Newly transplanted/planted trees need at least 10 gallons of water per week. The secret is getting that water to soak deeply into the soil, so it evaporates more slowly and is available longer to the tree’s roots. One way to do this is to punch a small hole in the side of a 5-gallon bucket and fill it with water. Let the water dribble out slowly next to the tree. Refill the bucket once, and you have applied 10 gallons. Very large transplanted trees and trees that were transplanted 2 to 3 years ago will require more water. A perforated soaker hose is a great way to water larger trees, a newly established bed or a foundation planting. In sun-baked soil, you may need to rough up the surface with a hoe or tiller to get the water to infiltrate easily. It may be helpful to set the kitchen oven timer, so you remember to move the hose or shut off the faucet. If you are seeing surface runoff, reduce the flow, or build a berm with at least a 4-foot diameter around the base of small trees to allow the water to percolate down through the soil, instead of spreading out.