The Plant Man column
for publication week of 06/19/05 - 06/25/05
The Plant Man
by Steve Jones
Smart watering keeps mature trees lush and healthy all summer
In this column last time, I discussed the special needs of new, young
during their first summer months. But let's not forget that mature
whether they are young adults or senior citizens, need your attention
Maybe it goes without saying, but I'll state the obvious anyway: trees
water. Water helps a tree manufacture its "food" and provides the
flow that food through its system. Additionally, water provides the
essential coolant to help a tree cope with the summer heat.
If you go to the gym and work out, you know how quickly you can lose
moisture and how important it is to replace it. Now think of a mature
weighing many thousands of pounds, sweltering under the summer sun.
trees can lose a lot of water. How much?
Take, for example, an oak tree that is 90 feet tall with a 90 foot
spread. When the temperature reaches 90 degrees Fahrenheit, the tree
lose up to 90 gallons of water in a single day! That's according to
Robson, Extension Educator / Horticulture at the University of
writing in an online article on summer tree care.
You can read that entire article at
http://www.urbanext.uiuc.edu/greenline/98v3/gl9807.03.html and you can
click on a direct link when you go to my Web site www.landsteward.org
find this column under the Plant Man heading. You can also find
direct links to other useful garden and landscape information at my Web
Although some of a mature tree's roots can be quite deep in the ground,
might be surprised to know that the roots that absorb most of the water
located only about fifteen inches or so below the surface. These are
feeder roots and most of them are NOT located at the base of the trunk,
rather at the tree's drip line.
However, the feeder roots of a large, mature tree can extend well
dripline, and can be quite fine, even hair-like. Drought-like
can dry out these delicate feeder roots. When Nature isn't providing
necessary moisture in the form of rainfall, your mature trees will
It is far better to provide sufficient water in a single, saturating
application than to apply the same amount of water over several,
applications. Why is this? Several short waterings are likely to draw
feeder roots towards the surface where they can dry out and wither as
sun dries the soil.
Single saturation soakings encourage growth of feeder roots deeper
surface where the soil temperature is also cooler.
Mr. Robson's article reminded me of an old landscaper's trick. If
using a sprinkler, place an empty tuna can (approximately one inch
the tree's drip line. Check the can from time to time as the sprinkler
its work. When the can is full, empty it and allow it to fill up one
In my previous column (archived at my Web site, in case you missed it)
specifically addressed the watering needs of new, young trees. But how
water should you expect to apply to more established trees? Here's a
rule-of-thumb, with trunk diameters (calipers) shown in parentheses:
Small to medium trees (1" - 9"): 10 gallons/inch
Large trees (10" and up): 15 gallons/inch
If you are unsure of your tree's diameter, simply place a ruler against
trunk and eyeball it.
Keep an eye on the rainfall this summer, either using a rain gage or
information from local news sources. Supplement Nature's shortfalls
watering program and you'll be enjoying lush, green trees for many more
The Plant Man is here to help. Send your questions about trees, shrubs
landscaping to email@example.com and for resources and additional
information, or to subscribe to Steve's free e-mailed newsletter, visit