Extension Forest Entomologist Successful Christmas tree growers apply herbicides, insecticides and fertilizers as needed for optimum tree growth. Fertilization Tree-growing operations use fertilizers to increase growth, and to improve the trees' vigor, color and needle density. If any of these factors is not adequate, or if trees are spindly and off-green, fertilization is needed. Most New Mexico soils do not con tain enough nitrogen, and adding this element usually corrects the problem.
Studies show fertilizer applied to new plantings can burn tree roots and cause other injury.
Fertilization should begin the second year after planting, and should be done in spring before buds begin to swell. Spread 3 to 4 heaping tablespoons of ammonium sulfate per tree in early spring. Scatter the fertilizer evenly under the drip line, but never in direct contact with the tree's root system. Be careful not to concentrate large amounts of fertilizer near the stem. Split the application in sandy soils, applying half in spring and the other half in late June.