After the two hottest May days on record in the UK last month, gardeners may be surveying the damage and dreading the summer months ahead. “Heatwaves early in the summer can result in scorched, brown leaves,” says Leigh Hunt, the principal horticultural adviser at the Royal Horticultural Society. “When temperatures climb over 35C, there are more extreme effects.” (Thermometers hit 35.1C in London on 26 May.)

But don’t put down your trowel in defeat just yet. “Plants were caught out by the sudden change in temperature,” says Hunt. “They are a bit more naturally resistant later in the summer.” Plus, there is plenty you can do to support them without wasting gallons of water or installing an inefficient sprinkler system – and the payoff is massive. “Plants provide shade and release moisture; they cool our towns and cities by 2C to 4C,” says Hunt. “Your little bit of greenery is part of a network of greenery doing its bit. It makes the places we live better and cooler.”

So, whether you have a few pots or a Wimbledon-worthy lawn, here’s how to help your garden thrive in a heatwave.

When should I water?

British Garden Centres, a family-run company with 80 garden centres across England and Wales, has a useful watering guide for novices. In hot weather, it recommends watering in the early morning, when the soil is cooler and the water will soak in rather than evaporate. If you don’t have time first thing, late evening works well, too.

How should I water?

If you can, use a watering can rather than a hose. “It gives people more of a feel for how much water is required and how much they’re using,” says Hunt. According to British Garden Centres, this can make a big difference, with a hose using roughly five times as much water as a watering can for the same result. Hunt acknowledges that a hose may be more practical for some people, though, such as those who would struggle to carry a heavy watering can.

Either way, fit a sprinkler attachment. “This makes it more like natural rain,” says Hunt. “If you jet it on, it tends to run off.” Direct the water under the foliage to the compost or soil at the base of the plant. “If a plant is struggling, shape the soil around it like a dish to direct the water to the rootball.”

And how often?

That depends on your garden. Hunt says: “Lawns don’t need watering. A lot of established plants in the ground don’t need watering, either, and once a week might be enough for others.” Pots, however, may need daily watering.

Jason Williams, AKA the Cloud Gardener, grows pots on the 18th-floor balcony of his flat in Manchester. He says containers can dry out extremely quickly in the heat. “To check if your plant is thirsty, put two fingers into the soil and go up to your knuckle. If the soil is dry all the way down, your plant needs a drink.”

Avoid a quick daily splash, though. Julian Palphramand, the head of plants at British Garden Centres, says: “The biggest mistake people make in warm temperatures is watering little and often. All it does is keep moisture near the surface; roots stay shallow and the plant becomes more dependent on you. Give them a good, deep soak less frequently and they’ll push their roots down to find water themselves.”

Try not to think of it as a chore, says Williams: “Watering your plants is a lovely moment of mindfulness – good for your plants and good for you.”

Should I use tap water?

“Rain comes free from the sky!” says Hunt. “If you have access to a drainpipe and a roof – either the house or the shed – you can buy an inexpensive rainwater diverter kit.” If not, simply collect rainwater in a butt or a similar container. “The intensity of rainfall in the summer months can be quite heavy. After a summer downpour, you could have 50 litres of water,” Hunt says. The RHS is encouraging people to make a pledge to switch from “Mains 2 Rains”.

Don’t forget grey water, too. “Collect what you can from the house,” says Hunt. “The best-quality grey water is from washing vegetables. Bathwater, or a bucket in the shower, is fine, but might contain small amounts of bacteria. Just use it for ornamental [not edible] plants.” Williams suggests leftover pasta cooking water or dishwater, if not too dirty or full of harsh detergents.

But don’t leave grey water sitting in a bucket for days, says British Garden Centres – use it within 24 hours.

How else can I save water?

Hunt suggests putting saucers under smaller pots to catch any runoff from watering. Williams goes further – he sits plants in large, shallow water containers such as trays, bowls or plastic food packaging and waters into those. “This enables the roots to take up water from below. Water will evaporate into the plants’ leaf zone and slightly cool the air around them,” he says. Be careful not to overwater, though – you don’t want your plants sitting in water for long.

What sort of compost should I use?

British Garden Centres advises using a moisture-retaining compost, as this will help establish a healthy root system, which allows plants to cope with dry conditions without needing constant attention. Hunt suggests using compost rich in bulky organic matter, such as that labelled “farmyard manure”. Avoid fine potting compost, which doesn’t retain water well.

Do I need to add plant food?

