Louis Raymond experiments in his own gardens like

a mad scientist, searching out plants that most people have

never seen before & figuring out how to make them perform.- The Boston Globe

…Louis Raymond ensures that trees can grow in Brooklyn…

or just about any other place where concrete consumes

the dirt and skyscrapers shield the sunshine.- USA Today

 
 

NEW Trips to Take!

Myrtle's easy when the conditions are right.

 
 
 
 

NEW Plants to Try!

Louis tries to capture the exact words to describe the fleeting but deep pleasures to be found in these Summer-into-Autumn incredibles.

 
 
 
 

New Gardening to Do!

Allergic to bees? You can still have an exciting garden, full of flowers and color and wildlife.

 
 
 
 

Plant Profiles

The Best Season Ever: Climbing Aster

aster-carolinianus-euphorbia-characias-silver-swan-112112-640

 

I wouldn't cross the street for such small, pale-lavender daisies—unless they're growing on a vine.  Hello, climbing aster.  The aster's foliage is modest green; the green-and-white leaves are those of Euphorbia 'Silver Swan', which happened to be sitting in the way of this vine's fast-growing stems.

 

Against other green foliage, the aster growth can seem to disappear.  Until flowers emerge in late Fall.

 

aster-carolinianus-112112-640

 

 

Here's how to grow this unusual vine:

 

Latin name

Aster carolinianus / Ampelaster carolinianus / Symphiotrichum carolinianus

Common name

Climbing aster

Family

Asteraceae, the Aster family.

What kind of plant is it

Perennial bulb.

Hardiness

Zones 7 to 9, sometimes listed as being hardy in Zone 6.  Easier to establish in the cold end of Zone 7 and into Zone 6 with careful siting.  See both "How to handle it" entries below.

Habit

Self-branching, producing many scandent stems that, in thriving plants, can become woody.  

Rate of growth

Fast when happy.

Size in ten years

Ten to twenty-plus feet tall and wide.  Mature size is dependent on a benign climate, astute siting, and choices you make in handling.  Shorter in less advantageous circumstances or when pruned back each Spring.  See "Culture" and "How to handle it," below. 

Texture

Medium; like most Fall-flowering daisies, climbing aster isn't grown for its foliage.  With its modest foliage, it is not showy when not in flower, but is perceived, rather, as neutral swagging amid the growth of a suitable host plant.

Grown for

its unique habit:  To my knowledge, Aster carolinianus is the only climbing daisy hardy colder than Zone 8b, roughly South Carolina.  Houseplant enthusiasts and gardeners in Zones 9 and warmer can also grow Mexican flame vine, Senecio confusus, with leaves somewhat like those of German ivy, Delairea odorata (which, despite its common name, is native to South Africa), but produces flamboyant flaming-orange semi-double daisy flowers similar to those of another Mexican native, Tithonia rotundifolia.  I'd be tempted to grow flame vine also, but it blooms mainly over the Winter, when the only person who would see it in the greenhouse is me.  So for climbing daisies that flower during the warm months, Aster carolinianus is it.    

 

its flowers: Compared to those of a typical non-climbing "terrestrial" aster, the flowers of Aster carolinianus are nothing special: one-inch semi-double blooms with pink-to-blue ray flowers and yellow disk flowers.  Given that there are no other choices even remotely hardy in New England for vines with daisy flowers, though, the flowers of Aster carolinianus are fantastic.

Flowering season

Late Summer: October or November into December.  Flowering isn't deterred by mild frosts.   

Color combinations

To my eye, the pink-rose-faintly-blue flowers of Aster carolinianus make the plant suitable only for gardens that restrict themselves to pink, rose, burgundy, blue, and white.  Thank goodness I have one.

Partner plants

Aster carolinianus will most often be grown with some sort of support.  Yes, you could grow it as a large-scale groundcover, letting its stems ramble along, but why not just grow non-vining forms of aster instead?  Yes, if your garden offers both the necessary mildness of climate and also a high enough retaining wall or rock ledge that faces south or west, you could plant Aster carolinianus at the top, and let it form a large and spectacular cascade.  But that's a mighty unusual set of circumstances.  Typically, Aster carolinianus needs to be planted where it can climb through or be tied to support that will result in its growth being held much higher and wider than the plant's base. 

