Smart watering keeps mature trees lush and healthy all summer - LandSteward Article

The Plant Man column for publication week of 06/19/05 - 06/25/05 (664 words) ###
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 trees during their first summer months. But let's not forget that mature trees, whether they are young adults or senior citizens, need your attention too.
Maybe it goes without saying, but I'll state the obvious anyway: trees need water. Water helps a tree manufacture its "food" and provides the conduit to
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 tree,
weighing many thousands of pounds, sweltering under the summer sun. Large trees can lose a lot of water. How much?
Take, for example, an oak tree that is 90 feet tall with a 90 foot canopy spread. When the temperature reaches 90 degrees Fahrenheit, the tree can lose up to 90 gallons of water in a single day! That's according to David Robson, Extension Educator / Horticulture at the University of Illinois, writing in an online article on summer tree care.
You can read that entire article at and you can
click on a direct link when you go to my Web site and find this column under the Plant Man heading. You can also find hundreds of
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, you might be surprised to know that the roots that absorb most of the water are located only about fifteen inches or so below the surface. These are called
feeder roots and most of them are NOT located at the base of the trunk, but rather at the tree's drip line.
However, the feeder roots of a large, mature tree can extend well beyond the
dripline, and can be quite fine, even hair-like. Drought-like conditions can dry out these delicate feeder roots. When Nature isn't providing the necessary moisture in the form of rainfall, your mature trees will welcome your assistance.
It is far better to provide sufficient water in a single, saturating application than to apply the same amount of water over several, shorter applications. Why is this? Several short waterings are likely to draw the feeder roots towards the surface where they can dry out and wither as the sun dries the soil.
Single saturation soakings encourage growth of feeder roots deeper below the
surface where the soil temperature is also cooler.
Mr. Robson's article reminded me of an old landscaper's trick. If you're using a sprinkler, place an empty tuna can (approximately one inch deep) at the tree's drip line. Check the can from time to time as the sprinkler does
its work. When the can is full, empty it and allow it to fill up one more time.
In my previous column (archived at my Web site, in case you missed it) I specifically addressed the watering needs of new, young trees. But how much water should you expect to apply to more established trees? Here's a handy 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 the trunk and eyeball it.
Keep an eye on the rainfall this summer, either using a rain gage or getting
information from local news sources. Supplement Nature's shortfalls with a 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 and landscaping to and for resources and additional information, or to subscribe to Steve's free e-mailed newsletter, visit
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