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Re-Blooming Hydrangeas

I have a follow-up question to your recent article about hydrangeas not blooming. While the explanations offered are helpful for old-fashioned varieties, I’d appreciate some advice for the hydrangeas that bloom on both old and new wood. These varieties should bloom regardless of harsh winter weather or late frosts & freezes. If the proper type of fertilizer is used and still no blooms come, what other variable can explain the absence of bloom? I really want my hydrangeas to be the beautiful, showy shrubs they are promoted and advertised to be, but I am pretty frustrated at this point. Thanks for your help.

The re-blooming hydrangea is a wonderful plant whose powers perhaps got a little distorted in all the excitement when it was introduced. There seems to be confusion between the terms re-blooming and ever blooming. Given the right conditions these shrubs will repeat bloom after the first flush, but they do not bloom continuously. There is also a misconception that re-blooming hydrangeas are ideal for any climate. To uncover the mystery behind why your hydrangeas are not performing as promised, it’s good to know how re-bloomers behave compared to the standard, old-fashioned varieties.

Old-fashioned, bigleaf hydrangeas (Hydrangea macrophylla) flower from buds formed on the tips of the stems the previous year. The buds are produced in response to the shorter days and lower temperatures as we approach fall. These hydrangeas bloom the next summer in one glorious show unless the buds are damaged by fall pruning or an especially cold winter or late spring freeze.

Some hydrangeas form buds up and down the stems the previous season, not just at the tips. Because the buds are lower down the stem, closer to the earth, and protected by the foliage of the shrub they can survive lower temperatures than the buds on the tips. They often also escape late season pruning that can eliminate the upper bloom buds. These hydrangeas are called perpetual or free flowering because these lower buds may mature weeks after the first flush of bloom. This makes the blooming period of the shrubs longer.

The beauty of a re-blooming hydrangea is that it will produce flower buds during both the previous season and the current season. If last year’s buds are destroyed by inadvertent pruning, winter temperatures below 10 degrees or a late spring freeze, you can still count on the plant to set new buds on the current season’s growth. This is good news for gardeners in regions where, because of winter hardiness, getting hydrangeas to bloom is difficult.

They are ideal for the Midwest where the winters are usually cold enough to kill the flower buds formed the previous season and yet the warm season is long enough for the shrub to grow, set new bud and bloom before the first fall freeze.

However, in areas where summers are exceptionally short even the re-blooming varieties are not always successful. Typically re-blooming hydrangeas need 12 weeks to produce blooms on new wood. If last fall’s buds are killed over the winter, the growing season may not be long enough for the plant to grow, mature, and bloom before the first autumn frost.