 

Fence, trellis, and wires screwed into walls are some of the options for support that is constructed.  Here are possibilities for support that's living: 

 

If you're trying to establish Astor carolinianus in Zone 6 or colder, you might first grow an espalier of something evergreen against a south- or west-facing wall.  The bulk and complexity of the evergreen foliage and branches will make it easy for the aster stems to explore upward and outward through them; the host shrub's evergreen growth also baffles Winter wind even as it also creates sun- and heat-trapping pockets.  I have long-established espaliers of Magnolia grandiflora, Cedrus deodara, and Cryptomeria japonica, all of which are espaliered against south- or west-facing walls for the very same reasons of the wall's ability to block cold wind from the east and the north, and to maximize exposure to hot south and west sun.  These espaliers currently host such also-a-bit-tender vines and scandent shrubs as Gelsemium sempervirens and Stauntonia hexaphylla.  Perhaps there's room for Aster carolinianus.

 

If you have your heart set on Aster carolinianus romping up through a host plant that is an aesthetic inspiration but not an overwintering godsend, do what I'm going to do with one of my climbing asters:  Grow it in a large nursery pot (ten-gallon, say) that, in early Spring, you sink within the aster's reach of the intended host.  My host will be the blue-needled, burgundy-coned Pinus koraiensis 'Silveray', amid which the aster's grey-green foliage and lavender-pink flowers would be very exciting.  The vine will root out into the surrounding soil over the Summer; if you sink the pot completely into the soil, and mound some up over the crown of the aster itself, the clump will also root into that top layer of soil.  Dig up the potted vine in late Fall or early Winter before the weather is too severe, and store the plant in a cool greenhouse or, if it's become leafless and truly dormant, in a cool and humid frost-free environment, such as a sparsely-heated basement.  Because you're overwintering the potted aster in shelter, it's OK to cut back its stems to a foot or so to make the digging-up and schlepping easier.

 

Gardeners in Zone 7 and south can site Aster carolinianus anywhere it receives plenty of sun and also has access to a host plant with the somewhat open and rangy habit that will provide easy purchase for the aster stems.  Evergreen hosts are still a good choice, in that their foliage helps mask the bareness of the aster stems in Winter.  Hollies and boxwood will usually be too dense; even if the aster stems can penetrate, there isn't enough light to encourage the deeper exploration that will anchor the stems well.  Instead, consider evergreens with looser foliage and a "gappier" habit.  What about siting the aster on the sunny side of Magnolia grandiflora, Cephalotaxus sinensis, or Daphniphyllum macropodum?  Or you may be lucky enough to have a haystack-sized colony of old rhododendrons, whose sunny side would be much more interesting in October and November if it sparkled with hundreds of lavender daisies.

 

Keep in mind that your woody host for Aster carolinianus will need to be large enough to not be overwhelmed by the aster's enthusiasm; in Zone 8 and warmer, the vine is reported to grow to twenty feet.  Any woody plant that big is also going to have an impressively extensive root system.  Site the aster several feet out from the farthest extent of the host's foliage so the aster's roots are less likely to be in direct competition with those of its host.

Where to use it in your garden

Where solidly hardy—from solid Zone 7 south: central Virginia down to north Florida—Aster carolinianus can be planted anywhere it gets plenty of sun.  The woody stems enable it to drape around mail-boxes and to swag split-rail fences.  The stems aren't attractive in the Winter, though, so consider a full-sun site that isn't in full view as you enter and leave your house.  

 

Partnering with a living host instead of a fence or pergola gives you much more flexibility, especially if the host is evergreen, because its bulk and greenery will help make the aster's leafless stems less of an eyesore.  See "Partner plants," above.

 

Colder than Zone 7, Aster carolinianus can survive only if sited where it can enjoy various microclimatic advantages.  See "How to handle it: Another option—or two!," below.  Those considerations will trump the purely aesthetic options available to gardeners in warmer climates.  There won't be any mailboxes at the roadside of Berkshires farms that can be swaddled with climbing aster, but there might be a west-facing stone or brick wall against which the aster can be reliably grown.

Culture

Full sun except in Zones 8 and 9, where the plant is solidly hardy and can persist even with a bit of shade.  Nutrient-rich soil and plenty of moisture ensure the most vigorous growth in the warm months, and therefore the largest crop of flowers, although in its native range, the plant can be found growing almost anywhere, in almost any kind of soil.  Good drainage in the Winter enhances hardiness in Zone 7, and is a prerequisite for experimental siting in Zone 6.

