Heavenly hydrangeas

If a yard should be considered an "outdoor room," as most garden designers insist, then a hydrangea's place in the garden can be likened to that of your living room sofa.

You can't sit on a hydrangea, of course. But when one is in flower, it becomes the focal point - drawing all the attention and compliments to itself (and away from those areas that may not look as good).

With hydrangeas, as with sofas, you can even change color schemes as often as you like. In the mood for blue? Big-leaf or garden hydrangea (Hydrangea macropylla) will oblige if you make sure its soil is acid. Prefer pink? Just raise the soil's pH, so it's alkaline. Want more variety than that? Some cultivars have lavender flowers and others, almost red. Change the mood by going for lacecap flowers, which have a delicate look.

Or instead of letting a hydrangea become the center of attention, use it as a foil to show off nearby plants. If you choose kinds that have pristine white blooms, you can surround the shrub with flowers of any - or all - colors. No clashing here. Some excellent whites are:

• Smooth hydrangea (H. arborescens Annabelle), which has exceptionally large flowers on a 5-foot bush.

• Pee Gee hydrangea (H. paniculata Grandiflora) has pyramidal blooms up to 12 by 18 inches, on a plant that may grow 20 feet tall.

• Oakleaf hydrangea (H. quercifolia) is a native that's ideal for shade. But it generally isn't hardy where winter temperatures drop below minus 10 degrees F.

All these hydrangeas bloom for a long time, which is one reason they're so popular. But a new cultivar, Endless Summer, is ever-blooming from June until frost. After the first flush of blooms fades, new ones develop - over and over. It has also proven to be extremely cold-hardy.

The big question with hydrangeas often is: Why didn't it bloom? There are two common reasons: (1) A late spring frost killed the flower buds; and (2) pruning, which removed the flower buds. If necessary, Pee Gee hydrangea may be pruned yearly, in very early spring, but the only time to prune a garden hydrangea is immediately after it finishes flowering. (Annabelle and oakleaf hydrangea rarely need pruning.)

And should you decide you want to move your sofa ... uh, hydrangea ... to another spot, feel free to dig it up and do so. After all, you're the decorator.