A Gardening Journal

Variegated Rockspray Cotoneaster

 Cotoneaster-horizontalis-Variegata-Euphorbia-tirucali-Sticks-on-Fire-090513-640

 

For the moment, ignore the succulent candy-colored stems. I'll profile that plant next. Right now, focus on the arching stems and small variegated leaves. Variegated rockspray cotoneaster is one of the most elegant of all hardy shrubs. And it's very easygoing: You can train it up or down, tall-and-wide or tall-and-narrow—or you can let it arch outward and downward at will.

 

The white-edged leaves are small enough—barely a half inch—that they don't obscure the intriguing array of the branches themselves. Long main stems grow two ranks of side branches, which are so orderly and held so cleanly in the same plane that the likeness to the spine and ribs of a flat fish, such as a flounder, is uncanny. Hence, one of the common names, fishspine cotoneaster.

 

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The subtle contrast of the bright variegated leaves with the dusty burgundy of the young stems couldn't be more satisfying—except that, in Fall, the foliage also colors rosy plum. The juxtaposition of the Cotoneaster with the riotously colorful stems and foliage of Euphorbia tirucalli 'Sticks on Fire' is, possibly, all the better for being temporary: The euphorb doesn't tolerate frost at all, so is a potted specimen that, just by chance, was set near the Cotoneaster.

 

In the photo below, a pairing for the long-term. I'm leading the top stems of the Cotoneaster into the dense blue-green growth of the adjacent semi-dwarf larch. Now the shrub's subtle details of color and geometry are on full display.

 

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Here's how to grow this easy and elegant shrub:

 

Latin Name

Cotoneaster horizontalis 'Variegatus'. Also listed as Cotoneaster atropurpureus 'Variegatus'

Common Name

Variegated rockspray cotoneaster

Family

Rosaceae, the Rose family.

What kind of plant is it?

Sprawling shrub. Nearly evergreen at the warm end of its range; deciduous in Zone 6 and 5.

Hardiness

Zones 5 - 7, but more susceptible to diseases in Zone 7 of the eastern North America, with its characteristic hot and high-humidity Summers. Easy in the colder Winters and comparatively cooler Summers of eastern North America's Zones 6 and 5. Succeeds in Zone 8 and 9 of a cool-Summer maritime climate, such as that of the Pacific Northwest, Ireland, and the United Kingdom. 

Habit

Unless trained, wide spreading and groundcovering or, if given the opportunity, cascading.  

Rate of Growth

Medium.

Size in ten years

Growing free-range on reasonably level ground: two to three feet tall, five to eight feet wide. Growing free-range with access to an opportunity to cascade, as from the top of a retaining wall: The same dimensions on the uphill side of the cascade, but (probably) not cascading farther than three or four feet. As an espalier, to eight or even ten feet tall and, potentially, to twice that in width. As a free-standing staked weeping tree, possibly to eight or ten feet tall. 

Texture

Graceful, thanks both to the branching pattern and the foliage. Long central stems are ranked on both sides with numerous side branches, reminiscent of the array of ribs on the spine of a fish. Small orderly leaves call attention to this geometry instead of obscuring it.   

Grown for

its foliage: Pairs of small pointed gray-green leaves are irregularly edged in white. In Fall, they turn rosy-plum. They are nicely spaced along dusty burgundy twigs; twigs and foliage each show the other off to advantage.

 

its habit: As in "Texture," above, gently arching stems with a fishspine branching pattern are distinctive year-round. As branches grow outward, they layer atop earlier generations, forming a tiered mound of growth that succeeds as a groundcover.

 

its small pink flowers, which are, along with those of Pyracantha, reported as occuring at a time when comparatively fewer other flowers are available to bees. The flowers are profuse and modestly showy. The red berries that follow are of a similarly low-key quality.

Flowering season

Late May / early June. 

Color combinations

As proved above, by its warm-weather association with the carnival-like coloring of a potted Euphorbia tirucalli 'Sticks on Fire', the white and gray-green foliage, plus soft burgundy bark of young stems, enables Cotoneaster horizontalis 'Variegatus' to harmonize with almost anything: Pink, yellow, orange, purple, and green. If 'Sticks on Fire' had any blue in it, that would fit right in, as well. The red berries that appear in Summer only add to the party. In the cold months, the Cotoneaster leaves are shed; the bare bark isn't distinctively colorful, and the berries have long since been eaten by birds. Cotoneaster horizontalis 'Variegatus', then, offers its unusually broad range of color-coordination possibilities in Spring through Fall.

