Crape Myrtle Trees

Everyone loves flowering trees.  When in bloom, they can change the entire look and feel of the landscape, especially if there are many trees planted throughout a property.  Ornamental cherries and pears make up the vast majority of the flowering trees that we sell at the nursery, but there are lots of lesser-used trees that are also very beautiful.  In recent years, we have had more and more customers including Crape Myrtles in their gardens.

The genus Lagerstroemia has more than 50 species, but most of the landscape-worthy plants we offer are within the species indica and fauriei or hybrids of those.  These deciduous trees and shrubs are native to India and Asia, including China, Japan and Korea.  They prefer full sun and fertile, moist, but well-drained soils.  Crape Myrtles come in a wide range of sizes and flower colors.  The leaves are a deep, lustrous green, and often turn amazing shades of red and orange in the fall.  Most cultivars have handsome bark, that exfoliates, giving the trunks an interesting mottled appearance.  The enormous paniculate (botanical jargon for many flowers joined together on a branched central stalk) flower clusters are borne on the tips of the branches and generally open in September on Nantucket.

Because these trees are technically marginally hardy here, we always suggest planting them in a protected spot in town.  In reference to Crape Myrtles, the authority on woody landscape plants, Dr. Michael Dirr states, “…-5 to -10 F is about the breaking point between a woody plant and herbaceous perennial.”  However, there are quite a few large Crape Myrtles on the island that have survived some of the colder winters we had a few years ago.

Crape Myrtles flower on new wood, so they are often pruned severely while dormant, forcing a lot of new growth annually.   That being said, I much prefer the look of a tree that is artfully pruned to a balanced framework instead of heading the entire plant back to an arbitrary height.  When pruned this way, they can have a lovely shape that is nice to look at, even when the branches are bare in winter.

We’ve had many cultivars over the years, but a few of the most common are listed below with their attributes:

  • ‘Biloxi’:  Pale pink flowers on a 20′ tall tree.
  • ‘Centennial Spirit’:  Wine red flowers on a 10-20′ tall tree.
  • ‘Hopi’:  Light pink flowers on a semi-dwarf tree – 7-10′ tall.
  • ‘Muskogee’: Lavender flowers on a large shrub or small tree – 15-20′ tall.  Britt’s favorite!
  • ‘Natchez’: White flowers on a vigorous, small tree – 20′ or more tall.
  • ‘Sarah’s Favorite’: White flowers on a vigorous, small tree – 20′ or more tall.  Anecdotally, a better plant than ‘Natchez’.
  • ‘Sioux’: Dark pink flowers on a large shrub or small tree – 14′ or more tall.
  • ‘Tonto’: Fuschia-red flowers on a semi-dwarf tree – 6-8′ tall.
  • ‘Tuscarora’: Coral-pink flowers on a large shrub or small tree.  15′ or more tall.

 

 


Sea Buckthorn

Working at the nursery as long as I have, there aren’t a lot of landscape plants suitable for Nantucket that I’m not familiar with, so I’m always pleased when I have the opportunity to learn something new.  Last fall, a customer asked about sea buckthorn, a plant I have absolutely no experience with.  After a little research, I think it might be a useful plant for some of the islands’ challenging sea-side properties.  We brought some in for a job this spring, and decided to order some extra for stock.  This plant should be a good choice for growing in close proximity to the shore, where soils are extremely sandy, drainage is excellent and sun is plentiful.

Hippophae rhamnoides has abundant grey/green, skinny leaves on thorny, branches.  Their habit is variable, sometimes reaching the size of a small tree, but they often treated as rangy shrubs.  The plants I have seen growing on Nantucket look quite a lot like Russian olives, although spinier and with narrower leaves.  These plants are dioecious, meaning that there are separate male and female plants.  If female plants are pollinated by males, they will have an abundant fruit set of small, yellow/orangy berries.  Native to the Northern regions of Europe, Asia and North America, sea buckthorn it is extremely cold hardy and can be expected to survive during prolonged periods of extreme cold.

There are many varieties in cultivation.  We’re currently stocking ‘Chuysaka’, ‘Hergo’ and ‘Juliet’.


