By Nathan Winter
Extension Educator, McLeod and Meeker Counties
Trees have been under stress again in 2012. Above average heat and summer drought conditions have provided a less than ideal situation. Following is some helpful information for newly planted trees, existing trees, mechanical equipment protection, fertilization, and pruning.
According to the University of Minnesota Forest Resource Extension, in the Midwest region, bareroot trees and shrubs should be planted when the plants are dormant in the spring or at the end of the growing season (fall). Balled and burlapped, containerized, and container grown plants can be planted throughout the growing season, but with caution during the summer months. If planting in the fall, the recommendation is to plant four weeks before the soil temperature drops below 40 degrees Fahrenheit. To plant trees correctly, get a copy of the U of M publication called "Planting Trees and Shrubs in Minnesota", which can be found on the U of M Extension Website: http://z.umn.edu/98n or by calling most U of M Extension Offices. The publication also has choices for proper Minnesota tree species.
Watering is going to be important to a newly planted tree as well as any existing trees on your landscape. Since watering is such a time consuming task, you may have to pick and choose the existing trees that you want to water. I recommend watering any newly planted trees and also water any trees that have shown stress, disease, or insect problems through the growing season. The dry conditions in late-summer and fall in 2012 are going to be very problematic for trees in 2012. Be sure to get out and water trees until the ground freezes.
Water newly planted and existing trees over the root zone of the tree. Roots of trees can vary from 1.5 to 3 times as wide as the canopy. Avoid frequent light watering and instead water infrequently and heavy. You will want to wet the soil to a 6 - 8 inch depth and then let the soil dry out in between. Use a rod to determine when you have wetted the soil to that depth. Believe it or not, you can over water trees, which will starve the roots of oxygen and cause roots to rot. If fall rains are averaging one inch every week, watering will probably not be necessary. Generally, you want to have an adequate amount of moisture before the ground freezes up in late fall, especially with coniferous trees. My Minnesota Woods Website has additional information on seasonal watering of trees and shrubs: http://z.umn.edu/98m.
Protect stems of landscape and shrub trees from animals and mechanical equipment. This is most important on new or young shrubs and trees. Use a mesh or hardwire cloth at least three inches from the stem. Plastic guards can also be used, but they are only recommended to encase the lower part of the stem, where damage can take place. Sun scald can be prevented by wrapping the trunk with a commercial tree wrap, plastic tree guards, or any other light-colored material. Put the wrap on in the fall and remove it in the spring after the last frost. Wraps should be used primarily on new trees.
Fertilizing trees should be done on a case by case basis. A soil test can be done to determine if the soil does not have the adequate amounts of fertilizer in the soil. University of Minnesota Soil Test Kits can be picked up at most University of Minnesota Extension Offices. Often, the tree has sufficient amounts of nutrients available if the lawn is being fertilized regularly. If fertilizer is needed, a late fall application can be done before the ground freezes for coniferous trees and an application can be applied to deciduous trees between when it is fully leafed out and when it will start showing fall color change.
Pruning can also be done this time of year on many trees. Late fall brings the time when it is safe to prune oaks and elms until next spring. During the dormant season serious disease problems are less problematic. Hold off on apple trees until the best window for preventing disease spread, which is late winter (late-February to early-March). Another helpful publication is the University of Minnesota Publication "Pruning Trees and Shrubs" located on the University of Minnesota Extension Website or by calling most University of Minnesota Extension Offices. This publication is a good how to guideline for pruning trees.