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North Hills Monthly

Hydrangeas 101

Jul 31, 2016 08:19PM ● By Denise Schreiber

One of the questions I get asked most often is about hydrangeas—why aren’t they blooming in the garden? So let’s try to simplify the mystery.

There are six main types of hydrangeas that are grown in the United States, although there are about 49 species total. Only four of them are native to North America. The ‘hydra’ part of the name comes from the seed capsules’ resemblance to ancient Greek water vessels.

First is the climbing hydrangea, (Hydrangea petiolaris) which requires a sturdy trellis or arbor. It is hardy to Zone 4 and blooms on old wood. No pruning is required. The big leaf hydrangea (Hydrangea macrophylla) is hardy in our area and some of its varieties include flowers called lacecaps. This is the hydrangea sold at florists for Easter and Mother’s Day. It blooms on old wood and shouldn’t be pruned, and should be protected in the winter from wind and the local fauna.

An old-fashioned hydrangea that many people have in their yard is the peegee hydrangea (Hydrangea paniculata). This is more of a tree form with cone-like flower blossoms. It is very hardy (Zone 3) and blooms on new wood, which means that you should prune it in late winter or very early spring. You may be familiar with some of the newer introductions such as Pinky Winky or Limelight.

Hydrangea arborescens is called the smooth hydrangea, with cultivars such as Annabelle, Incrediball and the Invincibelle series. These are hardy to Zone 3 and bloom on new wood, so pruning should occur in late winter or early spring. The advantage that I have found with Annabelle is that the deer like to nibble on it during the winter, thus doing my pruning for me. This type of hydrangea has a huge flower head and is ideal in vases.

The oakleaf hydrangea (Hydrangea quercifolia) had large leaves that look like oak leaves, hence the name. The leaves turn a beautiful scarlet color in the fall and the spent flowers take on a pinkish tinge. The mountain hydrangea (Hydrangea serrata) is hardy to Zone 5 and it too blooms on old wood and doesn’t require pruning. Mountain hydrangeas also have lacecaps in their family.

It takes a couple of years for hydrangeas to establish a well-developed root system. When planting, dig a hole that is 1-1/2 times the size of the root ball or container. You shouldn’t plant them in a windy area or an area where water will pool and freeze. Other than pruning at the wrong time, the only things that might prevent flowering are not enough light or problems with deer eating it.

All hydrangeas prefer at least four hours of sunlight (preferably morning light), moist soil and cool roots, which mean that they should be mulched. They are very shallow-rooted, so use just a couple of inches of mulch, and keep it away from the trunk of the shrub. You can use a balanced fertilizer such as 10-10-10 to feed the shrubs. Water the flowers deeply at least once a week or twice in very hot weather.

Everyone wants to know how to turn their hydrangeas pink or blue…and I can tell you definitively that placing pennies, foil, rusty nails or aluminum nails in the soil will not change the color of your hydrangea. The only hydrangeas that can reliably change colors are the big leaf and mountain varieties; other hydrangeas are going to stay the same color no matter what you try. Color change is dependent on two things—the pH of the soil and the presence of aluminum in the soil. In order to change the color, you have to apply aluminum at certain times in very specific amounts. 

If you want to preserve the flowers, mix a solution of 50 percent glycerine and 50 percent boiling water. Stir and let it cool. Make fresh cuts on the hydrangea stems, and then place them in a vase containing the mixture. Allow them to absorb all of the liquid until it is gone and then spray them with an acrylic sealer (found at craft stores). If you try to dry them without doing this process, the flowers will shatter, leaving you with just stems.