Asian Wisteria

I’ve spent many, many hours on ladders and on top of roofs and pergolas as a professional gardener on Nantucket.  The bulk of those hours have been spent on rose care, but pruning and training wisteria is actually one of my all-time favorite garden tasks.  This graceful, spring-flowering vine requires a lot of work to keep in bounds and looking its best.  This is especially true of the Asian varieties, which are quite a bit more rampant than their North American cousins.  Although there are many cultivars and hybrids, Asian wisteria can generally be separated into to groups: Japanese and Chinese.

 

 

Japanese Wisteria, Wisteria floribunda

Flowers open over the course of days, starting at the top of the cluster.  Tendrils twine counter clockwise.

‘Black Dragon’ aka ‘Violacea Plena’ aka ‘Yae Koburyu’:  Deep purple double flowers

‘Domino’ aka ‘Issai’:  Lilac blue flowers

‘Lawrence’:  Pale lavender flowers

‘Longissima Alba’ aka ‘Siro Noda’:  Long white flowers

‘Snow Showers’:  White flowers

‘Honbeni’:  Pink flowers

Chinese Wisteria, Wisteria sinensis

Flowers tend to open all at once.  Tendrils twine clockwise.

‘Blue Moon’:  Bicolor blue flowers

‘Caroline’:  Very fragrant, bluish purple flowers

‘Cooke’s Purple:  Fragrant, bluish purple flowers

‘Jacko’:  Selection of Alba; very fragrant, white flowers

‘Prolifica’:  Bluish violet flowers

‘Royal Purple’:  Deep violet flowers

If you’re interested in how to prune these vines, check out our articles and Youtube videos on the subject:

Video – Summer pruning of Wisteria

Video – Winter pruning of Wisteria

Article – Summer Pruning How-to

Article – Winter Pruning How-to


Old Fashioned Lilacs

Having been a gardener and nurseryman on Nantucket for over 20 years, I’ve amassed a long list of favorite plants.  From year to year, the list changes as some plants become over-used and improved selections and exciting introductions hit the market.  Nonetheless, there are a few plants that will have a special place in my heart no matter what.  Old-fashioned lilacs are one of those.

When I was a child, my grandparents, Jim and Isabelle, had some common lilacs in their yard in Antigonish, Nova Scotia.  Fully mature, their stems had widened into trunks and they were so tall that we called them “lilac trees”.  Grandma would send us outside with kitchen scissors to cut the flowers and bring them indoors.  There were always extra to share, and we often brought some home to my Mom for our house too.  I also clearly remember Mom sending me down to our neighbor Theresa’s house to ask for a cutting of her lilac shrub.  We planted it at the edge of the lawn.  That lilac is now taller than I am and a lovely way to remember Theresa, who so kindly gave it to us, thirty years ago.

There are currently twelve species in the genus Syringa but only a few are cultivated in North America as garden plants.  Syringa vulgaris, common lilac, is the plant that comes to mind when most of us think of traditional lilacs.  There are many cultivars available, with flowers that range in color from crisp white, to deep purple-red.  There also numerous hybrids on the market that make great garden plants.  These lanky, suckering, shrubs grow 15-20 feet tall and can easily spread to occupy a space of 5 or more feet wide.  In order to keep lilacs looking their best, they do require a good pruning regimen.  Since the flowers appear on old wood at the tips of the branches, they can stretch out of reach as the plants get older.

Pruning is best done just after the flowers have faded in mid summer.  Keep in mind these objectives, while pruning:

  • Remove diseased or damaged wood
  • Encourage strong growth at the base of the plant, in order to combat the leggy habit
  • Keep the height of the plant in check, so that flowers can be enjoyed
  • Remove spent flowers, if desired

Consider following these steps while pruning:

  1. Take a good look at the overall structure of the plant.  Consider removing one or two of the oldest stems completely, at ground level
  2. Consider removing a few wayward branches
  3. Make several cuts at different levels to encourage new, bushy growth throughout the plant.
  4. Remove dead heads, making pruning cuts just above healthy buds.
  5. Assess the overall height of the plant, and make deeper, staggered cuts to reduce the height.

Check out our pinterest board for photos of old-fashioned lilacs we’ve carried in the past:

https://www.pinterest.com/surfhydrangea/luscious-lilacs/

Here’s a quick reference guide to varieties we’ve had in the past:

Syringa vulgaris aka common lilac:  Light purple flowers.  10-12′

Syringa vulgaris ‘Adelaide Dunbar’:  Deep purple buds open to double paler purple flowers.  French lilac.

