This weekend is the best time to fertilize stone fruit and apples to get them ready for the next season. I would recommend a bloom boosting fertilizer like 0-10-X with a predominant phosphorus load or ask your local nursery what they would recommend for your area and soil conditions. This early spring fertilizer will have a chance to break down and will get carried with the spring melt into the roots giving the tree what it needs when it breaks dormancy.
For those who do not have their fertilizer numbers memorized the first number represents Nitrogen content. The zero in the first part of this number 0-10-X indicates that there is little to no traceable Nitrogen. This is good in the spring as Nitrogen will boost tree growth and leafing. You want blooms so the middle number (Phosphorus) is the number that you want to pay attention to for this application. The final number is Potassium. Potassium is essential for the metabolic function of the tree regulating dozens of tree functions and so this number can be as high or even higher then the Phosphorus rating.
Wood ashes are a good spring fertilizer for trees containing mostly Phosphorus and Potassium but it will also alkalize the soil so excessive application can cause problems if used later than the las spring rain as rain tends to be a little acidic and will correct for the alkali of the wood ash.
If there is still snow on the ground this is actually a good thing as it will begin to dissolve the granules and any further freeze cycles will break apart minerals and aid in absorption.
Apply the fertilizer around the drip line and use about a half a pound of fertilizer for a small tree up to 3 pounds for a large tree. In my estimation it is best to guess on the low side as you do not want to burn the roots.
ATTENTION: KEEP FERTILIZER AT LEAST A FOOT AWAY FROM THE TRUNK OF THE TREE TO KEEP THE TREE FROM BURNING.