TREE WATERING GUIDELINES AFTER PLANTING How much and how often to water. It is important to be diligent about regular watering, especially in the first year. Here are some tips. Water your tree 5 gallons every 3 - 4 days, or a total of 10-15 gallons weekly. Because this is only a rule of thumb, it will need to be adjusted to your unique site. To do this, check the soil moisture a few inches below the soil surface of the root ball. If the soil is very dry or leaves look wilt