Syringa vulgaris ‘Agincourt Beauty’:  Very large, deep purple flowers. 10-12′.

Syringa vulgaris ‘Charles Joly’:  Deep purple, double flowers.  8-10′.

Syringa vulgaris ‘Edward J Gardner’:  Light pink, double flowers.  8-10′.

Syringa x hyacinthiflora ‘Equinox Valley’:  Reddish-purple buds open to double light purple flowers.  8-15′.

Syringa x hyacinthiflora ‘Maidens Blush’:  Light pink flowers.  Canadian lilac.  Early flowering.  10-12′.

Syringa vulgaris ‘Madame Lemoine’:  White, double flowers.  French lilac. 15′.

Syringa vulgaris ‘Monge’: Reddish-purple flowers.  French Lilac. 8-12′.

Syringa x hyacinthiflora ‘Mount Baker’:  White flowers.  Canadian lilac.  Early flowering.  12-15′.

Syringa vulgaris ‘Nadezhda’: Double, lilac-blue flowers.  Mid-season. 8-12′.

Syringa vulgaris ‘Krasavitsa Moscovy’ aka Beauty of Moscow:  Very pale pink buds open to double white flowers.  12′.

Syringa vulgaris ‘Lavender Lady’: Light purple flowers.  12′.

Syringa vulgaris ‘Paul Thirion’:  Reddish-purple buds open to double pale purple flowers.  French lilac.  10-12′.

Syringa x hyacinthiflora ‘Pocahontas’:  Deep purple buds open to paler purple.  Canadian Lilac.  Early.  10′

Syringa vulgaris ‘President Grevy’: Violet-blue, double flowers.  French liac.  10-12′.

Syringa vulgaris ‘President Lincoln’:  Purple-blue flowers.  Mid-season.  8-10′.

Syringa vulgaris ‘Sensation’:  Reddish Purple florets, tinged in white.  French lilac.  Mid-season. 10-12′.


Summersweet

Walking around the nursery yesterday, I couldn’t help but notice the overall lack of color.  With so many deciduous trees on site, you would think we would have a riot of red, purple, orange and yellow leaves all over the place.  Unfortunately, Nantucket’s moderate climate doesn’t usually make for excellent displays of autumn leaves.  Most years, we go from a lush green nursery in September to rows and rows of bare twigs by mid November without much fall color in between.  I couldn’t help but notice a stunning show of yellow from a group of sweetpepperbush (aka summersweet) in the shrub area today, however.  On a dingy autumn afternoon, they really brighten things up.

Clethra alnifolia, as botanists refer to itis a native North American plant that is endemic to Nantucket where it can be found growing in low-lying areas and at the edges of wetlands.  If grown in moist soil, it tends to sucker and form colonies over time.  However, this plant is well-behaved and very adaptable, doing well in most any island garden where average soil and even water is available.  It prefers full sun, but will flower in shade.   The overall look of these plants is a pleasant green, twiggy shrub with an upright, balloon-shaped habit.  They have medium green, rounded, ovate leaves with finely-toothed edges.  In mid summer, they produce loads of fragrant flowers that are reminiscent of small, skinny bottle brushes.  The native form of this plant generally has white flowers, but there are pink cultivars available, as well.  Beneficial insects like it just as much as we do; many species of butterflies, bees, wasps, flies and other flying insects frequent the plant while it is in flower during July and August.

Clethra can serve many uses in the landscape.  If planted in a row, they make a great informal hedge that doesn’t require much pruning to maintain a tight shape.  I’ve seen them used very well in mixed shrub borders with both native and ornamental plants.  They make natural companions to bayberry, arrowwood, groundsel and beach plum, but look just as well among ornamental plants like butterfly bushes, vitex, shrub roses and spiraea. They respond very well to pruning and can be maintained at a height of five feet or so with an annual pruning.  Some gardeners prefer to remove the spent flowers while others leave them on the plant to be covered up by the new growth in spring.

There are many cultivars available in the trade as well as the straight species:

Clethra alnifolia The species form of this shrub.  Generally grows 3-4′ wide and 6 or more feet tall.  White flowers.

‘Anne’s Bouquet’:  White flowers.  Average size.

‘Hummingbird’:  Compact, white-flowered form.  2-4′ wide and up to 5′ high.

