Nurture that shade tree to stay cool all summer

If I had to choose one plant to have in my yard at this time of year, it would be a tree. Preferably, it would be a shade tree, one that would be big enough to shelter me, my house and a few choice plants from the sweltering rays of the sun.

There is nothing quite like walking into the shade provided by a large tree on a hot day. It is immediately 10 to 12 degrees cooler. The shade is dark enough to stop the squinting you've been doing. With some trees, enough moisture is given off by their leaves to feel even cooler. With all the benefits given to us by trees at this time of year, the gardener should make a concerted effort to repay this kindness by properly caring for them during the stressful summer months.

The first question most gardeners ask is how to water a tree during the summer. The answer depends on many factors, of course. Is the tree in full sun or is it growing in the shade of buildings or other trees? Is it in the lawn where it is already receiving some water? How established is the tree? Is it a drought-tolerant tree or is it a water-loving species? Once you have identified what you have, you can begin to understand its needs.

Trees that are out in the open, especially if they are subject to drying winds, will need more water than their sheltered counterparts. A good rule of thumb is that trees will need about 11/2 inches of water per week in the heat of summer. Some will need more, some less, but that's a good place to start with many trees. Run your sprinkler long enough to put a half-inch of water into a tuna can and you'll know you'll need to water three times that long each week when it heats up.

If the tree is growing in an area that it shares with lawn, remember that there is great competition between tree roots and grass roots for the food and water that you put there. While you are applying a couple of inches weekly for your turfgrass, be sure to factor in that extra inch that the tree will need.

A great method of providing this water is to lay out a soaker hose halfway between the tree trunk and its dripline and to let the hose run for several hours. This will provide the extra water necessary for the tree roots without applying excess water to the turf. This area should be in mulch, so it won't be necessary to put the hose away between waterings.

Avoid causing stress to trees at this time. Summer pruning can be invasive and deadly if you are heavy-handed. Unless you're a pro, keep the saw in its sheath until cooler weather returns.

If you have planted a new tree this spring, it will need approximately 15 gallons of water a week if it is an inch to an inch-and-a-half caliper size. Drill a hole, an eighth-inch or smaller, in the bottom of a 5-gallon container and fill it and move it around the tree in three spots to complete the watering. You can do this over several days if you like. It's the total water per week that matters.

Mulching the root zone of the tree is one of the best practices that you can follow to ensure the survival of trees. It eliminates the deadly wounds caused by overzealous weed whackers. It holds moisture in the soil while it keeps it cooler. It adds organic matter to our poor soils over time. Just be sure not to pile mulch up against the trunk.

Don't over-apply mulch to depths more than 4 inches. In fact, 2 inches is all most trees will need. Never put plastic or weed-block fabric under the mulch. With our hot summers, I don't recommend the use of inorganic mulches like stone because they will retain heat.

This watering regime applies to planted, horticultural trees only. Native trees such as our ponderosa pines and madrones need to be handled differently. Next week we'll talk about survival strategies for them.

Stan Mapolski, aka The Rogue Gardener, can be heard from 9-11 a.m. Sunday mornings on KMED 1440 AM and seen in periodic gardening segments for KTVL Channel 10 News. Reach him at

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