Soil moisture is especially important during the first three years following tree transplanting. Below are general rules of thumb to offer the best opportunity for your tree to establish:
Newly planted trees should be well watered about 1-2 times a week for the first few seasons, until the roots establish. Watering new trees can be significantly reduced after a few years, but supplement during periods of abnormally dry weather.
The rate at which the tree is watered is also important. Longer and deeper watering, one that mimics natural rainfall, is always the best approach.
For Small Trees – About 5 gallons of water will soak the entire well of a small tree, or about 1-2 minutes from a garden hose at a slow-medium flow.
For Larger Trees – Watering should be moved away from the trunk and out to areas around the drip line.
Water deeply rather than frequently. Because most tree roots are found in the upper 18 – 24 inches of the soil, this is the zone that should be wetted up in each irrigation cycle. Each deep irrigation will meet a tree’s water needs for between 10 days to 4 weeks during the hottest part of the summer, depending on the tree species and soil type.
Stop watering when runoff starts. Soils high in clay accept water slowly, often as little as 1/4 inch per hour. Water infiltration is especially slow in compacted soils. If water starts to pool or run off, stop irrigating, let the water soak in, and start watering again.
Don’t saturate the soil for long periods. Water displaces air in the soil, so long periods of soil saturation can suffocate growing roots. Take a long enough break between irrigation cycles to allow the free water to be absorbed. If in doubt, probe or dig to make sure that the soil isn’t soggy below the surface.