Monday, September 19, 2011

A Burning Question

This summer, I planted a new crape myrtle inside a walled, sun-blasted courtyard. With little root system to sustain it, the young shrub wilted badly under temperatures that reached 100F to 110F degrees in the shade day after day. Tender leaves began to go brittle.

With unrelenting, record-setting heat for three months running, this summer has been especially brutal to even established landscape plants. I've seen outer leaves on the crowns of mature Japanese maple trees fried to a crisp. And then there are the sunscorched evergreen hedges grown next to reflective surfaces.

A wall—or even a parked vehicle—exposed to direct summer  sunlight can turn that area into a broiler. Any plant grown in close proximity to reflective surfaces during periods of extreme heat is in danger of scorching. For low-growing plants, there is a short-term remedy.

Once I began tossing a sheet over my crape myrtle during the heat of the day, it perked up and made it through the summer in good shape. Low-growing hedges can benefit from the same protection. (Plants growing near reflective surfaces need more water, but watering won't prevent sunscorch.)

Unfortunately, there isn't much you can do about a large tree that is suffering sunscorch, other than make a better choice of species the next time. Most trees that suffer burned foliage during extreme heatwaves are either too tender for such extremes—or are understory species, adapted to filtered sunlight, that were planted out in full sun.

As summer draws to a close, it's time to take stock. If sunscorched  twigs are brittle, they've died and need to be pruned away. If the twigs remain flexible, wait until spring to see if they sprout new foliage. If the same problem occurs summer after summer, the long-term remedy is to remove the plant and replace it with a more heat-tolerant species.

As for my crape myrtle, I expect the fast-growing crown to be above the top of the courtyard wall by next summer, safely out of range of the reflected heat.

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