Watering Trees During Drought

Standish_Park_Tulip_Tree
 
Wondering why the trees in your yard or around town are dropping leaves or have any other symptoms that something is wrong with the tree? If so, there is a pretty good chance it is the lack of rain this year. Dry soil conditions can significantly reduce the life span of valuable landscape trees. Because they are difficult and expensive to replace, trees need attention during and after periods of drought.
 
Symptoms:
  • wilted foliage
  • sparse canopy of off-color and undersized leaves
  • leaf scorch
  • yellowing
  • leaf drop
  • premature fall coloration
Closer inspection will reveal limited twig growth and small, poorly formed buds. Growth for several seasons may be stunted even if there is sufficient rainfall.
 
Perhaps more life-threatening than anything to a tree suffering from drought, is invasion by borers and disease-causing organisms that can happen as the tree is recuperating and still in a weakened state. For instance, elms succumb more quickly to Dutch elm disease and white-barked birches are more susceptible to bronze birch borer during drought.
 

Water Appropriately

Since most of a tree’s active roots are within the top 12 inches of soil, a good way to water is to put a sprinkler beneath the tree. Place a coffee or soup can close by and run the sprinkler slowly until 2 inches of water has collected in the can. Be sure to water the entire root zone beneath the tree canopy. The best time to water is typically in the morning.
 
Slow, deep watering every five to seven days during drought is ideal for mature trees in the Midwest and every four to six days during drought for mature trees in areas with 95 to 105 degree temperatures (Fahrenheit). In hotter regions, reduce watering frequency as temperatures cool to 75 to 85 degrees. When watering, remember that a tree’s root zone may extend well beyond the tree canopy if there is ample space available.
 
For young or newly planted trees, slow, deep watering every two to three days is a good gauge. There are also a number of "soaker products" available to keep newly planted trees from drying out.
If turf is underneath the canopy of the tree (whether young or mature), more water will be needed because the turf will absorb much of the water that is applied to the surface. The goal is to get the water through the turf roots and down to the tree roots. Removing the turf around the base of the tree and replacing it with mulch can help eliminate competition for water between the turf and the tree.
 

Soil Moisture Check

When watering any tree, remember that the soil type and method of water delivery have a big impact on how successful the general recommendations might be. Trees planted on a slope may need some type of soaker hose or drip emitter, as applied water will run-off. Sandy soils need shorter watering intervals, and clay soils should have longer intervals. Clay soils are hard to wet, and water will not infiltrate, but puddle, if applied too quickly. The puddling of water may make one think sufficient water has been applied, but often only the top inch may be wet. The depth to which water has infiltrated the soil must be checked by hand.
 

Proper Tree Care

Proper tree care during drought includes watering, mulching, and pest management. Organic mulch, such as wood chips, to a depth of 2 inches, will help the soil retain moisture. If the soil does not have any moisture, the mulch will have little effect; as there is no water to lose. Inorganic mulch, like crushed granite, also helps the soil retain moisture, but it may not be as effective as organic mulch.
 
Routine pruning is not recommended during severe drought, as this can cause tree’s stress, which can make the trees even more prone to borer attack. Pruning may still need to occur for building clearance, and utility lines. Fertilization with a slow release fertilizer can be done, but will be of little benefit during severe drought, as water is necessary to make nutrients available. Fast release fertilizers like urea should be avoided, as they will utilize water first and make the effects of drought more severe. Planting or transplanting trees are usually not recommended during drought conditions. 
 
For more information, contact Ryan Creek, City Arborist, at 309/345-3621
 

 

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