"Evergreen plants" are the pines, spruces and other conifers that fill the air with their refreshing fragrance. They are also the broadleaf evergreens--including rhododendrons, azaleas, hollies and boxwoods--that sometimes grace gardens with brilliant blooms and always grace them with attractive foliage. All evergreens require feeding to keep them healthy. Your evergreens' individual circumstances will determine the amounts and types of plant foods or fertilizers they need.
How Often to Feed Needled Evergreens
Needled evergreen trees are lighter feeders than deciduous trees, says Michigan State University horticulture Associate professor Dr. Bert Cregg. They keep the same needles for between 3 and 6 years, while deciduous trees must replace their foliage every spring. One sign that your needled evergreens would like a meal is generalized needle discoloration. Yellow needles mean the plants are short are nitrogen or iron, while purple ones indicate a lack of phosphorus.
How Often to Feed Broadleaf Evergreens
Yearly feeding with a food formulated to increase soil acidity is best for broadleaf evergreens, according to Ohio State University Extension educators Staut and Martin.
When to Feed Your Needled Evergreens
Fertilizer applications on needled evergreens are most effective in early spring, before the trees' needle buds open, although you can feed them as late as mid-July. Feeding any later encourages new growth without giving it enough time to harden before winter, cautions Deborah Brown, University of Minnesota horticulturist.
When to Feed Broadleaf Evergreens
Feed broadleaf plants no later than the first week of June. Like conifers, broadleaf evergreens fertilized after the recommended period may have new foliage killed in a hard freeze.
What to Feed Needled Evergreens
Feed your needled evergreens a complete food with a nitrogen (N) number higher than its phosphorus (P) or potassium (K) numbers. The fertilizer's label prominently displays the three numbers--separated by hyphens--in N-P-K order. Base the amount of food your conifer needs on the number of square feet it covers, measured at its widest spread. For example, a 15-foot wide tree covers 225 square feet (15 times 15). The label indicates how many pounds of fertilizer to apply per 1000 square feet.
What to Feed Broadleaf Evergreens
Foods containing nitrogen as nitrate are unsuitable for broadleaf evergreens. Organic cottonseed meal will acidify the soil, as will many good commercial fertilizers with urea or ammonium-based nitrogen. Adding phosphorus to phosphorus-deficient soils when you fertilize your broadleafs encourages healthy bud formations. Staut and Martin advise using a super or triple superphosphate.
If your needled evergreens are growing in exceptionally poor soil, a late summer or early fall application of slow-release fertilizer is acceptable. It may help them through the winter, says Brown.