when do I fertilize hydrangeas?

Question

I live in Massachusetts in zone 7

Answer 1

One can use organic additions to the soil, such as manure and compost, or chemical fertilizers.

If fertilizers are used, apply a slow release, balanced fertilizer once in June for more Northern areas. (For the south, apply fertilizer in May & again in July.)

The amount of fertilizer used per plant will vary with the size of the plant. It is much, much better to err on the side of too little fertilizer than too much. A very small plant will take about 1/4 cup. A very large shrub will take 1 - 2 cups spread around the drip line of the branches (not next to the trunk).

Never fertilize a plant that looks sick or wilted. If a plant is struggling due to a disease or root problems, the fertilizer will only add stress to it. Try to cure the illness before adding fertilizer.
http://www.hydrangeashydrangeas.com/planting_fert.html