Evergreens, like all plant life, consume nutrients applied to and stored in the soil. In their natural habitat, evergreens are fertilized by leaves, needles and fruits that fall to the ground and decompose into a natural compost. When grown in the garden or under cultivation such as in a nursery setting, evergreens do not have the benefit of these nutrients as most debris is cleaned away to maintain a tidy appearance. Evergreens in these settings benefit from carefully applied fertilizer.
Optimal Fertilizer Formulations
Evergreens benefit best from the application of a complete fertilizer formula that includes nitrogen, phosphorus and potassium in a ratio such as 10-8-6. While this blend can vary, use a fertilizer in which the nitrogen--which is always the first number in a three-part formulation--is higher than the phosphorus or potassium numbers, the other two numbers respectively. In addition to mature evergreens benefiting from fertilizer to rejuvenate them, young evergreens can be coaxed into more rapid growth with careful applications of fertilizer.
Seasonal Fertilizer Application
Apply fertilizer in the early spring around mid-April and up through mid-July. Laying down fertilizer later than this forces new growth that may not have the time to harden off and survive the winter. The one exception to this timing is if you use a slow-release fertilizer such as Osmocote or Sta-Green. If you apply this type of fertilizer in the late summer through late fall, it may help the evergreens through the stress of winter.
Always apply fertilizer to evergreens that are not dried out at all and to soil that is uniformly moist. If your evergreens are drought stressed, water well for a week or so before applying fertilizer and continue regular watering to reduce the chance of root burn or foliage dieback.
Knowing If Your Evergreen Needs Fertilizer
Your evergreen gives clues about when and how it should be fertilized. If your evergreen has its appropriate color and the needles are lush and not degraded in quality or amount, you may not need fertilizer. The roots of your evergreen could be benefiting from fertilizer applied to soil in adjacent areas. If your evergreen is losing its color, its needles are dropping and not regenerating--leading to a sparse appearance--or the needles and/or branches seem stunted or malformed, apply fertilizer. If you are growing evergreens on the edge of their appropriate environmental requirements such as in a clay soil, or if disease or insects have taken a toll on the plant, fertilize.
If you are in any doubt about the quality or nutrient value of your soil, get a soil test done before making amendments to the soil or fertilizing. The soil test tells you what is lacking and what is in abundance so that you can create a fertilizing program balanced for what the evergreens need.