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In choosing an evergreen fertilizer, seek out one that provides complete nutrition by supplying nitrogen, phosphorous and potassium. A formulation such as 10-8-6 — meaning the evergreen fertilizer contains 10 percent nitrogen, 8 percent phosphorous and 6 percent potassium — is often suggested by professional gardeners. Soil tests will identify what, if any, of these elements are in short supply in the soil. Evergreens tend to need less fertilization than deciduous trees and shrubs, although if growth is slow or the needles are shorter than normal and are not a healthy color, applying an evergreen fertilizer will usually remedy the situation.
Evergreens that grow naturally in the forest derive much of their nutrition from the needle and leaf litter that covers the forest floor. In gardens, that nutrition source is often removed by the gardener, necessitating the use of an evergreen fertilizer. Regular fertilizing might be needed if your evergreens are growing in a less-than-ideal site. If the soil is very sandy or has a high clay content, fertilization might help. Some gardeners also apply fertilizers to very young evergreens to encourage faster growth.
Fertilizer spikes are an easy way to feed evergreens, but because each spike contains relatively little fertilizer, it might take a considerable number to feed your trees, making this a less cost-effective solution. A liquid evergreen fertilizer used with a root feeder can also be effective when the soil is well drained and does not contain much clay. Liquids might not work well in very sandy soils, because the fertilizer might leach through the soil too quickly to benefit the trees. As with spikes, liquids might not be the most cost-effective solution.
Evergreen fertilizers are produced from both organic and non-organic sources. After running a soil test to determine what specific nutrients are needed, you can look on the Internet to find many sources of information about available fertilizers, their sources and their formulations. Another good source of advice are agricultural extension agents who are familiar with the specific needs of evergreens in your area.
Although evergreens might benefit from fertilizers applied to adjacent lawns, applying fertilizers using a drop spreader in a manner that makes them more readily available to the trees' root systems will optimize the fertilizers' effect. Granular fertilizers are relatively easy to apply on the surface, but if they contain a high proportion of nitrogen, they might burn surrounding grass and other plants. A more effective way to reach the evergreen's roots and eliminate burning of other plants is to place the fertilizer in holes that are 8-12 inches (20.3-30.5 cm) deep. The holes should be spaced about 2 feet (61 cm) apart in concentric circles beginning about 18 inches (45.7 cm) from the trunk in the case of younger, smaller trees. When fertilizing larger, mature trees, begin the holes about 3 feet (91.4 cm) from the trunk.