How to handle it: The Basics

As is typical for plants that flower in the Fall, Aster carolinianus should be planted only in Spring.   Locate on a slope, no matter how slight, so that surface water is passing through instead of settling in. 

 

Even though young plants, especially in Spring, don't give a hint of their plans to scramble through anything handy from June on, be proactive in providing support.  Almost any fencing or trellis will do, as well as adjacent plants that are large enough, sturdy enough, and open enough to securely host the aster's wide-ranging stems and, by mid-Fall, profuse crop of flowers.  See "Plant partners," above.  

 

Absolutely restrain yourself from doing any tidying beyond deadheading when flowering is complete in late Fall.  The stems are likely to look dead at best, but must not be disturbed until Spring.  Even then, wait until the plant is awakening before approaching it, pruners in hand.  

 

If the plant has enough space to grow ad libitum, you need only cut off any dead tips or broken portions.  Older stems become woody, and can be allowed to resprout.  If the clump has grown large enough to become a space-hog, Spring is the time for drastic pruning.  Handle the plant as you would a buddleja, cutting stems back only to their lowest point of active growth.  If this spurs them to form new growth even lower, you can then cut back to it.  If stems are also emerging from the base, you can feel free to cut woody stems right to the ground.

 

Aster carolinianus is scandent, not vining, so stems will need to be woven through trellis or chainlink, or tied to fence rails.  If growing through a living scaffold (see "Partner plants," above), it's usually sufficient just to poke the lose end of the occasional stem back into host's tapestry of branches to keep everything in place.  Because the vine does best in full sun, find a balance between growing it far enough into the branches for secure anchoring, but not so far that its progress is slowed by increasing shade.  From August on, let the vine sprawl and drape at will in the maximum sun at the surface of the host, so that it can produce the largest crop of flowers.          

How to handle it: Another option—or two!

Without other options for climbing daisies of comparable or even approximate hardiness, it's worth the work to establish Aster carolinianus in a climate that's somewhat colder than its normal range.  Try to make use of as many tactics as you can to enhance the chances of successful overwintering.  Aster carolinianus is usually thought to be reliable only in Zone 7 and warmer, so if you're gardening in Zone 6 and colder, you need all incremental advantages.  

 

If possible, site with a south- or west-facing wall to the back, and train the stems up wires or trellis that's just an inch or so out from the wall so that the main stems of the vine are held snugly against the wall.  The aster's late-season growth will billow out from the wall (and beautifully so when the plant is in flower), and if you gently tie that growth back to the trellis or wires when flowering is through and hard Winter is imminent, you can then fasten a sheet of wind-baffle fabric across the front of the wall.  (As is typical for Fall-flowering plants, it's best not to trim any stems of Aster carolinianus until the following Spring.)

 

Also choose a location that provides a slope, even a small one, for surface water to drain away from the wall, i.e., to drain farther south or west.

 

In late Fall, mulch the base of the clump heavily, without snapping the stems growing up from it.  It may then be possible to rest a rectangle of plywood or, even easier, the large lid from a heavy plastic storage bin, diagonally in front of the clump.  If this improvised lean-to rests in part against the mound of mulch, it won't impinge on the upward stems of the aster.  This will protect the clump from wind, and also shed rain.  Hold the lean-to in place by setting a couple of logs of firewood against the outside of it.

 

Yet another help would be to train stems of climbing aster up through evergreen growth of a shrub or tree you've espaliered to that same wall.  See "Partner plants," above.

Any (other) quirks or special cases?

I keep forgetting to check, but the flowers of Aster carolinianus are reported to be fragrant.

Downsides

If only Aster carolinianus were a zone hardier, I could plant it in the garden outright.  Its preference for reasonable drainage in the Winter, however, makes it an unlikely success story in most of my garden beds, where heavy soil is often the reality.  I hope to square this circle by growing the plant in a large container, sunk into the ground only for the Summer.  See "How to handle it: Another option—or two!," above.

Variants

To my knowledge, there are no named variants of Aster carolinianus.  I would be delighted to know of a source for plants whose flowers are distinctly to the blue end of the species' spectrum.

 

Availability

On-line and, where solidly hardy, at specialty retailers.

Propagation

By cuttings and by seed.

Native habitat

Aster carolinianus is native, appropriately, to North and South Carolina, as well as Georgia and Florida.   

 
 
FacebookTwitterRSS Feed

Stay in touch!

 

Sign up for twice-monthly eNews, plus notification of new posts:

 

* indicates required