The answer depends in large part on the age and size of your apple tree. If it’s an established tree and you’re concerned with watering it during times of heat and dry conditions, you should at least water thoroughly beneath the canopy (as far as the branches reach).
If the tree is young and not yet well-established, watering closer to the trunk makes more sense, particularly if you created a “saucer” at its base when you planted the tree, to trap moisture. This is especially important on a slope, not only to make watering the tree easier but to take full advantage of rainfall.
If you didn’t make that saucer when you planted, you can still build up the soil where it slopes away from the tree. Just be careful not to add additional soil over the root ball closer to the trunk. (Think of the tree as the center of a 3-foot-wide saucer.) Top with a few inches of wood chip mulch to help the soil retain moisture, but keep the mulch a couple inches away from the trunk.
Hose trickling slowly
If the tree has only been in your landscape for a year or two, you should let a hose trickle slowly into the saucer two or three times a week, depending on temperature and natural rainfall. Poke a wooden dowel about 8 inches into the soil to see if it’s fairly dry. If so, run the hose for several hours to give the roots a good soaking.
Frequent, shallow watering is not good for the developing roots; instead water deeply less often. As the tree grows and its roots spread farther, you won’t have to supply additional water except during periods of extreme heat or drought.
Deb Brown is professor emeritus, University of Minnesota Department of Horticultural Science.