The “growing” concern for trees this spring is the drought that is intensifying across much of South Dakota. While it was a relatively mild winter for people, the dry fall and winter was tough on trees and most came into spring already under considerable moisture stress. The dry spring has turned the moderate moisture stress to severe for many trees.
There is not much that can be done at this time to help our trees other than water. This is particularly important for new plantings, no matter if they are seedlings planted in windbreak or a tree planted in a yard. There is no precise recipe for how much and how often trees should be watered; it depends on the soil type and rainfall patterns. However, here are a few guidelines for watering during this drought.
Newly Planted Trees
The most critical watering needs are for the trees that will be planted this spring. These trees do not have a well-developed root system and regardless of whether they are planted bare-root, container or balled-and-burlapped, they will require extra attention to watering this spring and summer. A newly planted seedling needs between a pint and quart of water per day while a newly planted ornamental tree, one about 6 to 8 feet tall, needs about 2 to 3 gallons per day. Ideally this quantity of water is applied daily for the first couple of weeks following planting. The root system of these transplants is fairly small and larger quantities of water may flow away from the tree roots before being absorbed. It is also important to water directly next to the stem during this time period so the water is available to the tree, not the surrounding soil or vegetation.
Established trees do not need daily watering but will still benefit from weekly watering if the rains continue to hold off. A small windbreak tree, one planted a year or two ago, still needs about 2 or 3 gallons of water a week. A 2-inch diameter tree (measured at 6-inches above the ground) should receive about 20 gallons of water a week during drought periods. The best means of applying this water for landscape trees is slowly with a soaker hose placed near the tree. While tree roots typically extend out as far as the tree is tall, the critical watering zone is a distance out about 2/3’s the height. As an example, if the tree is about 12 feet tall, the watering should be done within 9 feet of the trunk.
The water should be placed on the soil, not the foliage. There is a common myth that evergreens absorb most of their water through the foliage. There is no truth to this as the root system is the primary means of absorbing water, the amount of water absorbed into the foliage is insignificant. While there is nothing harmful about watering foliage, it does not result in scalding, it is a waste of the resource.
If the rains begin to fall across the state, supplemental watering may no longer be needed. Trees generally need about an inch of water a week during the growing season. Watering trees during weeks of receiving an inch or more of rain may contribute to root decline due to the lack of soil oxygen.