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Trees in Shock

Recently planted trees are in shock. Irrigate them regularly.

Top left: These balled-and-burlapped trees can lose 95 percent of their feeding roots in the transplanting process. They will be in shock for several years. Top right: A common malady is scorching of leaves.Bottom left: Irrigating with perforated 5-gallon pails. Quarter-inch-diameter holes were drilled in the pails to slowly emit water.Bottom right: Irrigating with Gatorbag.Did you plant any trees recently? If yes, we need to give these trees special attention. They are suffering from shock.

When a tree is dug for transplanting, it can lose 95 percent of its root system. Wow! That’s shocking!

How long does it take for a tree to recover? Big trees suffer a long time; small trees suffer a short time.

Tree size is measured by its caliper. For young trees (less than 4 inches in trunk diameter), a tree’s caliper is its trunk diameter at 6 inches above the ground.

There is a rule of thumb that for every inch of caliper, it undergoes shock for 1 to 1.5 years. For example, a tree with a 2-inch caliper will take 2 to 3 years to recover from shock.

How often should I water? For the first two weeks, a new tree can be watered every day if the soil is dry. For the first growing season, it can be watered every 2–3 days when needed. In future years, the tree should be monitored weekly until it’s overcome its shock.

How much water? This varies, depending on the type of soil, weather patterns, and even the tree itself (some trees like it moister than others). Here are some guidelines:

One rule of thumb is a tree requires 10 gallons of water per week for every inch of caliper. If you water about 3 times a week, then a tree would get 3.3 gallons per inch of its caliper during each irrigation.

This amount agrees with the recommendation of Colorado State University (2–4 gallons per inch caliper each irrigation) but exceeds the recommendation of the University of Minnesota (1.0–1.5 gallons per inch caliper each irrigation).

Another rule is to irrigate 5 gallons per week for every square yard of mulch beneath the tree.

These are only guidelines. Before you irrigate a tree, check to see if the soil is moist. Get a shovel or a metal rod and go 8 inches deep. Water only if the soil is dry. We want to keep the soil moist but not soggy.

Overwatering is just as harmful as underwatering. Tree roots need air. Overwatering fills air pockets with water, effectively drowning the roots. The roots will rot and the tree will turn yellow and wilt.

A slow watering is best to make sure the water goes to the tree roots and does not run off. You can water with a soaker hose, garden hose, perforated pails, Gatorbag or drip irrigation (bottom photos).

Established trees generally do not require watering unless there is a drought.

Written by Tom Kalb, Extension Horticulturist, North Dakota State University. Published in the NDSU Yard & Garden Report, July 13, 2016.
Koetter, R. 2008. Seasonal care of trees & shrubs: Watering. MyMinnesotaWoods. University of Minnesota Extension: Twin Cities.
Whiting, D. 2014. Care of recently planted trees. Colorado State University Cooperative Extension: Fort Collins.
Zuzek, K. 2016. Watering newly planted trees and shrubs. University of Minnesota Extension: Twin Cities.
Photos were made available under Creative Commons licenses specified by the photographers: samuel bietenholz; Kelsie Egeland, NDSU; Tom Kalb, NDSU and Angela de Marco.

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