Even Improved Hydrangeas Want Attention
Posted by Tony Tomeo on Aug 7, 2012 - 7:43:03 AM
LOS ANGELES—After decades of breeding, most modern cultivars of hydrangea are much more compact and a bit stockier than old fashioned hydrangeas that had long, limber stems that could bend downward from the weight of their own blooms. They stand up to proudly display their modern, vibrant color, even when their billowy blooms get heavy with rain. Yet, even with all their genetic improvements, they should still be pruned properly and annually to promote continued bloom. Without pruning, even modern cultivars can get floppy and lanky.
Because most hydrangeas bloom on stems that developed during the previous year, they should not be pruned too much while dormant through winter. Instead, solitary (generally unbranched) stems that grew from the base last year and bloomed this year should be pruned back to a pair of buds about a foot high as their blooms deteriorate. Even though some blooms continue to develop late into autumn, most are finishing about now. Therefore, pruning stems back while also removing spent blooms gets the pruning done early enough for the side buds to start to grow into secondary stems.
These secondary stems should not get pruned again, even when they go dormant through winter. They do not grow much before winter, but should be mature enough to bloom during the following spring. Thinning these branched stems through winter by cutting some of the smaller stems to the ground should produce fewer but significantly larger blooms, as well as prolong the blooming season. (However, many modern cultivars naturally bloom sporadically after their primary bloom phase until autumn anyway.)
New canes that develop from the ground to replace older branched stems may not bloom their first year, but can be left unpruned through winter to bloom early the next spring, which starts the process over again. Old stems should be cut to the ground after their third year (second bloom season). Leaving a few spent blooms on the plants long enough to dry (as dried flowers) should not interfere too much with proper pruning.
Flower of the Week: Hydrangea
Things were simpler decades ago when hydrangeas, Hydrangea macrophylla, were either white or not white. Those that were not white were mostly pink locally because of the alkaline soil of most of Southern California. Blue hydrangeas where seen in isolated spots of coastal mountains farther north where soil is slightly acidic, or where the soil was amended to be acidic. (Acidity causes flowers to be blue. Alkalinity causes flowers to be pink.)
Now there are more than five hundred cultivars of hydrangea! Although bloom color is really determined by pH, many cultivars make better blue shades, and many others make better pink shades. Purple and red have been added to the mix, while white has become less common. After getting pruned low while dormant through winter, most hydrangeas grow about three or four feet tall and broad through summer. Some can get twice as large, while many stay low and compact.
Most hydrangeas have 'mophead' blooms, which are large, round 'panicles' (clusters) of smaller sterile flowers. 'Lacecap' blooms are flat topped panicles with narrow borders of the same small sterile flowers surrounding lacy centers of minute fertile flowers. Hydrangeas bloom from early spring late into autumn.