Answer: The key to successfully getting your Hydrangeas to flower is understanding how and where they produce their flower buds. Hydrangeas come in a multitude of species and varieties, and all we basically need to know is which group they fall into.
Group 1: Some species bloom on new growth (current new growth).
Panicle Hydrangea( H. paniculata), and, Annabelle Hydrangea (H. arborescens), all flower on this year?s new growth.
These species bloom reliably each year and require no special care to produce flowers. These plants can be pruned in the spring, fall or winter and they will still bloom the following year.
Group 2: Some species bloom on old growth (last years stems)
French Hydrangea or Bigleaf Hydrangea (Hydrangea macrophylla) and Serrate Hydrangea (Hydrangea serrata-These species typically have colorful flowers (blue, pink, red-pink, lavender, or white etc.,) that are either large balls (mopheads) or flat and lacy (lacecaps). Group 2 includes Oakleaf Hydrangea (H. quercifolia) and Climbing Hydrangea (H. anomala)
The real challenge is consistently producing flowers on varieties that bloom on last year?s stems. Although Group 2 plants (H. macrophylla and Hydrangea serrata.) are hardy enough to survive in zone 5 and into zone 4, their flower buds are prone to damage either by an early frost on autumn, a late frost in spring or excessively cold temperatures when dormant in winter. This, along with untimely pruning, can result in inconsistent flowering or no flowering at all.
For growing Hydrangea macrophylla and Hydrangea macrophylla var. serrata types in zones 4 and 5, the following solutions have been tested successfully in Michigan and Maine?s northern interior: Don't prune unless necessary. Pruning often removes the flower buds. If you need to prune, remove any dead stems in the spring. Any other necessary pruning should take place immediately after bloom. The new flower buds form in autumn, when night temperatures consistently drop below 60 degrees.
Cover the plants to a depth of at least 12-18 inches with mulch, bark, oak leaves, pine needles, or straw. Cover the entire plant, tips included, if possible. Remember not to use maple leaves because they will mat when wet and can suffocate the plant. Some people make cages out of snow fence or chicken wire to hold the mulch. One creative gentleman, who every year has a spectacular Hydrangea garden, uses 20 gallon plastic trash cans. He cuts off the bottoms, places them over his plants in early winter, fills them with mulch and then puts the lid on them until spring.
Remove the mulch only after any major threat of frost (50% frost-free date) has passed. For the Mid-West Michigan that is around May 15th. Do not be concerned if there are small white leaves and stems they will survive and turn green again quickly.
If this is too much work - then consider growing the first group of Hydrangeas listed above.
Hope this answers all your questions!
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