Evergreens, like all plant life, consume nutrients applied to and stored in the soil. In their natural habitat, evergreens are fertilised 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 fertiliser.
Optimal Fertilizer Formulations
Evergreens benefit best from the application of a complete fertiliser formula that includes nitrogen, phosphorus and potassium in a ratio such as 10-8-6. While this blend can vary, use a fertiliser 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 fertiliser to rejuvenate them, young evergreens can be coaxed into more rapid growth with careful applications of fertiliser.
Seasonal Fertilizer Application
Apply fertiliser in the early spring around mid-April and up through mid-July. Laying down fertiliser 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 fertiliser such as Osmocote or Sta-Green. If you apply this type of fertiliser in the late summer through late fall, it may help the evergreens through the stress of winter.
Always apply fertiliser 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 fertiliser 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 fertilised. If your evergreen has its appropriate colour and the needles are lush and not degraded in quality or amount, you may not need fertiliser. The roots of your evergreen could be benefiting from fertiliser applied to soil in adjacent areas. If your evergreen is losing its colour, its needles are dropping and not regenerating--leading to a sparse appearance--or the needles and/or branches seem stunted or malformed, apply fertiliser. 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, fertilise.
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 fertilising. The soil test tells you what is lacking and what is in abundance so that you can create a fertilising program balanced for what the evergreens need.