Powell Gardens' Spectacular Summer Flowering Shrubs

There's nothing like a border of summer flowering shrubs to brighten up these sun saturated days. We often think of spring flowering shrubs but there are good choices for all seasons and here are some of the best shrubs for flowering NOW!

The border near the trolley stop of the Rock & Waterfall Garden is currently at peak bloom with hydrangeas and rose-of-Sharon; two of our most brilliant summer flowering shrubs.

The border contains our best display of Limelight Hydrangeas (Hydrangea paniculata 'Limelight'), which is just now transforming from lime green to white as the flowers mature. Limelight's flowers are mostly sterile, which gives it that full look but does not provide much for beneficial insects and wildlife like the fertile "lacecap" types. All paniculata hydrangeas are easy to grow in our climate and are very forgiving of bad weather and bad pruning. They bloom on new wood so can be cut back in spring for huge blossom stalks OR they can be allowed to grow into large shrubs; many can even be trained (pruned up) into delightful little trees.


The cultivar 'Quick Fire' is an early blooming and fertile lacecap cultivar (in full white bloom back on the solstice) and has already aged to a lovely rosy-pink, soon to deepen to deeper tones
--a quick fire indeed.

The cultivar 'Unique' is a spectacular white, fertile variety that attracts many beneficial insects to its pollen and nectar. What a spectacular choice for a white, evening or moon garden! This mass is in the Perennial Garden but it can also be seen in mass on the Island Garden.

The cultivar 'Pink Diamond' is also in full bloom now and will soon age to a good pink. It is also a fertile "lacecap" type that is a good insectaries garden plant (will attract many beneficial bugs to your garden to help control the bad bugs!). This picture is from the Island Garden (a nice contrast to purple-leaved Diabolo Ninebark to the left). We also have a mass of Pink Diamond Hydrangeas in the Perennial Garden.

Here is a closeup of 'Pink Diamonds' lovely flowers: note the big sterile white flowers set about the smaller fertile flowers inside that have the pollen and nectar for the good bugs.

Rose-of-Sharons (Hibiscus syriacus) is also a spectacular shrub now in bloom. Yes these are hardy, first cousins to the tropical hibiscus and the perennial rose mallows. The cultivar 'Blue Satin' is depicted from near the Rock & Waterfall trolley stop. Our favorite blue-flowering cultivars are 'Bluebird' and 'Coelestris' but they are difficult to find at nurseries anymore. Rose of Sharons become large shrubs 8 to 12 feet tall. Their drawback is that many cultivars self-sow wildly in gardens (luckily not in undisturbed soils so are not considered invasive).

The white-flowering 'Diana' Rose-of-Sharon is a hybrid from the National Arboretum that sets no (or very few) seeds. This is a premier evening garden plant because Diana also holds her flowers open at night while many Rose-of-Sharon close up in the evening. Other sterile National Arboretum Rose-of-Sharon are 'Aphrodite' with pink flowers and 'Helena' with lavender flowers; both good choices where you want the great bloom but NO seedlings to pull.

The Butterfly Bushes (Buddleia davidii) are spectacular this season as none of them died back with the mild zone 7 winter here. This is the cultivar 3-in1 which sports white, pink, mauve and dark indigo flowers. It should be called four-in-one and this shrub is in a "white phase" as these shrubs can sometimes flower mostly one color then another! This is a neat conversation piece shrub and the butterflies love it. It is NOT grafted and literally sports out various colors of flowers through the growing season.

The first picture of 3-in-1 Butterfly Bushes was taken on the west side of the Island Garden's pools: here's what the 3-in-1 Butterfly Bushes on the east side look like! These are a wider mix of colors though the one in the foreground is also in a white phase. Purple Coneflowers make a nice companion planting.

Autumn Sage (Salvia greggii) is a Southwestern native shrub long considered hardy only in zones 7 or warmer. Newer cultivars like 'Furman's Red' depicted have proven hardy here and are actually small shrubs that bloom all summer with peak bloom in the fall. They are a hummingbird favorite and appreciate a dry, well-drained site as shown in the Island Garden's living wall.

The Summersweet Clethras or Pepperbushes (Clethra alnifolia) are also in bloom now. This is a full shrub of the new Plant of Merit cultivar 'Ruby Spice' on the Island Garden. Its wonderful aroma perfumes the walkway along the Island Garden, much to the delight of visitors. Summersweet Clethras are superior shrubs for Evening Gardens for this reason.

Here is a closeup of 'Ruby Spice' clethra's flowers. If only we could transmit its scent through the Internet. Most Summersweet Clethras are white flowering but 'Ruby Spice' is the best pink flowering cultivar. Clethras can range from short 4 foot shrubs in the cultivar 'Sixteen Candles' to tall 8 foot plus if you buy the plain species. They are native to Coastal regions of the eastern United States and Canada and are very hardy into zone 4. They like extra moisture so are great rain garden shrubs.

The mild winter also allowed the Crape Myrtles (Lagerstroemia spp.) to gain more size again. Almost all Crape Myrtles now on the local market are new hybrids that have improved hardiness: Great flowers from the more tender L. indica and improved hardiness from the chestnut-barked but poorer flowering L. faureri. Most of the new hybrid crape myrtles have Native American names but not all. The cultivar depicted is 'Catawba' which is the best purple-flowering variety we can grow. Look for Catawba Crape Myrtle in the Perennial Garden.

The cultivar 'Zuni' has lavender pink blooms and is in full bloom just outside the Visitor Center. Crape Myrtles will not set bud until warm nights of 70F! They need hot weather to perform so are right at home here. (It's one thing that you can't grow well in London or Seattle!) They are marginally hardy and will die back if it is colder than -5F or so. They bloom on new wood so will return and bloom from the roots if they are killed by winter. Many crape myrtles are reaching unprecedented heights of 20 feet in Greater Kansas City as recent winters have not killed them back: long time gardeners have told me that this has never happened here before. I still warn new gardeners that they could so don't count on them as small trees even though many big box stores sell them as such. They are one tough, spectacular summer blooming plant; oblivious to heat and drought. They come in a wide array of colors from white ('Acoma' -- a Plant of Merit) to pink ('Hopi'), red ('Dynamite' may be the best red) and all shades in between. Newer cultivars may also have dark burgundy leaves that really make the flowers stand out.

All photographs taken Sunday, July 27, at Powell Gardens.