Watering instructions for trees and shrubs

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Many trees and shrubs fail to survive transplant shock because they receive too much or too little moisture. This fact sheet offers tips on proper watering techniques.

Water thoroughly before planting, at planting time, and again the following day to thoroughly settle the soil and eliminate large air pockets. Water new trees frequently every other day for the first week or two. Then cut back to twice a week for a month after that, and then every 7-10 days from then on. Figure 1 gallon per inch of tree trunk diameter per day. For example: if you’re watering a 1” tree every other day you need 2 gallons of water. If you are watering every 10 days you will need 10 gallons.

Proper watering throughout the first growing season often means the difference between success and failure. Problems arise when the medium in the root ball accepts and retains moisture differently than surrounding soil. Backfill soil can be thoroughly saturated, while the medium in the root ball is relatively dry.

Retain water around the base of newly planted trees by building a low berm just outside the planting hole. This creates a basin to retain moisture until it soaks into the root ball and adjacent backfill soil.

Note: an alternative to a handheld garden hose is a 5 gallon bucket with one or more small holes (1/8 inch diameter) drilled in the side near the bottom. Simply fill the bucket and let it leak slowly. Bags made specifically to retain and slowly release water are also available. A sprinkler does not provide a deep enough watering for trees and shrubs it really only saturates the top inch or two of soil. Letting the water trickle out from the hose about the size of a pencil for 30-60 min will provide a deeper watering.

After the first month, a weekly soaking to apply approximately 10 gallons of water should be sufficient to support spring-or-summer-planted trees and large shrubs on most sites. On sandy soil, split the 10-gallon application into two 5-gallon applications three to four days apart. Larger B&B or spade-dug trees require more water. Add 10 more gallons per inch of trunk diameter greater than 2 inches (measure 6 inches above the ground).

Smaller trees and shrubs may require less water, but the quantity should be sufficient to thoroughly moisten the entire root ball.

Note: in an effort to get new trees and shrubs off to a good start, it is easy to overreact and water too often. This keeps soil excessively wet and causes a different set of problems. Over watering can cause “wet wilt”, which looks similar to wilt caused by dryness. When soil stays wet for an extended time, root damage can occur due to oxygen depletion. As a result, leaves wilt and do not recover, even if water is added.

In the absence of rainfall, continue watering newly planted deciduous trees and shrubs until their leaves fall. Evergreens should be watered until the soil freezes. but as temperatures cool and days become shorter, plants use less water. In a typical year, watering can be reduced to alternate weeks by mid-August, so they can harden off.

During dry winters with not much snow fall, water evergreens when the ground isn’t frozen and a few days of mild weather are predicted.

Continue regular watering as long as the tree is considered a new transplant. Without rainfall, plants require regular watering until they become established. This may take a couple of years depending on when they were planted. The establishment period for trees extends through the first three growing seasons, and even longer for larger-diameter trees. During the second and third growing seasons after planting, continue to water trees and shrubs every 10 to 14 days if it doesn’t rain and soil moisture indicates a need. As the root system extends and grow outward, water in a wider ring around the plants, soaking the soil to a depth of 8 to 12 inches. One gallon per square foot of soil surface area within and just beyond the root zone.

Grass Competition
Turfgrass growing over the root system of young trees competes for moisture. To reduce competition, maintain a grass-free area around the base of the young tree, extending to the drip line of the outer branches or beyond. An organic mulch around the base of young trees and shrubs is recommended to keep the soil moisture more uniform and to stabilize the soil temperature. Apply and maintain an organic mulch ring 2 to 4 inches deep around the base of the tree, covering the grass-free area. Keep mulch 3-6 inches away from the main trunk of the plant. Mulch in contact with the lower bark can keep bark wet, contributing to canker infection, decay, or girdling.

Water in the early morning. If you water mid-day, much of the water just evaporates. Evening watering should be avoided because it can encourage the growth of mold, fungus, and root rot. If evening is the only time you are able to water do it early enough so it has time to dry out some before nightfall.

Do not fertilize. In general, most trees and shrubs don’t require fertilizing at all, with only a couple of exceptions (azaleas and blue hydrangeas). The roots need to grow and establish themselves first before they can support any more top growth. You can kill the tree with fertilizer. Be patient and just water; but do not over water.