Three months ago I planted an Afgan Pine (Pinus elderica), Juniper (Junipcrus chinensis), Navel Orange (Citrus sinensis), and a Thuja Green Giant Arborvitae, all between 3 and 4 feet tall. Using a moisture meter, wooden dowel or my finger, I recently noticed that starting about 12" away from the trunk, the closer you get to the trunk, the drier the soil becomes. Is that because the root ball dries out quicker then the surrounding soil and if so should I water when the soil about 6" away from the trunk is 'low moist'? I use a 1/2" soaker hose wrapped twice around the trunk at about 6" from the trunk. The soaker hose dripping for two hours dispenses between 18 and 24 gallons depending on which tree I am watering. Generally I water every 3 to 4 days now because in southeast Arizona the temperature reaches 100 t0 105 F during the afternoon. All trees are in well draining soil and have 3" of compost mulch.