In the Garden:
Middle South
October, 2007
Regional Report

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The overwintered buds on this 'Endless Summer' hydrangea were killed by last spring's late freeze; fortunately, the plant also flowers on new wood.

Prolong Spring with Repeat-Blooming Shrubs

We can get strawberries in winter and apples in spring, so why not lilacs in fall? We consumers are used to getting what we want, when we want it, and transcontinental shipping has made out-of-season produce available year-round. Now, plant breeders are hard at work developing shrubs that flower in seasons beyond their usual bloom time. Often called repeat-bloomers, these shrubs put out the usual flush of flowers in spring, followed by sporadic blooming all season long.

The attraction isn't just the novelty. Gardeners -- especially those with limited space -- want plants that will bloom for more than a week or two in spring, and repeat-blooming varieties of azalea, hydrangea, lilac, and viburnum fit the bill.

Old Wood, New Wood
Some trees and shrubs produce flower buds on old wood, and some on new wood. The distinction is simple. Plants that bloom on old wood set buds for their blooms during the previous growing season. Rhododendrons, for example, set buds in late summer, buds that overwinter and then burst into bloom in spring. Butterfly bush (Buddleia), on the other hand, blooms on new wood -- on stems that are produced during the current growing season.

Why is this important? Because it determines how you care for the plant. Prune your rhododendron in late winter and you'll be cutting off flower buds. You might choose to do this to renovate an overgrown shrub, but know that you'll sacrifice some of the blooms. Spring-blooming shrubs like rhododendrons, azaleas, and forsythia should be pruned right after flowering, so they can grow and set buds during summer and fall.

Butterfly bush, on the other hand, can be cut back hard in late winter -- you can even cut it right back to the ground. Hard pruning in late winter encourages vigorous spring growth, and this new growth will produce buds and flowers in summer. Summer- and fall-flowering shrubs like butterfly bush, summersweet (Clethra alnifolia), and blue-mist spirea (Caryopteris clandonensis), are best pruned in late winter.

Repeat Bloomers
Azaleas. Most azalea varieties produce a flush of blooms in spring; some also produce a few fall blooms. Breeders have been trying to enhance this trait by crossing these natural repeat bloomers with the rarer summer-flowering species to develop shrubs that will bloom reliably in spring, summer, and fall. The Encore series of azaleas, for example, includes 23 varieties chosen for their repeat bloom. The Bloom 'N Again azalea series includes seven repeat bloomers.

Hydrangeas. Most mophead hydrangeas (H. macrophylla) -- the ones with huge round clusters of pink or blue flowers -- bloom in early summer on old wood. Now breeders have introduced varieties that form additional flowers on the current season's growth. Examples include 'Endless Summer', 'Blushing Bride', 'Forever and Ever', 'Pink Shira', 'Sadie Ray', 'Forever Pink', and 'Penny Mac'. Hydrangeas range in size from 18 inches to 12 feet at maturity, so check plant labels carefully. (Some "dwarf" varieties grow 8 feet tall!)

Lilacs. I associate lilacs with my birthday in late May, since that's when the common lilac (Syringa vulgaris) is usually in bloom. These shrubs prefer cool climates and require a long winter chill, making them a challenge to grow in Zone 7 and warmer. Some lilac hybrids, however, are not only more reliable in warmer climates, they also boast repeat blooms. Pink-flowered 'Josee' lilac (Syringa x Josee), for example, may rebloom three or four times during the growing season if you diligently remove faded flowers. 'Tinkerbelle' (Syringa 'Bailbelle') is also reputed to repeat bloom. Like hydrangeas, lilac varieties vary in size from 4 to 20+ feet so choose carefully.

Weigela. Many weigela varieties boast "scattered" repeat bloom, but some, such as Carnaval, Red Prince, Rumba, and White Knight, are touted as flowering reliably, if intermittently, throughout summer and into fall.

Viburnum. The only reliably repeat-blooming viburnum, 'Summer Snowflake' (V. plicatum var. tomentosum) doublefile viburnum produces its first and most dramatic show in spring, with occasional blooms popping out here and there through summer and into fall. Also unique among viburnums is its tall and narrow shape, with a height of up to 12 feet but a spread of only 6 feet.

I have mixed feelings about repeat-blooming shrubs. While I love a long season of blooms, I also like how the flowering of different plants -- and the availability of different foods -- marks the passage of the seasons. The sweet smell of lilacs -- and the taste of the first ripe strawberry -- coincide with my Gemini birthday, and like birthdays, their fleeting nature makes them even more special.


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