University Of Sheffield Researchers Detail Cooling Benefits Of Climbing Plants; And A New Very Dark-Coloured Sedum
by Art Drysdale
by Art Drysdale


Art Drysdale, a life-long resident of Toronto and a horticulturist well known all across Canada, is now a resident of Parksville, British Columbia on Vancouver Island, just north of Nanaimo. He has reno-vated an old home and has a new garden there. His radio gardening vignettes are heard in south-western Ontario over radio station Easy 101 FM out of Tillsonburg at 2 PM weekdays.

Art also has his own website at

February 2, 2014

Sedum ‘Touchdown Teak’ a new gorgeous foliage colour for the tried and true sun-loving perennial. Photo courtesy Terra Nova Nurseries.


According to Matthew Appleby writing in the on-line January 24 edition of the U.K. Horticultural Trades Association (HTA) journal, “wall shrubs and climbers can provide ‘significant passive cooling’ with wall temperatures behind the plant canopies up to ten degrees C cooler, HTA research has found.

“Experiments by HTA-funded PhD student Jane Taylor, led by University of Sheffield senior lecturer in landscape management, Ross Cameron, used a replicated wall system outdoors. It showed that during warm weather, walls screened with evergreen cherry laurel (Prunus laurocerasus) were ten degrees C cooler than the surface of bare walls.

“Air next to the walls was three degrees C cooler than nearby bare walls. On clear sunny days, walls screened by plants were significantly cooler between 11 am and 6 pm, with the greatest differences in mid-to-late afternoon. Ross Cameron said species such as jasmine, honeysuckle and fuchsia may be better ‘cooling’ plants than ivy be-cause their leaves are more effective at cooling the surrounding air.

“‘This is probably good news for the industry because the implication is that many of our highly ornamental and attractive flowering climbers are likely to have positive functional benefits to the wall too,’ he suggested.

“Taylor said the research adds weight to the argument that plants could be used to reduce buildings' energy loads by partially substituting for artificial, mechanized air cooling. Brick was chosen as the building material to help demonstrate the potential of plants to provide summer cooling and winter insulation to older domestic housing stock, where retrofitting by other means can be difficult.

“The research also emphasized that not all ‘green infrastructure’ should be treated in a generic manner by policymakers and practitioners. A range of controlled-environment studies showed that different plant species have different capacities to cool wall surfaces, and the mechanism by which cooling occurred could vary between plant species.

“Cooling due to the presence of fuchsia, for example, was strongly reliant on evapotranspiration, whereas ivy (Hedera), honeysuckle (Lonicera) and jasmine (Jasminum) cooled primarily through shading. Prunus cooled via both shade and evapotranspiration.

“Although not normally considered a wall plant due to its short stature, lamb's ear (Stachys byzantina) was included in the study to assess the effects of hairy, silver leaves. This species was surprisingly effective at cooling with mechanisms being attributed to shade, evapotranspiration and an albedo effect--the silver leaves reflecting back light from the wall environment.

“Another important factor in optimizing the cooling effect was the thickness of the foliage. Developing a uniform facade of full transpiring leaves may be more promising than developing a thick, deep canopy of foliage where the leaves self-shade each other.

“Green facades lend themselves well for domestic properties. Little previous research documented cooling ad-vantages in a temperate climate.

“PhD student Jane Taylor's thesis also showed very strong positive effects of green walls' plants on providing insulation to walls in winter.”

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Just to conclude this week, here is a glimpse of another new herbaceous perennial, Sedum ‘Touchdown Teak’. It comes from the famous Terra Nova Nurseries in Oregon. There are actually four different colours in the ‘Touch-down’ series, I think ‘Touchdown Teak’ is simply the most dramatic.

The 'Touchdown' varieties of Sedum were bred to have a vigorous multi-crown habit, making them ideal for growing in containers. 'Touchdown Teak' has vibrant red-brown to purple-brown coloring and thick glossy coating, giving a shining, silver-to-bronze appearance to the leaves. These waxy, slightly scalloped leaves keep their unique leaf color all season. If you're looking for a super-easy perennial that tolerates drought, heat, poor soil, humidity, and cold--while still producing beautiful red foliage season after season -- 'Touchdown Teak' is the one you want!

Bright crimson flowers come on in midsummer, towering 22 cm (9”) over the 20 cm low bush. As summer turns to fall, the color changes to a mellow (yet vibrant!) coppery-orange, and it remains on the plant well into winter, holding the snow in nice little sculptures. Of course, before the seasons change, butterflies, bees, and birds all take turns feasting on these blooms. And if you'd rather enjoy the winter color indoors, cut the blossoms while they're fresh, hang them upside down until they dry, and enjoy red everlastings for months!

Again, 'Touchdown Teak' grows just 20 cm (8”) high and quickly spreads to form a carpet 40 cm (16”) wide, ideal for the container, and just as well-suited for the center of the perennial border, edging the driveway, or cutting a ribbon of color through the shrub planting! The habit is tight and compact, with multiple crowns peek-ing out right at ground level.

Sedum is famous for its ability to put up with just about anything in the garden, and 'Touchdown Teak' is no exception. Give it full sunshine and reasonably good soil drainage, and it will do the rest! Be sure to pamper it the first year with plenty of food and water, getting its root system established. Then let it go and watch it flourish! Very tolerant of all kinds of conditions once established, this naturally-healthy plant does not need the help of any chemicals.

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