Answer: It is less wasteful to apply the water directly to the root area when you are trying to keep the soil evenly moist, as you would with a newly planted tree. A soaker hose or drip irrigation system would be the most efficient tool for this. Spruces are however sometimes attacked by mites and these can sometimes be prevented by a weekly washing of the foliage with water from the garden hose -- especially during dry spells. That is the only reason I can think of to water overhead.
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