Thursday, July 24, 2008
Wet's bad for dogwoods, sap's fine by maples
John Arbogast
Landscape consultant John Arbogast answers your questions every Thursday. Send questions about your lawn, garden, plants, or insects to:
Dear John
5102 Greenfield St. SW
Roanoke, Va. 24018
Or send an e-mail. Answers will be given only in this column. Please don't send pictures or samples.
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Q: One of our mature dogwoods next to our house has droopy leaves. We have had a great deal of rain this year. Is it true that dogwoods do not like too much root dampness and this condition can cause droopy leaves? If so, what can be done to fix the problem?
A: Something is interfering with water movement up from what should be an adequate system of healthy roots through the trunk and branches to the leaves. Or heat around the plant is causing leaf pores to give off more water than the roots can replace.
I have not heard that dogwoods do not like too much root dampness. But it is true that too much root dampness can cause droopy leaves on most woody landscape plants. In such cases, excessive water in the soil pushes out the needed air between tiny soil particles as water fills the tiny soil pores formerly occupied by air.
In your case, there was probably more moisture accumulating in the soil next to your house than in other parts of your landscape.
When that happens, roots can’t function or will rot. Either will cause the leaves to droop.
Organic mulch piled too deeply over the base of a tree can cause the same results because the thick blanket keeps the roots constantly damp. In Roanoke, we have a lot of water-holding clay in our soil and organic mulch should be no deeper than 2-1/2 inches thick. So clear out any mulch.
Has there been injury to the trunk? If so, that'll hinder movement of water from the roots up to the leaves and can cause leaves to droop. Unfortunately, dogwood wounds don’t heal well naturally, so damaged dogwoods might need replacing.
A dogwood located near a gutter downspout will be troubled by excessive water. If this situation exists, redirect downspout flooding by adding black plastic hose to carry off the water elsewhere.
Q: We have several 40-year-old sugar maples throughout our large yard that we’re having pruned and shaped. Half of them were pruned during mid- to late winter four years ago, and we plan to have the rest of them pruned during the coming dormant season. I want to know what we should be doing now and during the fall and winter to prevent the problem that occurred with the maples right after cutting branches the last time. Sap dripped or flowed out of most of the cut ends that caused us, neighbors and visitors to become concerned. We thought the maples had become infected by the pruning tools used. Our place is in the lower elevations of the Blue Ridge Mountains.
A: Trimming caused the sap to rise but before new leaves emerged, and that's a natural thing for maples.But this sap loss does not harm the tree.
Let the sap flow for now. However, have the pruning and shaping done in the fall immediately after the leaves have changed color and dropped. This is nature’s signal that the maple is dormant and the sap has ebbed. Sap pressure will be much lower in the trunks and branches then, and flow from openings is less likely.
Spend time in the weeks ahead looking for the most knowledgeable tree professionals who can do the work for you this fall. Ask to see some of their previous work.
