There are three common ways to fertilize woody plants.
Foliar fertilization, a water soluble fertilizer that is sprayed on the foliage, may help small woody plants, especially plants that aren’t getting enough iron. Be careful not to burn the foliage of plants by applying too much or too strong a fertilizer or by applying when temperatures are too high. At best, the results of foliar fertilization are short lived and it is only marginally beneficial for larger trees.
A granular fertilizer may be spread on the soil underneath a tree or shrub. For established trees, spread the fertilizer 10 to 20 feet past the canopy of the plant. This method is the most effective in a bed without ground cover or grass.
Fertilizer may be applied below the soil surface, at and beyond the drip line, using a root feeder with a fertilizer attachment. Although this method requires the most work, it produces the best results.
For general fertilizing, use a complete fertilizer that has the approximate ratio of three parts nitrogen, one part phosphorus and one part potassium and does not contain herbicides.
For iron deficiencies use a chelated iron fertilizer. Chelates help keep iron from binding to soil particles for a period of time making the iron available for use by the plant.
Fertilize before July or after the leaves have dropped in the fall so the plant is able to harden-off properly for the fall.
Over-fertilizing can severely damage or kill woody plants. Read manufacturer’s instructions on the amount of fertilizer to use before beginning.
For more information, see the following Colorado State University Extension fact sheet(s).
For more information, see the following Planttalk Colorado™ script(s).