Taken from Eclectic Gardener @ www.teachinggarden.org
Written by Alan Hickman

In old Brampton, where the trees are fifty and more feet high and as many or more years old, the trees can cope with drought pretty well. However, with most of Brampton now newly built, when temperatures rise to the high twenties and thirties for extended periods, attention needs to be given to the thousands of trees that have been planted over the past decade or so.
While established lawns go dormant and have no need for water during hot weather, young trees, even if their leaves don’t become dull and wilted, can have their development noticeably retarded by drought.
As most trees are planted in lawns, the first thing to do is to separate the trees from the grass. In nature, trees and grass do not cohabit well; in fact grass and trees have been in a state of war for millions of years.
Grass does not grow in forests and trees scratch a poor living on the plains. On the relatively rare occasion when a tree has grown in isolation, the branches naturally droop down to ground level and shade out grass and undergrowth. The area beneath the canopy is usually bare except for a protective covering of twigs, leafy bits and sundry wind-blown debris.
Grass and trees engage in a form of chemical warfare called allelopathy: the direct influence of a chemical released by one living plant on the development and growth of another. A well-know example of allelopathy is the effect of the chemical ‘juglone’ which is released by walnut trees to inhibit the grown of competing plant species. Grasses synthesize chemicals which tend to retard tree growth and the younger the tree, the more pronounced is the effect.
Separating trees from grass does not mean digging up the soil and planting petunias in a circle! Apart from constantly disturbing the tree’s roots, the esthetic effect is much the same as dressing up a poodle in pink booties and a pearl necklace.
Encouraging what nature is going to do anyway is usually the most effective way to garden, and nature’s way with trees is to use copious amounts of mulch in various stages of decomposition. For a small recently- planted tree, the mulch should cover an area at least six feet in diameter. As the tree grows, the mulched area should expand to follow the drip-line, roughly the circle under the outermost tips of the branches.
Having a young tree properly planted is half the battle and, if properly planted, the trunk/soil juncture will be two or three inches above the general lawn level with a gentle slope away from the trunk. As a tree’s feeding roots are often just below the surface, it is best not to try digging up any existing lawn. Either leave the grass where it is, and rely on the mulch to smother it, or give the area a spritz with Roundup a couple of weeks before putting the mulch in place.
If it is available, first, evenly spread about an inch of coarse, partially rotted, compost over the area to be mulched. Cover that with three or four inches of shredded wood-chips - the sort of thing the City produces from tree prunings. The compost layer will act as a bit of a sponge, releasing moisture between rainfalls, and it will tend to make up for nitrogen used as the woody mulch begins to decompose. The final effect should be a fairly flat area of mulch with perhaps a slight outward fall. (see photo references on muching, the good and the bad)What should be absolutely avoided is the weird ‘volcano effect’ in which mulch is piled up like Mount Vesuvius with a tree trunk erupting out of the crater. Apart from looking grossly unnatural, creating a depression around a tree’s trunk is just asking for bark damage. In summer, rain will sink straight through the mulch but in winter, when the wood-chips freeze into an impervious solid, water, from a spring thaw or an early shower, will accumulate and re-freeze in the saucer. The pressure from freezing water can damage the conductive tissue of any tree and young trees are particularly susceptible.
Watering a properly mulched tree is simplicity itself. Use a fifty foot length of black porous soaker-hose and spiral it a couple of times around the outer edge of the mulch. Let the water seep out for as long as it takes to apply about two inches of water depth. An easy way to find out how much water is coming out of a soaker hose is to insert a tuna can into the mulch under the hose and measure the accumulation. If the can collects half an inch in an hour, it will take four hours to apply two inches of water to the area under the hose. A couple of inches of water once a month should keep most trees happy, but if a tree has only been in for a few weeks, then an inch a week is likely a better idea.