Using living plants to control energy costs

Story and Photography by Helen Newling Lawson

Everyone knows how soothing a carpet of green grass feels on bare feet or how the shade of a large tree offers relief on a summer’s day. But did you know you could harness the cooling effect of living plants to control energy costs inside your home? 

And not just by a little. “Green” walls can lower reduce energy costs by up to 30 percent and lower the temperature behind them by 10 degrees Celsius. The cooling effect from plants can be particularly beneficial in urban “heat islands.” But a green approach to heat control can also be used anywhere the sun bakes down on a home, patio, driveway, play structure, or outbuilding.

Coral vine is a showstopping backdrop and a serious pollinator. It’s also a highly heat-tolerant choice for cooling hot walls.

Dense plantings like green walls, vines trained to a trellis, or even a row of evergreen shrubs trap a layer of insulating air to reduce temperature fluctuations. Without plants, the surface of a wall can fluctuate 50-140 F. With green walls, that range is reduced almost by half, keeping the temperature inside the walls more stable as well. Green barriers can also reduce the effect of wind, UV radiation, and rain on the building’s exterior, limiting the damage to energy-efficient building materials. 

Vines trained up a wire trellis along a wall help reduce the heat inside the building and limit reflected heat onto the plants in the rest of the bed.

Using plants to create natural cooling extends other environmentally friendly benefits beyond lower energy consumption. A lower power demand for mechanical cooling systems also means fewer polluting byproducts are released into the air. Plants also help improve air quality by acting as natural filters, trapping particulate matter and gases. 

Plants can help cool horizontal surfaces, too. Where possible, replace mulch or concrete with ground covers. A drought-tolerant ground cover will require less water general upkeep than lawn. A border of ground cover or low shrubs near paved areas can help reduce the reflected heat. 

Arbors and other structures planted with vines help to create shade to keep sitting areas comfortable.

Plants for Hot Spots
As you would imagine, where concrete or other building materials reflect sunlight can get quite a bit hotter than the surrounding area, so you will need to choose plants that can tolerate higher temperatures. 

Coral vine (Antigonon leptopus) – This vine thrives in hot spots, and is highly drought tolerant once established.

Citrus trees – If you have space to roll their containers to a protected area in the winter, citrus trees provide fragrant blooms and tasty fruit on a highly heat-tolerant plant.

Mangave – This cross between Manfreda and Agave is relatively new to the scene, but is already available in a range of exciting textures, colors, and sizes to lend serious structural interest and exotic appeal to your garden. But despite their otherworldly appeal, they are native to North America (although only hardy to Zone 8), and deer and drought tolerant as well. 

Rock verbena (Glandularia pulchella) – This charming semi-evergreen ground cover is covered in dainty purple flowers but thrives in high-heat situations. 

Staying Warm When Temperatures Drop
Plants can help control winter energy costs, too. Tall deciduous trees will shade your roof in summer but allow the sunrays to provide solar heating in winter. If you have space, plant a windbreak of conifers or other dense trees farther from your home to slow winter wind. These steps can reduce winter heating costs by up to 25 percent.

The plants alongside this paved area in full sun need to be able to handle the added reflected heat.



Nature’s Helpers
What else can plants do for cities?

• Improved air quality – indoors as well as outdoors – is just one positive by-product of green cooling systems. Cities and other manmade structures also benefit in other ways. 
• “Nature breaks” – City dwellers find respite in even small pockets of green
• Privacy without the solid barrier of walls
• Noise reduction
• “Rest stops” offering food and shelter to migrating birds
• Microhabitats for pollinators and other wildlife
• Increased biodiversity – the more species of plants in an area, the more species can be supported.
• Opportunities for “urban farming” 
• Local job creation – from growing to installation and maintenance, an increased demand for urban plantings can grow jobs, too.

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