From my perspective as a hydrangea, the most critical thing you need to understand about me is my flowering schedule. This is not a one-size-fits-all answer, as it depends entirely on my species. My blooming habits are genetically programmed, and your deadheading actions must align with this internal clock to avoid accidentally removing next year's potential blooms. Essentially, you need to know if I bloom on "old wood" or "new wood."
If I am a Bigleaf hydrangea (Hydrangea macrophylla), an Oakleaf hydrangea (Hydrangea quercifolia), or a Mountain hydrangea (Hydrangea serrata), I bloom on "old wood." This means the flower buds that will burst open this summer were actually formed on my stems during the previous growing season. They have been patiently waiting, protected by tiny scales, all through the fall and winter. If you cut these stems back heavily in the fall or early spring, you are cutting off my entire floral display for the coming year.
Therefore, the best time to deadhead me is immediately after my flowers fade in the mid-to-late summer. At this point, my energy is shifting from sustaining the spent bloom to strengthening my roots and stems for winter. By snipping off the faded flower head just above the first set of large, healthy leaves, you are giving me a clear signal. You're telling me not to waste energy on producing seeds and instead to focus on storing resources. This encourages me to set robust buds for the next cycle. Waiting too long, like in the fall, is risky as any new growth I might produce after the cut won't have time to harden off before frost, making it vulnerable to winter damage.
If I am a Panicle hydrangea (Hydrangea paniculata) or a Smooth hydrangea (Hydrangea arborescens), like the popular 'Annabelle', I operate on a different schedule. I bloom on "new wood." This means I create my flower buds on the fresh, new growth that emerges in the current spring. This gives you, the gardener, much more flexibility. You can even cut me back to the ground in late winter or early spring, and I will still push up new stems that will flower that same summer.
For deadheading, you have two primary options. The first is to deadhead me after my blooms fade in the late summer or fall. This is purely for aesthetics, tidying up my appearance as my large flower heads turn brown. You can simply snip off the old bloom. The second option is to wait until late winter or very early spring and combine deadheading with your annual pruning. At this time, you can cut back the stems, removing the old flower heads in the process. This winter approach has an added benefit: the dried flower heads provide some visual interest in the winter garden and offer minimal protection to the top set of buds on the stem from harsh weather.
When you deadhead me correctly, you are sending a precise hormonal signal throughout my system. The faded flower was a "sink," drawing energy to potentially produce seeds. By removing it, you eliminate that sink. My energy, derived from photosynthesis in my leaves, is then redirected. It flows down into my crown and roots, strengthening me for the winter, or laterally to encourage the development of other buds. It’s a collaborative effort. You provide the gentle guidance with your shears, and I respond by allocating my internal resources more efficiently, which often results in a more vigorous plant and, ultimately, more blooms in the seasons to come.
