I have trees, maple, pine, and fruit trees in very rocky, mainly granitic soil. We are located in the part of Lyon County, Nevada that is on the very dry side of the Virginia Range. What type of fertilizer should I use and when should it be applied?
Probably the best nutrient source you can give to your trees would be organic matter in the form of compost, worms casting or well aged manure that has had the salts leached out. In Nevada we are lacking in organic matter and that is what the micro organisms feed on to help feed out tree and plants. By adding compost as a topping mulch you are helping feed the soil which will then feed the plant. There are several other benefits like moisture retention, more consistent soil temperatures, weed suppression and the fact you can add it at any time of the year, plus you don't need a soil test. Many time before recommending specific fertilizers it is nice to have a soil test done to tell you if you are in excess or low in any nutrients. For your area an all-purpose 10-10-10 would be fine to use in spring on most of your plants, but I would only recommend the compost for your fruit trees. Many times people over fertilize fruit trees and limit the amount of fruit that can be produced. https://www.unce.unr.edu/publications/files/nr/2009/fs0914.pdf https://www.unce.unr.edu/publications/files/ho/2014/fs1414.pdf https://www.unce.unr.edu/publications/files/nr/2009/fs0916.pdf