Lackluster climbing hydrangea, gangbuster runners

What else can we attribute to an overly warm winter?

My climbing hydrangea hasn't bloomed and doesn't look like it will. It usually does. What a loss. Could I have done this by pruning it at the wrong time last year? - A.H. -

 

If climbing hydrangea (Hydrangea anomala) is pruned late in summer, after the next year's buds are formed at its branch tips, that can reduce its next spring bloom by however many tip buds were clipped away.

Your pruning and this year's performance may be totally disconnected, however. Climbing hydrangeas all over our watch -- and we've been watching them from the Great Lakes to the East Coast -- are not blooming well this year. Flowers are absent, few or have so few showy petals that a viewer may overlook them entirely.

A case might be made that climbing hydrangea (H. anomala petiolaris) is such a gorgeous plant that we shouldn't press our luck and ask for bloom. However, we have seen it bloom fabulously in other years and sure missed it this year. We bet the butterflies were disappointed, too -- this one is often loaded with yellow swallowtails when its fragrant flowers open.

When something like this happens over such a large area we figure a big-ticket factor has to be involved. Something a lot of far-flung gardeners might have in common. For instance, the weather.

It makes sense. Temperature and hydrangea blooms are already linked. Growers who force potted mophead- and lacecap hydrangeas to bloom out of season have proof that other hydrangeas' flower bud development requires a certain level and duration of cold between the end of one season and the beginning of the next. They also know for certain that if temperatures are too warm during the bud's second stage of growth, after dormancy, the blooms may be small and lack color.

Climbing hydrangea isn't a pot crop  grown for forcing but it may share its cousins' developmental needs. In that case, the unusually warm winter and spring just past may have nipped your vine's bloom more completely than summer pruning ever could.

The climbing hydrangea inflorescence is huge -- that's one flower cluster circled in orange, below. However, the fertile flowers that make up the majority/center of the flower are fairly dull. What the human eye admires are the sterile flowers that ring the fertile cluster. Those aren't numerous, and have just one set of petals. There goes the show, if their white petals fail to develop because they did not receive the requisite hours in unbroken below 40°F.

Then there's human timing to consider, too. Did we just fail to look up in time to see climbing hydrangea blossoms in their prime (below, left)? Once they pass peak (below, right), they don't command much notice.