‘Pink Spires’:  Pink-flowered form, average size.

‘Ruby Spice’:  Pink flowers, average size.

‘Rosea’:  Pink flowers.  Average size.

‘Sixteen Candles’:  Compact, white-flowered selection with white flowers.

‘Vanilla Spice’:  Proven Winners introduction.  White flowers, touted to be larger than most.  Average size.


Viburnum dilatatum

Viburnum ‘Michael Dodge’

During the season, Surfing Hydrangea is a very busy place!  In order to keep the nursery full, we are constantly bringing in the staple trees and shrubs that landscapers are using day in and day out.  But luckily,  Craig is a plant geek at heart, just like me, so he also stocks a wide variety of lesser-known plants.  Over the last few years, we’ve been delighted to see a dramatic uptick in sales of our native arrowwood viburnum (Viburnum dentatum).  Arrowwood is a great shrub that can be used in a variety of applications, like medium-sized hedges and naturalized screening on property lines.  If you like the look of arrowwood, but want to try something a little different with showier fruit, check out linden viburnum (Viburnum dilatatum).  

 

 

This East Asian native has white lace-cap flowers and showy fruit in the fall.  The rounded/oval, toothed leaves are generally lustrous deep green with a quilted look.  Like many viburnums, Viburnum dilatatum grows well in evenly moist soils with average organic matter.  Plants thrive in full sun or part shade.  We have offered several cultivars over the years, some with red fruit, and some yellow.  Although this plant is self-fruitful, much of the literature mentions fruit set is improved with multiple varieties planted in close proximity.

  • ‘Asian Beauty’ has vigorous upright habit (10′) with deep green, thick, shiny leaves during the growing season.  This variety has cherry red fruit.  Fall foliage is maroon.
  • Cardinal Candy tm aka ‘Henneke’ is a Proven Winners introduction.  This selection is listed as 5-6′ tall.  The large, bright red fruit contrast very well with the dark green leaves, and persist long after the leaves fall in autumn.  Cardinal Candy is purported to have a heavy fruit set without additional varieties planted for cross pollination.  Foliage is reddish orange in fall.
  • ‘Michael Dodge’ is a stand out among viburnum, with bright yellow fruit.  This plant is said to grow 5-6′ tall.  Best fruit set is observed when planted with other varieties for cross pollination.  Fall color is reddish/orange.  Choose this variety over ‘Xanthocarpum’, an inferior yellow-fruiting variety, according to Dr. Michael Dirr.
  • Tandoori Orange is the first orange-fruited variety of linden viburnum.  This Proven Winners selection is similar to Cardinal Candy tm, and a good pollinator for other linden viburnum selections.

We have some stocky field grown ‘Michael Dodge’ and ‘Asian Beauty’ on the ground as well as some nice container grown Cardinal Candy tm.  We’d be happy to show them to you.

Viburnum ‘Asian Beauty’
Viburnum Cardinal Candy tm

 

 

 

 

 

 

 


Regular Pruning of Inkberry

Inkberry, Ilex glabra, is a beautiful, rounded, evergreen shrub that grow 5 – 8′ tall.  It prefers full sun and evenly moist acidic soil, but does well in wet areas and light shade.  When properly pruned, inkberry can make a nice foundation plant or short hedge, but is best used in native screens and rain gardens, where it can be left to grow naturally with little intervention needed from the gardener.  Young plants are perfectly round, with leaves right to the ground.  As plants mature, however, the canopy tends to shade out the bottom portion of the plant and their lower branches can become bare and leggy.  Regular pruning is required to keep inkberry looking its’ best.

Most applications for inkberry call for a plant that is maintained at 3-4 feet.  Once they reach this size, they need to be pruned at least once a year to keep in bounds.  Shearing with hedge trimmers (when new growth has just hardened off in early summer) is the easiest way to prune rounded shrubs.  Although this approach takes the least amount of time, repeated cycles of shearing can make the surface of the plant very dense, shading out the lower branches.  I recommend doing a more thorough pruning procedure every other year to open up the plant.  More light penetration stimulates new growth at the base and keeps the plant healthier overall.  Should plants become overgrown and overly leggy, a renovation can be done during the dormant period in winter or early spring.  I’ve actually cut overgrown inkberry to the ground while dormant and had excellent results.

