Arizona's Best Tree & Shrub Food with a N, P and K of 13-7-7 is a formula of nutrients which support sturdy growth of trees, shrubs and evergreens. Added sulfur helps plants to withstand weather extremes and improves overall color. Most trees and shrubs benefit from a feeding three to four times a year during the growing season. Make the first feeding in early Spring just before new growth starts, the second and third feeding should be made in the middle and late Spring, at six to eight week intervals and the fourth feeding in September.