Though different species, apple and cherry fruit trees have similar requirements for water. They require evenly moist soil at all times but can suffocate when the roots are left in standing water. Watering requirements vary by climate zone, soil make-up, tree size and age, season and natural rainfall or lack thereof. Adjusting the proper watering amounts for your trees and location can be done by touch testing the soil and using a baseline water amount and adjusting it up or down for your current local conditions.
Provide young apple and cherry trees under three years of age and taking up less than 5 square feet in soil area with roughly 5 gallons of water per week. Apply in one deep watering session or in multiple sessions or over an extended period with drip irrigation.
Irrigate mature apple and cherry trees that are six years of age and take in roughly 8-square feet of soil with their root mass with 31 gallons of water per week. Larger and older trees with more elaborate root systems may require a bit more water but that should be determined by touch testing until a sufficient watering regimen can be identified and a irrigation schedule established.
Feel the soil with your hands, a few inches down and then up to 1 foot down, periodically to ensure that the soil is moist. Familiarize yourself with the rate of absorption and percolation of water through the soil and the rate of evaporation of water from the surface of the soil. Adjust the amount of water applied and the frequency of irrigation to ensure evenly moist but not wet soil at all times.