I keep getting calls asking: "what's up with the trees?" They are slow to leaf out, full of seeds, and the leaves are relatively small and more yellow than normal. All of these can be symptoms of drought stress. According to the Minnesota Climatology Office, we are in a "long term episode of dryness" that started in June of 2008. Although Douglas County is not identified as a severe drought area, we are abnormally dry for the season. This lack of water has definitely affected many of our trees.
What are some of the symptoms of drought stress in trees? Look for any of the following signs:
Leaves lighter in color and smaller than normal.
Tree canopy may be thin.
Suckers develop on branches and trunk.
Heavy seed production.
Stems and twigs die, with the outermost and upper ones dying first.
Evergreen needles brown, yellow, red or red-purple from the tip downward.
Leaves roll up and/or are misshapen.
Leaves drop prematurely.
These symptoms can also be indications of other stressors including insect damage and disease. Because drought stressed trees are in a weakened state, they are susceptible to these other stressors, so treatment might require more than deep watering. Trees absorb water through the top 6-12 inches of roots, which requires about 10 gallons of water per inch of trunk diameter per week. Try one of these effective watering methods the next time you water:
1. Wind a soaker hose around your tree at two foot intervals extending to the drip line. (The drip line is an invisible circle around a tree directly under the tips of its outermost branches.)
2. Set your garden hose on a slow trickle and rotate it around the drip line.
3. Drill small holes in five gallon buckets and set them around the drip line until the desired quantity of water is evenly distributed around your tree.
Whatever method you choose, remember to water deeply once a week. Watering more frequently for short periods of time encourages shallow root development, which can lead to further drought damage.
Do not fertilize a tree that is under drought stress. Salts in fertilizers may burn roots when there is not sufficient water. Fertilizers may also stimulate top growth, resulting in too much leaf area on the plant for the root system to maintain during dry periods. Retain soil moisture by mulching around your trees with 4 inches of organic mulch. Use wood chips, shredded bark, leaves or evergreen needles as mulch - avoid the use of stone or rock near trees as this increases air temperatures and moisture loss from leaves and stems. Be sure to pull back mulch 6" from the trunk of the tree to discourage mold growth, and insect and small mammal damage.
Care for your trees until the ground freezes. Well maintained trees have a much better chance of surviving our harsh winters, and will have a better start the following spring.
Until next time, happy gardening!