There are several objectives when doing regular pruning on inkberry:

  • To remove dead or damaged branches
  • To maintain the proper height and shape
  • To keep the plant green from the ground up, (not leggy)

Understanding the growth pattern of these plants helps the gardener when making pruning decisions.  Growth in the upper portion of inkberry plants occurs in whorls.  A whorl is a ring of new stems that grow around a central, upright stem. There are many dormant buds between whorls on bare portions of the stems, even on the oldest woody stems.

On off years, when plants are not sheared, follow these guidelines:

  1. Remove any dead or dying branches completely, where they meet healthy growth.
  2. Pinch out most of the previous seasons’ growth just above a whorl to thin out the surface and keep the plant at the best height.
  3. Most cuts are made in the previous season’s growth, but several cuts can also be made into older wood, to stimulate growth lower down.
  4. As plants age, some of the oldest branches can be removed entirely at ground level in favor of younger, more vigorous growth.

There are several varieties of Inkberry available in the trade.  The most common are ‘Compacta’ ‘Densa’ and ‘Shamrock’.  Of the three, ‘Shamrock’ is the most highly praised by Dr. Michael Dirr in his extensive text book Manual of Woody Landscape Plants.  


Dormant-Season Renovation of Privet Hedges

Privet hedges are used all over the island as a beautiful way to border properties and break up large landscapes into smaller spaces.  In a lot of ways, privet is an ideal plant for tall hedges because it grows quickly and can be maintained at a relatively narrow width.  However, even well-maintained hedges slowly widen over the years, and established plantings will need a harder pruning every so often to stay healthy and in bounds.

Shearing hedges is a necessary part of maintenance, but this practice can cause problems in the long run.  When woody plants are repeatedly sheared, a dense layer of tiny twigs builds up on the outside, shading the interior stems and inhibiting dormant buds from sprouting.  As hedges age, dead wood can also accumulate in the center.  It’s not so much that it’s wrong to shear hedges; it’s more a matter of realizing that in order to keep a hedge healthy in the long run, renovation is required from time to time.  Removing the dense growth on the outside allows sunlight to fall on the dormant buds below, stimulating strong, healthy, new growth.  It also makes it much easier to saw out dead branches and scout for insect pests like scale and thrips that live directly on the bark.  This procedure is best done during the dormant season.

There are several ways to approach renovating a privet hedge.  Because privet grows rapidly, a declining hedge could be cut to within a few inches of the ground and allowed to completely regenerate.  If well irrigated and fertilized, one might expect 4-5 feet of growth in a single growing season.  This drastic approach won’t be acceptable in most situations.  I usually suggest that a hedge be renovated over 2 or three seasons, making deep cuts on one side per year.  Leaving one side un-pruned guarantees continued screening during the summer.  Although it can be nerve-wracking to make big cuts, be assured there are hundreds of dormant buds waiting just below the surface of each trunk and branch that will sprout once the sun shines upon them.

Be sure to use the proper tools for the job.  Branches narrower than ½” in diameter can be cut with regular hand pruners.  Branches up to 1” should be cut with sharp loppers.  Anything  wider than an inch should be cut with a hand-held pruning saw or chainsaw.

Consider following these steps:

  1. Choose the side that will be worked on. Rake all the debris out from under that side.
  2. Determine how much wood will be removed and set a string line along the ground as a guide for pruning. Make sure it is tight, and hovers above the ground without snagging on the lower branches of the hedge. 
  3. A second line can be strung at chest-height as well, but it’s a challenge to get it in place before pruning. Tie the string line onto sturdy stakes that won’t pull in allowing the line to sag as you are working.   Prune around the line, so that hangs freely and doesn’t snag on the branches.
  4. Start pruning on one end. Work from the ground up to as high as you can reach, establishing a vertical plane with the string lines as reference.  NOTE:  A properly pruned hedge has a narrow “A” shape; tighter at the top than it is at the bottom.  It is acceptable to maintain a 90 degree angle to the grade, but never allow the top portion of the hedge to splay out wider than the bottom.
  5. From time to time stand back and scrutinize your work. When you are right next to the hedge, it’s hard to judge whether or not it’s straight.  It’s much easier to stand at the end that’s completd and look down the length of the privet with one eye closed.  Move back and forth slowly and you can see any spots that still poke out past the string line.
  6. On taller hedges, you may need to make a second pass above your first to finish the job. Pole saws and pruners can be used.  There is even a chainsaw available that is on a long pole.  Personally, I much prefer using a sturdy ladder, or scaffolding made between two Little Giant ladders.  NEVER EXTEND A CONVENTIONAL CHAINSAW ABOVE MID-TORSO TO MAKE A CUT OR STRAIN TO TRIM A BRANCH JUST OUT OF REACH.  Always move your ladder to a comfortable working distance.  Don’t forget; the top should be narrower than the bottom.
  7. I suggest pruning the top each time you do a renovation, even if you don’t want to reduce the overall height. This extra step allows maximum sun penetration over the upcoming season.
  8. Once the major pruning operation is complete, make sure all dead wood is removed and take a good look at the bare wood remaining. Scale insects and thrips have become more of a problem on Privet over the last few years.  If large populations of any pest are found, consider applying a control.
  9. Power-washing has become widely used as a means of destroying tiny insects that overwinter on woody plants. Although I haven’t tried this approach, I have heard good things about its’ efficacy.  Power-washing is best done while the plants are still dormant.  If you are considering it, do your research and complete the process before buds begin to break in spring.


