Answer: The typical bigleafed hydrangeas should not be cut back in the fall. The reason for this is that they bloom on old wood, meaning the stems from the year before. Pruning should be limited to immediately after they bloom, and is usually only done to thin out a few of the oldest stems by cutting them off at the base.
General care includes applying compost and/or a complete fertilizer according to the label instructions each spring, providing water if needed during dry spells to keep the soil evenly moist but not soggy, and maintaining several inches of organic mulch over the root zone (but not touching the stems).
In addition to ill timed pruning, probably the biggest reason for lack of bloom is winterkill or cold damage to the stems. The plant should be in a sheltered location and protected from winter winds.
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