The Plant Man column
for publication week of 07/17/05 - 07/23/05
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
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
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
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
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 www.landsteward.org 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
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
http://www.ext.vt.edu/pubs/nursery/430-024/430-024.html 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 firstname.lastname@example.org For resources and additional
information, or to subscribe to Steve's free e-mailed newsletter, go to