Plant partners

Cotoneaster horizontalis 'Variegatus' is easy to integrate into mixed plantings as long as it isn't unduly shaded by its neighbors. When used as a foreground or groundcover, then, be sure that possible shade-casting partners are sited only to the North or East of the Cotoneaster; as long as it receives light from the West and South, its growth will be nearly as vigorous as if it had received full sun all day.

 

Because this Cotoneaster has such a detailed variegation and a delicate look, juxtapose it with plants with simple and large details, and just one direct link to the shrub's color palette. (In this regard, my nearby pot of Euphorbia tirucalli 'Sticks on Fire' is a firm example of "Do as I say, not as I do.") Consider the Cotoneaster as a groundcovering fronter for Cotinus coggygria 'Velvet Cloak', whose dark rounded leaves will echo the shrub's burgundy bark. Or back the Cotoneaster with almost any conifer, especially one, such as the Larix I used, whose needles celebrate the blue-green of the Cotoneaster leaves.

 

Given how multi-layered and groundcovering the arching branches of this Cotoneaster become, it's a challenge to have low groundcovers nearby. They'd become shaded out as they arch downward into the foot-high growth of, say, pachysandra. Or they'd eventually grow thickly enough to shade out the (say) pachysandra, itself. Further, the outward growth of the Cotoneaster is steady, if not truly speedy, so you'd need to be comfortable with losing another foot or so of groundcover each season. 

Where to use it in your garden

The arching and cascading habit of Cotoneaster horizontalis 'Variegatus' makes it a natural—and an enjoyable one, at that—for use on banks or at the top of ledge or retaining walls. Its stems' distinctive fishspine branching pattern and reasonable flexibility make the shrub even more exciting when trained against a wall. When given such support, growth can be even longer—to eight or even ten feet.

 

The sun-loving nature of this Cotoneaster suggests that it be placed at the front of a bed. But there, its outward-then-downward arching branches would be intent on nosing out into adjacent grass. This makes mowing a hassle, and if the shrub were clipped to solve that, the shrub is given an artificially-restrained look that is, on that one side, at least, at clumsy odds with the tiered arching freedom of the rest of the shrub. In short, plant this Cotoneaster where it fronts wide paving, out onto which it can flounce gracefully, or site in a deep planting pocket amid steep ledge, or at the front of a bed atop a retaining wall. Few shrubs relish the opportunity to cascade with such grace, and take advantage of the chance with such style. Or (nearly best of all), espalier the shrub, letting new branches arch outward from the espaliered ones. Then the Cotoneaster provides its own higher elevation from which to cascade.

Culture

Full sun is best, although some shade is tolerated. Good drainage is essential, even if it is achieved at the expense of moisture-retentiveness and overall content of organic matter. Established plants are quite drought-resistant. 

How to handle it: The Basics.

Plant in Spring or Fall. Cotoneaster is usually available only as container-grown plants, so there is none of the shock that could accompany handling of stock that is balled and burlapped. Growth is fast enough that a mass planting can be established with a density of only two plants per square yard. 

How to handle: Another option—or two!

To espalier Cotoneaster, the usual method of training against a wall is the best: Space horizontal wires a foot apart up to the desired height of coverage. In addition to their principal anchoring, with a heavy screw-eye at either end, insert an additional screw-eye every three or four feet along the length of each. Then, tie bamboo poles diagonally to the wires as needed, so that branches can be fanned upward as well as outward by tying them loosely to the poles. Go over the shrub yearly—mid to late Summer is probably best—when there's new growth at the tips of branches that can be tied in, and ties farther down the branch can be redone or even, if the branch has matured enough to be rigid, removed.

 

As a branch reaches the end of a given length of bamboo, the cane can be removed (or extended farther outward to receive still more new growth). The older portion of the branch can then be tied, loosely but securely, directly to any horizontal wires it crosses. Remember that, if your climate brings heavy snow and ice in Winter, the wires need to be anchored securely to the walls, and the poles and branches securely to the wires. As you train the shrub in Summer, then, be mindful that you're also training the shrub to remain attached to its supporting structure despite the rough weather that Winter will bring in only a few months.

