Although there are different ways to fertilize spruce trees, This Old House recommends using a slow-release fertilizer. You will also need a small auger or an iron bar to make holes around the tree.Continue Reading
Before you fertilize a tree, you need to find its drip line. This is where rain water drips from the outermost canopy of the tree. You will fertilize from this line and out.
Using a small auger, or even an iron bar, dig small holes 12 to 18 inches deep around the drip line of the tree. Make these holes 8 to 12 inches apart.
Use a slow-release fertilizer and mix it with sand, compost, dirt or a combination of these. Talk to your local cooperative extension to find out what fertilizer mix is best for your area.
Take the fertilizer mix and fill the holes around the drip line of the tree. Do this once a year, preferably in the fall, to keep your trees healthy.