Hundreds of thousands of trees are planted along city streets and other public, commercial and private properties in the United States each year. Unfortunately, perhaps 50% or more do not survive beyond one or two years……….Why?
When a tree is dug for transplanting at a nursery, up to 90% of the tree’s root system is severed and left behind. This results in a very stressful condition for the tree called “transplant shock”. Transplant shock results in increased vulnerability to disease, insects, and most of all, moisture stress. Water is the lifeblood of the tree. The nutrients it carries are crucial to carry on photosynthesis, which in turn produces critical carbohydrates necessary to re-grow roots lost during transplanting. The newly planted tree must get 100% of its’ water needs from the remaining ten to twenty percent of the original root system. The water in the soil ball containing these roots is heavily “mined” for water during the re-establishment stage. It can dry out long before the surrounding soil does. ROUTINE REGULAR WATERING IS ABSOLUTELY CRITICAL FOR SURVIVAL OF THE NEWLY PLANTED TREE. This is true even if adjacent established trees appear to be doing fine.
Research across the country has consistently shown that trees need to be watered with careful irrigation for a time period of one year for every inch of trunk caliper measured at six inches above the soil grade, in order to re-grow the lost root systems. ………How much water, and how often?
A rule of thumb for field grown trees is 5 gallons of water per inch of trunk caliper. Trees should be watered within 4 to 6 hours of planting, and thereafter watered weekly unless the tree has received 1 inch or more of precipitation that week. Watering amounts may be reduced or even skipped that week depending on the amount of rain that has fallen. Be aware that a larger tree such as a 4 inch caliper will need careful monitoring of the above application criteria for a sum of years corresponding to each inch of caliper. A larger newly planted tree of 6 inch caliper for example can be lost in the sixth year after planting if water needs are not addressed in a precipitation deficient year.
A final important note: Mulch……a mandatory 2 to 3 inch mulch layer will greatly benefit the speedy establishment of newly planted trees by retaining moisture and keeping the immediate root zone area cooler during the hot days of summer. Likewise, it also has benefits during the winter by delaying the onset and severity of freezing temperatures in the root zone. This will allow longer root growth into the late fall, and likely earlier root growth start up in the spring.
Harold Hoover, Board Certified Master Arborist, Kramer Tree Specialists, Inc.