Why are all my leaves falling off my hydrangea as soon as they open?

Question

The leaves all fell off and now the new ones are falling off as soon as they open; they are a light green.

Answer 1

It sounds as though you may have a powdery mildew problem. You may need to apply wettable sulfur fungicide to the plant, but first clean out and remove all dead leaves, and clear any weeds or other detritus around the plant. Once you've treated it, you should surround it with mulch. When it perks up, you may want to fertilize it.

Here are two articles:
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/common-hydrangea-diseases.htm
https://www.gardeningknowhow.com/ornamental/shrubs/hydrangea/fertilizing-hydrangeas.htm