Answer: Hydrangeas will grow in full sun to partial shade, but not full shade. Hydrangeas grow best in rich soil, high in organic matter, that never dries out but also has good drainage. To achieve a beautiful blue color, your soil has to be on the acidic side (acidic soil produces blue hydrangea blooms, alkaline soil produces pink blooms, if the soil is very, very acidic, they will be white). To find out your soil's acidity level, you would need to have a soil test performed. Contact your local county extension office for details. Your soil report would also have advice on how to make any needed amendments to the soil.
If the plants are getting the sunshine they need, I think the problems are soil related. Your plants should be pruned after they've finished flowering. Hydrangeas bloom on new shoots produced on last year's stems. If you prune now, you'll prune off next season's bloom. Wait until after they've bloomed to get them back into shape.
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