For several years I walked by some blue mophead hydrangeas in my neighborhood that bloomed only sporadically. Every fall, the mow-and-blow gardeners would prune them down to 3 feet high. Ironically, they would've bloomed more if they'd been left unpruned. Finally, 3 years ago, I told the owner I could make them bloom more if I pruned them.
The first spring after I spent an hour or two pruning a whole row of mophead and lacecap hydrangeas, the shrubs were covered with huge, vivid flowers. Garden-party visitors who had their own recalcitrant bloomers asked about the secret to making them bloom.
It's no secret.
Any book on pruning will tell you that mophead and lacecap hydrangeas, which are cultivars of Hydrangea macrophylla, bloom on second-year wood. For a plant that's blooming in 2009, “second-year wood” is wood that was produced in 2008. (Newer cultivars such as All Summer Beauty bloom on the current season's growth.) It's a shame to keep watering these lush shrubs all summer, only to have them pruned into green boxes. And it's so simple to make them bloom prolifically, year after year.
I've been pruning these hydrangeas for three years, and each summer they're loaded with flowers.
Here's what to do: in the fall, look at the stems that have flowered. You can cut each of these stems back. Leave every other branch alone. That's it.
When I cut back the stems that have flowered, I do two things.
First, if the flower head is still in good condition, I save it as a dried cut flower and determine how long to make the stem. Hydrangea flowers will dry on their own and stay attractive for a year or more. All you need to do is remove all the leaves, including the tiny ones closest to the flower head, and place in a vase with no water. I usually cut more than needed, to ensure that a full bouquet is preserved.
Using hydrangeas as fresh cut flowers is more complicated. If you simply cut the stems and put them in water, the flowers will dry out and not last very long. You need to follow a series of treatments to keep the flowers fresh.
Second, if the branch is encroaching on a path or another shrub, I cut it back hard. Depending on how old the shrub is and how many stems it has, I may cut other branches hard to shape the shrub. Each cut should be just above a set of buds, above a set of leaf scars, or at a branch junction. Be careful not to nick any new buds!
As with roses, pruning lower on the plant will produce larger and fewer flowers, and pruning higher on the plant will produce smaller and more numerous flowers. Cutting into woodier stems is a gamble, however: you can either awaken dormant buds, or cut down so far that no viable buds have survived.
The hallmark of bad pruning, which is rampant, is a plethora of stubs. If you think of a plant's stems as a circuit, running from roots to leaves, it's obvious that any path not leading from root to leaf (or bud) is “dead.” The leaves act as engines producing food from sunlight and sending it to the roots. In turn, the roots suck up water from the soil and send it to the leaves. The stubs, outside the circuit, are open wounds that the plant cannot close, so they become susceptible to insects and diseases.
© 2009 Tanya Kucak