Answer: Like all landscape plants, evergreens remove nutrients from the soil. In the forest, needles and twigs accumulate on the ground and return nutrients to the soil. Under cultivation, evergreens usually receive fewer nutrients from this source because some needle and twig litter is removed beyond the drip line or tips of their branches.
Though evergreens generally require less fertility than deciduous trees, the plant itself will often indicate when it needs fertilizer. If growth rate and needle color are normal for a particular variety, fertilization is not necessary. If new growth is sparse or slow, or the needles are not a healthy color, or are shorter than normal, you should probably fertilize.
A complete fertilizer that supplies nitrogen, phosphorus, and potassium, such as 10-8- 6, is a good choice for evergreens. This formula can vary somewhat, but usually the nitrogen content (the first number) will be higher than the phosphorus (second number) or potassium (final number).
The best time to fertilize is early April, before new growth expands, but you can apply fertilizer anytime until midsummer (roughly July 15). Applications beyond this period will stimulate growth late enough in the season that it may not have time to harden off before cold temperatures arrive. Such growth is much more likely to suffer winter injury and dieback.
Good luck with your conifers!
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