How to Prune Chaste Tree, Vitex agnus-castus

 

 

 

 

 

 

 

Now that the weather is cool and we’ve had a good hard frost, most shrubs have shed their leaves.  If you like to do your pruning in the fall, it’s time to get started. I’ve been cleaning up our garden over the last little while, and decided to prune our Vitex the other day.  It seemed like a good opportunity to review the best pruning practices for these great plants.

Before making any cuts, make sure you have your objective in mind.  For Vitex, pruning is generally done to accomplish a few goals – keep the plant healthy and shapely, with a great show of flowers the upcoming year.

 

 

 

 

 

 

 

First remove any dead, broken or whiskery twigs.  Weak growth will not be able to support a flower or fill out the main framework, so it’s best to direct the plants energy into stronger branches.  If there are any old branches in an area where new growth has begun to fill out the shrub, remove them right at ground level, in favor of the younger growth.

Next, consider the size and shape you want the plant to be in the next growing season.  Generally, the shrub will be rounded when pruning is completed with a balanced framework of branches that grow up and outward from the base.  Pruning cuts should be made just above a pair of buds.  Dormant buds can be hard to recognize at first; they look like little scaly bumps on the smooth branches.  Those buds will wake up next season and the new growth will have a huge flower on the tip in August.  If you were happy with the size and shape of the plant this past season, use previous cuts as a guide, trimming back side shoots to a single set of buds where they emerge from a main branch.  Most branches will have little “Y’s” at the top after this style of pruning.

Over years of pruning this way, the tips of the branches where the pruning cuts are made will form pollards (where many stubs have accumulated from regrowth at that node year after year)  When strong new growth no longer sprouts from the pollard, make a cut below, at the next set of buds, removing the pollard and allowing the plant to produce strong new stems.  If you find that your plant is getting a little leggy and bare at the bottom, make a few cuts closer to the ground, to encourage new shoots to fill out the bottom.

 

 

 

 

 

 

 

Vitex can also be grown as small multi-stem trees.  In that case, remove all but a few trunks rising from the base, and prune the upper branches less, to form a canopy.


Spicebush

We’re always on the lookout for plants that can solve problems for our customers.  We think spicebush, Lindera spp, might be one of those plants!  This wonderful native plant grows naturally from Maine to Ontario and Kansas and south to Florida and Texas.

This medium to large shrub, flowers in April on bare stems.  The yellow flowers remind me just a little bit of witchhazel, or winterhazel, but are smaller and held close to the twigs.  They are a good nectar source for insects waking up from their winter nap.  The mid-green, ovate, fragrant leaves turn yellow in the fall.  This plant is the sole food source for the spicebush swallowtail butterfly, and worthy of planting just to feed their caterpillars!  Similar to hollies, spicebush are dioecious, meaning they have separate male and female plants.  The males have somewhat showier flowers, but the females will produce red, elongated berries in the fall that feed migrating birds.

Spicebush is easy enough to grow in a wide range of soils and conditions.  Although they will have a denser habit in more sun, they perform well in part shade and do well in areas with moist soils.  Try planting it with arrowwood viburnum and Clethra in dappled sun.  Tall native perennials like Joe Pye weed and rose mallow would also make good companions.