By Dr. James Klett, Dept. of Horticulture and Landscape Architecture, Colorado State University
If trees are to survive, the gardener needs to understand the basics of watering. Incorrect watering can cause more harm than good.
Overwatering, very common with newly transplanted trees, forces oxygen out of the soil around the roots and can lead to death of a tree. A good indication of too much water is yellowing of the foliage that develops first on the inside leaves and progresses to outer leaves.
This leads to the question--when and to what extent should I water? It is important to determine moisture levels of the soil in the root zone. Most roots in Colorado's claylike soils are 6 to 10 inches below the soil surface. It is easy to determine soil moisture by carefully digging down 6 to 10 inches. If soils feels powdery or it crumbles, it is time to water. If it clings together when squeezed, it contains adequate moisture.
To water a newly transplanted tree, you might want to use a soil needle or root feeder attachment to a garden hose. This allows some water movement directly to the root zone. Insert the soil needle in a zigzag pattern around the root ball of the transplanted tree. This ensures that all new feeder roots outside the original root ball receive adequate water.
Water newly transplanted trees thoroughly to late August, than gradually cut back on water to allow for "hardening off" before cold weather sets in. After the leaves have dropped off, continue watering if natural moisture is inadequate.
To help reduce moisture loss, mulch around newly transplanted trees. These watering techniques will help maintain a high survival percentage to your newly transplanted trees.