Select the right trees and they'll survive the "hot spots"

The Plant Man column for publication week of 07/17/05 - 07/23/05 (712 words) ###
The Plant Man by Steve Jones
Select the right trees and they'll survive the "hot spots"
It's summer, and that means it's HOT. What do you do when you get hot? Probably, you go indoors to relax with a cool drink in air-conditioned comfort.
But spare a thought for your trees. They are literally stuck outside with no choice but to swelter in the heat. There's not much you can do about the
weather. However, when it comes to helping trees survive and thrive, there are two important elements that you can control: WHAT you plant and WHERE you plant.
Today, I have some suggestions for trees that are more resistant to heat and drought conditions. But first, it's a good idea to think about where you will be planting your new trees. Where are trees likely to be exposed to the most heat?
=> Concrete and asphalt absorb and radiate heat and can be anywhere from 9 to 12 degrees hotter than nearby woodlands. Because concrete and asphalt cool slowly, heat continues to radiate even after sundown.
=> Walls of buildings (especially on the south and west sides) get hot and reflect that heat directly to the area in front of them.
=> Road traffic creates heat. In addition to the heat shimmering off the blacktop, busy roads and parking lots are full of cars and trucks generating heat from gasoline and diesel engines. Temperatures can reach 120+ degrees.
=> An open expanse, such as a very large lawn or parkland, will be hotter that a woodland area where crowds of trees provide mutual shade and leaf litter forms a natural mulch to maintain cooler soil.
So... we know that trees will do better when NOT subjected to the conditions
I described. But when we have no choice in the matter, it makes sense to plant trees that are more likely to tolerate conditions of heat and possibly drought. There are plenty to choose from, but here are some that come to mind:
Red maple (Acer rubrum). Here's one that can tolerate urban conditions. It's an excellent specimen tree with red blooms in the spring and breathtaking fall foliage. An excellent shade tree.
Green ash (Fraxinus pennsylvanica). A street-tough urban warrior that can take the heat and is also wind-tolerant. Ideal for parks, parking areas or close to streets, it can reach heights of 50 - 75 feet.
Cherrybark oak (Quercus falcata). A fast-growing red oak with modest water requirements, it develops a dark grey or black bark at maturity. It produces small, rounded acorns that can attract wildlife.
Colorado blue spruce (Picea pungens). This evergreen is a good choice for a 'screen' when a row are planted approximately 6 feet apart. It seems to do equally well in full sun, partial sun or shade and prefers soil that's somewhat on the dry side.
Even after you've selected heat-resistant trees, you cannot "set 'em and forget 'em" to borrow a phrase. Water is essential to these tough guys, too.
I recently wrote two columns specifically about the best way to water young and mature trees. You can find them archived at my Web site. Go to then click on "The Plant Man" header and scroll down to find the columns.
Just as Nature keeps the soil cool and moist with leaf litter around trees, mulch can perform the same function. Add 2" to 4" over the tree's plant zone. You'll help to prevent moisture evaporation and water runoff and discourage weeds and other plants from competing for what moisture there is.
Fertilizing a new tree might seem like a good idea, but don't do it unless a soil test indicates a serious need. Reason? Nitrogen can cause a growth spurt and new leaves can quickly wilt and die because of heat stress.
There's an excellent online resource titled "Trees for Problem Landscape Sites" produced by the Virginia Cooperative Extension. It includes planting and maintenance advice, tree suggestions and is illustrated with photographs. The address is and you can click on a direct link when you find this column at my Web site.
The Plant Man is here to help. Send questions about trees, shrubs and landscaping to For resources and additional information, or to subscribe to Steve's free e-mailed newsletter, go to
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