Answer: Bigleaf hydrangeas bloom on wood that grew the previous year. The most common reasons for lack of bloom are excessive winter damage and pruning at the wrong time. If the plant dies back substantially in the winter to the point that you are removing entire dead branches in the spring, then you will be forced to remove flowering wood. (The only "safe" time to prune is right after flowering. If you suspect winter damage, wait until late spring before removing any branches that seem dead -- be certain they are truly dead before you trim them off.) If you suspect winter damage, try providing a wind break in winter to shelter the plants and consider wrapping them for winter. In addition, oscillating spring temperatures and late frosts can sometimes damage buds as they begin to swell and open. Another reason for lack of bloom can be insufficient sunlight. These plants are somewhat shade tolerant and in fact resent afternoon sun, but they do need some direct morning sun or bright dappled light all day in order to bloom. They also need evenly moist soil and overall general good health. Since your plants seem to be growing, I don't think that would be the problem.
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