Strategically placed garden plants offer a low-cost way to cool homes in summer

Climate change is bringing extreme summer heat to many more countries, but using the right plants in your garden could help keep your home a bit cooler next summer.

As the fall planting season begins, this is a good time to plan for next summer. Planting now can also help your climbing plants and shrubs get established before spring.

After the 2026 heat waves, many people are looking for ways to cope with very hot days that have started to happen more regularly . But that doesn't have to mean investing in an expensive air conditioner.

Anyone with a garden, or even a balcony, could have a much cheaper answer. Plants are nature's own air conditioners .

Plants mitigate excess heat in three main ways. They create shade, reducing the sunlight absorbed by hard surfaces such as roads or driveways and then radiated back as infrared radiation (heat).

They also use light to evapotranspire—converting liquid water into vapor—and this dissipates energy without raising the temperature. This keeps plant tissues and their surroundings cool.

Third, depending on their leaf properties (color, texture, waxiness or hairiness), some plants reflect incoming solar radiation back into space (the albedo effect), preventing this energy from becoming heat. Silver-leaved plants are thought to be particularly good at this, including Colorado spruce, blue fescue grass and lamb's ear.

Researchers have known for many years that plants can both cool a building in summer and insulate it from cold in winter . But many of the systems promoted for commercial buildings— green "living" walls and green roofs —are relatively expensive and difficult for the average homeowner to build.

Yet plants provide the same benefits whether they are part of a sophisticated architectural feature or simply garden plants positioned to beautify the house or provide food for the household. Indeed, some of the most effective passive cooling systems for homes involve plants such as climbing plants (vines), wall shrubs or trees strategically placed to block the sun in summer.

Whether they are roses, wisteria and clematis that enhance the atmosphere of an English cottage garden or cherries, apples and tomatoes that provide food for the dinner table, plants trained against a house have a cooling effect directly on its walls and indirectly on its interior .

My research with colleagues has shown that placing plants in front of a south-facing brick wall can reduce surface temperatures by as much as 25°C . But some types of plants cool better than others. There is a hierarchy of coolness. Ivy and honeysuckle are consistent coolers, whereas winter jasmine and rockrose are less effective across a range of weather conditions. All plants cool through shade and evapotranspiration, but some do a better job than others.

This has practical implications . With plants that cool primarily through shade, the aim is to maximize the amount of foliage between the sun and the wall. These plants have naturally large, dense canopies, such as cherry laurel and evergreen viburnums.

Almost the opposite is true for plants that cool through transpiration, such as hydrangea, fuchsia and clematis. Their thin veil of leaves optimizes cooling performance. They depend on a reliable source of water, though, so they may not be the best choices if your area has regular hose-watering bans.

In practice, a mix of wall shrubs and climbing plants grown against a south-facing wall provides visual appeal and a range of cooling strategies. Leaving an air gap between the plant and the wall enhances heat insulation. Planting the shrub 0.5 meters (1.5 feet) from the wall or growing climbing plants on a wooden trellis set away from the wall is ideal for this.

It is not just the house that benefits. Careful design with plants that provide shade and evapotranspiration can make a patio or children's play area more comfortable. We are also investigating whether movable potted plants can provide localized cooling in front of glassed-in areas, such as French windows and sunrooms, or on south-facing balconies.

Creating a green facade for your south-facing walls is far less expensive than installing air conditioning and better for the environment because it doesn't produce emissions or heat the air.

Climbing annuals (nasturtium, morning glory, sweet peas, thunbergia), tall flowering annuals (sunflower, larkspur, cosmos), biennials (foxglove) and short-lived perennials (hollyhock, rudbeckia, mullein, delphinium) can work as well as perennial shrubs and climbing plants. They can all be grown from seed (£2–£3 per pack).

For those with a bit more cash to spare (£10–£20 per plant), perennial climbing plants can also be a good value because they can last 15–20 years. These include roses, passionflowers, clematis, solanum, wisteria, ivy, summer-flowering jasmine, perennial peas and honeysuckle.

As a bonus, these plants look wonderful, sometimes smell fantastic and are not noisy. Who ever said that of an air conditioner?