Don’t guess when it comes to watering a new tree! Until it’s established (in about two growing seasons) figure that a small tree, with a trunk 1 or 2 inches in diameter, needs 10 gallons of water per week.
Here’s a simple way to accurately apply this amount: Drill a 1⁄8-inch hole in the side of a 5-gallon bucket near the bottom edge, just like you see here. Place the bucket at the base of the tree and fill it up — water will slowly flow out into the tree’s root ball, right where it’s needed. Repeat on the other side of the tree and you’ve delivered 10 gallons of water.
Larger trees need more, usually another 10 gallons per inch of trunk diameter. Hot or windy conditions will dry out newly planted trees quickly, so an extra bucket or two may be necessary. In the winter, water once or twice per month, but only if the temperature is above 40 degrees F.