Newly planted trees should be watered differently than mature ones. (PhotoDisc)
The weather has taken a terrible toll on the trees in our landscapes in the past couple of years. Storm damage, winterkill and drought are all factors. And drought-stressed trees attract pests and disease.
One of the best things we can do to help our trees defend themselves is keep them watered.
Most of the feeder roots that take up moisture for established trees reside in the top 4 to 10 inches of soil, and as trees mature, the roots spread well beyond their canopies. If not watered in an extended drought, the fine root hairs die, putting the root structure of the tree out of balance with the canopy, and leaf and needle loss and branch dieback result. It can take two to three years for trees to show the effects of drought stress.
Wilting, leaf loss, early coloration, needle drop, discoloration and/or scorching of leaves are all indications of lack of water.
The technique for watering a newly planted tree is much different than an established tree because all the roots of new trees are located in the rootball. Because the roots are sucking water from that area, the root ball will dry out more quickly and should be watered more frequently than established trees or shrubs in the area. In high heat, that may be twice a week.
Putting a bubbler or sprinkler at the base of a mature tree is not effective and can cause disease. Better to set the sprinkler so the water pattern hits the outer half of the area under the canopy and beyond. A mature tree can develop a root spread of 1½ to 4 times the width of the canopy.
Mature trees should be watered to a depth of 18 to 36 inches. Shallow watering can result in surface root development.
There are no rules regarding how long or often trees should be watered because the soil in every landscape is different. Tree roots need oxygen as well as water to thrive, so watering until the ground is sodden can cause root rot. Clay soil drains slowly and holds water longer than sandy soil. I use a moisture meter to measure the depth of saturation.
Appearances: Join me on the Grosse Pointe Garden Walk from 2-4 p.m. Saturday. I will be with perennial expert Susan Martin in the garden of Peter and Kelly Oliver to answer your garden questions. Garden walk tickets are $12 pretour and $15 on tour day. For information, call the Grosse Pointe War Memorial at (313) 881-7511.
Nancy Szerlag is a master gardener and Metro Detroit freelance writer. Her column appears Fridays in Homestyle. Email her at Szerlag @earthlink.net. You can also read her previous columns at detroitnews.com/homestyle.