What you need
An ivy plant
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A wall
A pot (optional, but recommended)
THE latest thing in architecture is green buildings 鈥� covering walls and roofs with a carpet of plants to insulate, soak up rain and provide a home for wildlife. Many such buildings need complex systems for holding and irrigating the soil, but there is a much easier approach: growing some ivy.
Ivy is a group of about a dozen species of evergreen climbing plants in the genus Hedera that are happy in shade or full sun and with most kinds of soil. They don鈥檛 need supports as they grow aerial roots that latch on to most things. Many people use ivy to quickly cover an ugly wall or fence. It also provides nectar for pollinators and its berries are a valuable food source for birds in winter.
In a temperate climate such as the UK鈥檚, an ivy covered wall will slightly warm a room in winter. As well as insulating, ivy cools a room in summer through shading and by water evaporation from its leaves. 鈥淚t cools the surrounding air. It鈥檚 like sweating,鈥� says Tijana Blanu拧a at the University of Reading, UK, who has examined the insulating effects of climbers. She and her colleagues that Hedera helix ivy created a larger cooling effect than two other climbers, Boston ivy (Parthenocissus tricuspidata) and climbing hydrangea (Pileostegia viburnoides).
This is probably because its leaf cover is so dense, says Blanu拧a. Hedera helix鈥榮 exact cooling effect is hard to quantify as it depends on so many factors, but it could be by a few degrees, she says.
Ivy has a reputation for damaging buildings, but according to the UK鈥檚 Royal Horticultural Society, this doesn鈥檛 usually happen unless they already have cracks 鈥� the aerial roots . The other fear is that it can make walls damp, but Blanu拧a鈥檚 study found that ivy raised humidity next to the wall by only a small amount. You do need to be careful, though, as once ivy has been in the ground for a few years, it can grow like billy-o. In some parts of the US and Australia, certain kinds of ivy are classed as invasive weeds.
I can empathise, having had a few battles with ivy plants that I let get out of control. If it reaches the roof, it can get under tiles and block gutters. So don鈥檛 plan on covering a wall with ivy unless you are willing to get up a ladder twice a year to cut off any shoots that are approaching danger zones. One option is to paint vulnerable structures with anti-graffiti paint that contains a chemical called silane. This of the plant鈥檚 aerial roots.
Because of ivy鈥檚 vigorous nature, I also wouldn鈥檛 recommend planting it in a flower bed with the intention of covering a fence or shed, as you will be forever pulling out shoots trying to take over the patch. Instead you could use a large pot or confine it to a small patch like I have done, by lifting a few bricks from my patio, and planting the ivy in the exposed soil underneath.聽You just have to keep the upper hand.
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