Mark Sage, the lead horticultural buyer at B&Q, says: “With the extra watering heatwaves often bring, it’s also important to keep feeding flowers, fruit and vegetables, particularly those in containers, as regular watering can wash nutrients out of the compost and leave plants less resilient.”

However, as Hunt points out, feeds have a carbon footprint. He suggests using a more sustainable seaweed-based liquid feed, or making your own from plants such as nettle or comfrey.

Is it important to mulch?

Yes – especially for containers. British Garden Centres says a layer of bark or compost mulch around the base of your plants keeps moisture in the soil for longer, keeps the soil temperature down and means you can water less often. It says gravel also works well in sunny spots to stop water running off the surface before it has a chance to sink in.

Again, though, you don’t need to spend money on mulch. Hunt advises using the waste products from your garden, such as homemade compost or leaf mould. “Any organic matter acts as a sponge,” he says.

What else can I do to protect my pots?

Williams, who is a judge for the National Trust’s Sky Gardening Challenge for people who live in flats, has lots of tips. First, use the biggest pots you can, as they will hold moisture for longer; shallow trays and small pots dry out fastest. Second, group plants together to create a microclimate, which may slow transpiration (the rate at which they lose water vapour through foliage) and makes them easier to water. Third, create more shade through screening with spare sheets, old towels, fabric or used compost bags; move your plants to shadier spots if they are not thriving.

Finally, he says, accept that there may be casualties – balconies in particular are challenging places to grow. “If my plants have flopped, I set them to one side of my balcony called the ‘Struggle Bus’”, he says. “It’s a shaded corner of the garden and is my own plant nursery, where they get special care and can revive at their own pace.”

What should I plant?

“What did well even 10 years ago is not doing so well in summer months now,” says Hunt. “Plants need to be more heat-tolerant, but also more wet-soil winter-tolerant.”

Many experts recommend Mediterranean-style plants. British Garden Centres says lavender, rosemary, thyme, sage and oregano need little water once they’re established and are good for pollinators. The same goes for ornamental grasses: sedum, verbena, eryngium, euphorbia, hebes, osteospermum and achillea.

The RHS has a list of drought-resistant specimens, from flowers for hanging baskets to shrubs and trees. Hunt recommends having a nosy at what is thriving in your neighbours’ gardens, as well as visiting formal gardens for inspiration. RHS Hyde Hall in Essex, for example, has a “dry garden” with 400 species of plants from the Mediterranean, South Africa, South America, Australia and California. He says it is worth splashing out on perennials rather than annuals: “Perennials cost a bit more money initially, but will last many years, storing carbon.”

Before planting, says Sage, “give them a thorough soak by standing them in a bucket of shallow water for around an hour, so the rootball is fully saturated”.

How can I keep my lawn alive?

Everyone advises raising the cutting height on your lawn mower. Longer grass develops deeper roots and handles heatwaves much better than closely cropped turf; it will shade the soil and reduce moisture loss. In practical terms, Hunt adds: “A longer lawn will be more resilient if the kids are home for the summer playing football on it.”

Sage says: “It’s also worth remembering that a brown lawn isn’t necessarily a dead one. During long dry spells, grass often goes dormant. It will usually recover once cooler, wetter weather returns.”

If you have bare patches that need reseeding, look for a mix with a higher proportion of fescue. British Garden Centres says it is more drought-tolerant than most standard lawn seed.

Are ponds a waste of water?

Not at all. “Ponds are the top things you can add for wildlife,” says Hunt. Try to top them up with stored rainwater, as tap water encourages algae. If you’re out of rainwater and the pond is really low, use tap water that you’ve stored in a bucket overnight. A lack of space is not an excuse. “I have ponds on my balcony,” says Williams. “Having a water source attracts pollinators and creates an ecosystem. Plus, I can fertilise my plants with the water from the pond.”

What about houseplants?

“Don’t forget indoor plants during a heatwave,” says Sage. “Move any sitting in strong direct sunlight to a shadier spot. Where practical, many houseplants benefit from spending the summer outdoors before coming back inside in autumn.”

How can I heat-proof my patio?

“Keep hard surfaces to a minimum – they store heat in the day and give it off at night,” says Hunt. “Grow climbers around the patio area, which will have a cooling effect.”

And enjoy it, he says. “The nicest thing on a hot day is sitting under the shade of a tree, enjoying a cup of tea or a glass of wine. If you have a small tree or a large shrub, cut the lower branches and sit under a living umbrella.”