Jean Kuehn, UM Extension Master Gardener in Anoka County, February, 2016
In the winter landscape, evergreens add green to the white. Let’s keep them healthy. Evergreens in the woods get nutrients from the twigs, leaves and other natural debris that compost into the soil. In our home landscapes, we tend to tidy up the yards and rake away the morsels that would add nutrients to the soil naturally. While evergreens generally need less fertilizing than deciduous trees, they benefit from some.
Just fertilizing the lawn may be enough. How can you tell? Look at the tree! How is the color? The new needles? Does the tree seem to be growing at a reasonable rate? Does it look healthy?
If it is a newly transplanted tree, be patient. It is normal for any transplanted tree to need time to recover and adjust to the new environment. Smaller trees generally adjust faster than a larger transplant. Keep any transplant well water and do not be too anxious to fertilize until it has settled in to the new location.
If you have less than ideal soil, very sandy or heavy clay, regularly fertilizing can overcome some problems and produce a strong healthy tree. In the sandy soils of Anoka County, heavy rains can wash the nutrients quickly through the soil, leaving the trees without the nutrients they need. These must be replaced.
Ideally, a soil test should be done before fertilizing. Complete fertilizers are labeled with three numbers, for example 10-8-6, for their nitrogen, phosphorus and potassium amounts. The soil test will probably show sufficient phosphorus. If you can’t match both the nitrogen and potassium you need in a commercial fertilizer, just match the nitrogen. The soil test will also indicate if the soil is acid or alkaline. Evergreens grow best in acid soils and some nutrients may be unavailable to the tree if the soil is too alkaline.
Early spring, April, is the best time to fertilize, before new growth begins. Fertilizer can be applied until mid-July, but any later may cause late growth that would be damaged by frost. A slow release fertilizer can be applied even into early fall, and may help the tree without risk of winter injury. Never fertilize any plant that is stressed, from drought or disease. Water trees until you bring the hoses in for next winter.
Mulching is a great way to keep the soil moist under evergreens and minimize the needed water. Do not mound the mulch against the trunk. Three or four inches evenly spread will be fine. You can fertilize right over the mulch. Just water well and enjoy your lovely evergreens for years to come.