
Shading roots, otherwise known as mulching, is often done in winter to protect tender perennials from frost, but is equally useful in summer to protect the soil from the baking sun, and prevent evaporation. We’ll cover mulch in more detail later.
Row covers are a great way to protect plants from a heatwave. Using garden fleece to shade delicate seedlings and rows of vegetables can slow down bolting, and keep alliums and herbs in their vegetative stage, rather than setting fruit or seed too early in the season.
Companion planting is a clever way to prepare for heatwaves in the future, but choose tall tuberous plants which won’t take too much from the soil, or compete for water. Tuberous and rhizomatous plants have fleshy roots which can store water in reserve. During a heatwave, they call on those reserves, while fibrous-rooted plants take up most of the water.
Great companion plants for heatwaves include Jerusalem artichokes (which grow like sunflowers and can be harvested as a food crop too) and iris, which prefer damp conditions but can cope with drought too.
Greenhouse protection in a heatwave
Greenhouses need a lot of care during a heatwave as temperatures can easily exceed 110°F. Even tropical crops like tomatoes will struggle in through conditions, so ventilation and shade are a must.
If you have a large enough tarpaulin, cover the top of the greenhouse to reduce light, or use white, washable glass paint to create a reflective surface that allows light through, but reduces heat. Traditionally, greenhouses were shaded using slaked lime, a mixture of calcium hydroxide powder and water, which created a cheap translucent mixture that was thrown onto greenhouses and washed off by rain.
Ventilation is key too. If you know there’s a heatwave around the corner, open all the windows, doors, and vents of your greenhouse to provide through flow, so the temperature stays roughly similar to the outdoor heat. Otherwise, your plants can burn and wilt.
Mulching & soil care in a heatwave
There are so many ways to shade plant roots during a heatwave but pretty much everything will work. Mulching is a method of protecting plant roots and soil from frost and high temperatures. The most common mulch is compost, but any of the below work equally well for a quick fix:
- Grass clippings
Leave the soil alone
Disturbed soil loses moisture faster, so don’t weed during a heatwave, other than to remove seed heads and flowers. By opening up soil structure, water can evaporate faster from deeper down. Undisturbed soil allows worms and soil bacteria to continue thriving beneath the surface.
Caring for container plants in a heatwave
Container plants, or pot plants, are always the worst affected by a heatwave, but there are a few ways to protect them from high temperatures:
- Change terracotta pots, or coat them
- Group pots together
- Move pots to shade
- Leave pots standing in shallow water
Terracotta pots lose water through their well as well as the drainage holes at their base. Use plastic or glazed ceramic pots instead, as moisture remains in place regardless of temperature. Alternatively, use a clay pot sealer to seal porous ceramics.
Due to improved drainage, and having no access to groundwater, containers will need watering daily during a heatwave. With a little bit of foresight though, this can be reduced to every other day or just twice a week.
Start by moving your container plants into the shade, which will dramatically improve their survival during a heatwave. As well as finding shade, group pots together. This increases humidity, and their soil will dry out much slower.
Finally, use a large drip tray to group multiple pots together. Fill the tray with water and stand pots in it. They will drink from their base and the added humidity can mean they only need watering twice a week, even in the hottest heat.
Caring for wildlife in a heatwave
Gardens aren’t just about plants. They are habitats, and wildlife havens too. The symbiotic relationship between insects, birds, mammals, and your garden flora needs support through heatwaves. But don’t worry. It’s really quite easy:
- Mulch soil to protect worms and soil life
- Fill birdbaths daily
- Top up and shade ponds
- Provide seeds and fruit for birds and small mammals
- Turn off water pumps
Mulching isn’t just good for plants, it’s a great way to preserve the soil life, worms, and bacteria through a heatwave, so they can help resurrect soil health when the rain returns.
Keep ponds and birdbaths filled, and provide shade to reduce evaporation and save water. Simply lay a few planks across a pond, and place bricks in so bathing wildlife can crawl out safely. Birds need seeds to maintain their energy, so making seeds readily available is useful, but so is fruit (berries or apple slices) which have higher water content,
And last, but not least, turn off your water pumps. Ponds with fountains or moving water will lose water faster, and pumps can be damaged by low water levels.
How to maintain your garden in a heatwave
Plants that need extra care in a heatwave
On top of the general advice for protecting your garden in a heatwave, it’s important to know where to adapt and change, to protect the most sensitive or precious plants in the garden.
- Fruit & Veg
- Herbaceous plants
Fruit & Veg like tomatoes, peppers, cucumbers, courgettes, and sweetcorn are obviously sensitive to drought, but keep alliums like leeks and onions wet too. Also, water soft herbs and any biennial vegetables regularly to prevent them from bolting and setting seed before the leaves, stems or bulbs ripen.
Some herbaceous plants like gladioli and Japanese anemones can really struggle with drought. Consider covering them with individual tarpaulins. A few days in the dark is better than fried foliage, and they will jump back into life in a couple of weeks.
When it comes to lawn care in a heatwave, just forget about it. If you’ve got a hosepipe ban, or your area has been affected by drought, a few weeks of brown dusty lawn isn’t the end of the world. Let your lawn grow out a little, and definitely don’t cut it any shorter than 3”. If you do water your lawn, water evenly in the morning with a hose rather than a sprinkler system, and target dry patches.
The last and most important plant group to keep an eye on during a heatwave is weeds. Ornamental annuals and weeds both seed around the garden in the same way, usually at the end of summer. Heatwaves speed up that process and will force plants to flower earlier, and produce seeds as a survival mechanism. Deadhead weeds and annuals regularly to prevent spread.
Pruning in a heatwave
Don’t prune during a heatwave. Even roses, jasmine, and wisteria, which are time-sensitive pruners, should be left and cut a little later. New shoots can wither in the high temperatures meaning no flowers next year. Instead, just remove dead, damaged, or diseased growth to keep plants healthy.
Keep planting through heatwaves
Don’t let the heatwave change your schedule. Heatwaves are called waves for a reason, they pass. If your planting calendar says to plant seedlings out, then do it, but provide row covers and mulches, and water them in really well.
Plant in the evening so plants can acclimatize gradually to extreme temperatures in the morning, and not face a sudden shock in the afternoon.
How to feed plants in a heatwave
It’s important to water dry soil before feeding. Dry soil, even with diluted plant food, can burn plants that scramble to drink up the water, instead of gradually taking in nutrients. Only feed wet soil to avoid burning plants with undiluted feed.
Caring for your garden in a heatwave is a challenge. There are no shortcuts, and no easy hacks for heatwave gardening, so you’ve got two choices: Protect your garden or plan ahead. Choosing drought-tolerant plants that can cope with both freezing and heat waves is going to be an essential part of gardening here in the future, but that doesn’t mean you should give up on traditional garden favorites.
Collect water, and use whatever you can. Water sensibly, and protect tender or young plants from the worst of the heat while grouping pots and containers together. Just do what you can, and when the heatwave is over, you’ll be rewarded with a surprising display of resilient flowers and fruit breathing a breath of cool air after the heatwave.