Prolonged drought effect on established and newly planted trees.....
Many of you may have noticed significant tree dieback or total tree death this past growing season. Some of this is due to the widespread drought, and some is due to drainage problems on new construction sites consisting almost entirely of excavation and fill soils. The primary significant difference between drought damage and drainage problem damage is the symptoms the tree exhibits as it dies. The way to tell if you have damage due to drought or drainage is that a drowned out tree will not drop their leaves, drought trees do. When faced with a drainage problem, the leaves will discolor and look like it is wilting or dry when it is actually suffocating and drowning. The leaves will turn yellow and/or brown, become wilty and remain on the tree. This page primarily addresses drought problems. Click for drainage problems.
In order to understand some of the problems we are seeing this year, a overview of last years precipitation patterns is necessary.
The spring of 2011 was characterized by frequent rainfall throughout the months of May, June and early July. This was common throughout eastern SD, western MN, and throughout the Northern Plains. The preceding years annual rainfall was well below average for this area, therefore there was no excessive subsoil moisture present. We did however have adequate topsoil moisture for the Spring of 2011, due to above average rainfall and snowmelt.
No significant moisture fell after early July 2011.
That trend continued until April of 2012. Many homeowners did not continue providing moisture throughout late summer, fall or early winter. Many even refrained from watering their lawns on the assumption that if their lawn was dormant, it would wake up just fine in the spring, as it always had previously. The lack of snow cover was even more damaging, as trees, shrubs, perennials, and lawns had no protection from winter dessication. Add in the factor that many new homes have inadequate topsoil, or compacted soil, and you have the recipe for major damage to lawns, trees, shrubs, and other ornamental plantings. An important fact to remember is that lawn irrigation is just that. It is designed to put small amounts of water over a large area frequently, but not deeply. As a result, you have very shallow rooted turf, trees and shrubs.
Trees in a landscape 5 years or less are most susceptible to drought, as well as trees planted in highly compacted modified soil sites.
After 2 years of drought larger trees will be impaired. The first signs of drought in larger trees is the thinning of the crown, followed by die back of the entire crown, and it progressively worsens until the entire tree is dead. Tree species most suspectitible to short term and long term drought are shallow rooted varities such as maple and birch. This is most noticeable in early or late spring after green out, when the crown does not fully leaf out.
Trees most tolerant to extended drought periods are regional recommended cultivars of these species: Burr Oak, Hackberry, Green Ash, Kentucky Coffee Tree, Honey Locust. These trees are all native to the Great Plains.
Roots of established trees (4 years or more) are out around the tree as far as the tree is tall which equals the diameter of the height of the tree. The roots are located where there is good aeration, they occupy the same zone of soil as the grass roots do.
Plants need good aeration of the soil in order to have proper drainage. Good aeration equals good drainage.
A simple way to check your drainage is to dig a hole 12" deep,and fill it with water. See how long it takes it to drain.It should only take a matter of minutes. If water is still in the hole more than 12 hours later, or days later, you are lacking aeration and/or drainage and the tree will essentially suffocate due to poor aeration.
Symptoms of a tree problem under poor drainage often mimic those due to drought.
If you determine you have a drought problem and not a drainage problem, you need to determine how much you are watering in order to water properly.
If you are a manual irrigator, run your sprinklers, put a container near your sprinkler and at the outer edge of the sprinkler coverage area for one hour, and see how much water is in your containers. The idea is to put enough water on to soak down into the soil around the trees 10-12" once a week. This allows the roots to go deeper than just the first few inches of soil . For automatic lawn sprinkler systems, you will also need to determine how much water is being put down for your trees. 15 minutes cycle rotations twice a day may not be as much water as you think. Put containers under the tree that will give you a good idea of the water coverage under the entire canopy of the tree, not just near the trunk. 1-2" per week is ideal.
Whether the issue is drought or poor drainage, the problem can be solved.
The most economical way to solve poor drainage site problems, is by creating island communities.
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