 

Cotoneaster branches have a distinct top and bottom. As you espalier them, you'll be retraining those branches at ninety degrees, with their top sides facing outward, and their bottom sides facing back into the wall. As you train a young or adolescent Cotoneaster espalier, you'll want to help it make the most progress in filling out its desired space by training its branches so that they continue to face forward. They, they'll grow upward and side-to-side, not arching outward and downward. 

 

Depending on your style of gardening and the space available, you have two choices on how to handle an espaliered Cotoneaster that is nearing its desired size. You could clip off additional growth that is no longer needed to extend the coverage, which will also help maintain a simpler structure that will, handily, also highlight the fishspine branching pattern more clearly.

 

You might, however, choose to let some of the new Cotoneaster stems arch outward and then downward, i.e., to grow in their normal orientation, not rotated ninety degrees against the wall. Depending on how many such branches you allow to grow naturally, your espaliered Cotoneaster will acquire a lush and also bulky cascading habit: Such free-form "swan diving" branches might arch outward a foot or two even before beginning their descent. If you have the room for such an extraordinary display, go for it.

 

Keep in mind, however, that the branches of the shrub that are anchored to the espalier wires will need to be all the more firmly attached, as will the espalier wires themselves: The weight of snow or ice that could become stuck to the twiggy and unattached cascading stems would be substantial, indeed. It would be a tragedy to train such a Cotoneaster cascade for years only to have it be broken apart because it couldn't support snow- or ice-load. Instead of mere wires-and-screw-eyes, then, train a Cotoneaster espalier that is also intended to become a cascade to a rigid metal grid that is bolted to the wall. Yes, the cost would be substantial, and the installation a matter for the professionals. But given the years or even decades that the Cotoneaster cascade would take to create as well as enjoy, even such a substantial initial investment would be, amortized over the long term, really worth it.   

 

In my garden, I'm leading my Cotoneaster horizontalis 'Variegatus' up into an adjacent semi-dwarf larch, Larix laricina 'Deborah Waxman', whose dense shrubby habit makes its branches fairly accessible even for a naturally-prostrate shrub such as the Cotoneaster. All that was needed was to tie one of the Cotoneaster branches to a short stake so it could get a leg up into middle-range branches of the Larix. The natural arching habit of the further growth of the Cotoneaster branches helps integrate them into the twiggy growth of the larch; they just need to be pointed in the right direction. Their very twigginess and leafiness synergizes with the dense larch growth, enabling new Cotoneaster growth to mesh securely, on its own, farther and farther upward and into the broadly-mounding branches of the larch.    

 

Yet another option would be to train a single main branch up a permanent stake, letting its side branches extend and elaborate ad libitum. You'll soon have a small weeping tree, perhaps six feet tall, eight at the most.  

Quirks and special cases

The branches have a sense of touch: If the shrub is sited where its branches come into contact with ledge, individual boulders, or masonry with a bit of complexity (such as a flight of stairs), the growth habit changes from outward and arching to a flowing cascading veneer.

Downsides

Cotoneaster can succumb to a number of pests and diseases; cultivars vary in their resistance. C. horizontalis var. perpusillus, below, is particularly at risk of contracting fireblight.  Check with your local branch of the USDA Cooperative Extension Service to verify if fireblight is a problem where you garden. As is so often the case, respect for a plant's desired growing conditions—for Cotoneaster, great drainage above all—can reduce susceptibility.

Variants

Cotoneaster is a large genus; depending on whether subspecies and varieties are classified separately, there could be anywhere from about seventy to three hundred species. They hybridize easily, so new forms of Cotoneaster are inevitable. The red fruit of C. horizontalis 'Dart's Splendid' is particularly bright and profuse. The habit of C. horizontalis var. perpusillus is notably more prostrate. The foliage of both cultivars is plain green.

Availability

On-line as well as at nurseries and garden centers.

Propagation

By cuttings collected in Summer, or by layering branches that are naturally touching the ground.

Native habitat

Cotoneaster horizontalis is native to Western China. 

 
 
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