A Gardening Journal

Today in the Garden of a Lifetime: 'Quicksilver' Elaeagnus

Eleagnus x Quicksilver foliage flowers close up 053115 640

 

For years, I lusted after 'Quicksilver' for its foliage, whose bright silveriness is unique in shrubs hardy in Zone 6 and colder. No other silver-foliaged plant that you can grow in Boston (let alone Nome, Alaska) has foliage even remotely competitive. Yes, the bracts of Eryngium giganteum are as striking—but the rest of that plant (lovely as it is) is green. With the ephemeral exception of its pale-yellow flowers, 'Quicksilver' really is silver, and top to toe.

 

Eleagnus X Quicksilver overall 053115 640

 

What they lack in size and coloring, the straw-colored flowers make up for in number and fragrance. Their honey fragrance commandeers the garden. 

 

Eleagnus x Quicksilver overall B 053115 640

 

I hear that they mature to edible fruits that combine the flowers' pale yellow with the leaves' metallic shine; another common name for this shrub is silverberry. And their taste? Stay tuned.

 

 

Here's how to grow this unique silver-foliaged shrub:

 

Latin Name

Elaeagnus 'Quicksilver'

Common Name

Quicksilver elaeagnus

Family

Elaeagnaceae, the wild olive family.

What kind of plant is it?

Hardy deciduous shrub.

Hardiness

Zones (3)4 - 7.

Habit

Suckering and wide-spreading. The coarse branch structure is completely clothed Spring into Fall with narrow pointed leaves so densely dotted with reflective scales that they appear to be solid aluminum-silver.

Rate of Growth

Medium to fast.

Size in ten years

Height and spread depend on location and handling. Most vigorous and persistent—and large—where Summers are cool. There, six to twelve feet tall with indefinite spread. Can be kept much lower by pruning; see both "How to Handle it" boxes, below.

Texture

Out of leaf, the angular thorny branches are similar to those of pyracantha: awkward looking, and liable to project dangerously out into pathways. In leaf, the shrub is fluffy and dense, providing a saturated and bright silver presence unachievable by any other woody plant hardier than Zone 7.

Grown for

its foliage: Ah, to live in milder climates, where such silver-leaved stunners as Astelia 'Silver Shadow', Bismarckia nobilis, Dasylirion quadran- gulatumEucalyptus cinerea, Euryops pectinatusLeucadendron argenteumOlea europaea, and Senecio 'Sunshine' are possible. Gardeners who visit Hawaii can increase their "silver envy" by visiting the volcano on Maui to view the shocking white-grey rosettes of Argyroxiphium sandwicense subsp. macrocephalum. And gardeners everywhere can use Dichondra argentea 'Silver Falls' as a cascading skirt in Summer containers. But there is no other silver-leaved woody plant that combines the striking aluminum-white foliage of 'Quicksilver' with hardiness so deep that the plant could thrive coast to coast in Canada. Indeed, 'Quicksilver' foliage is so bright that gardeners in mild-Winter, cool-Summer climates (coastal Pacific Northwest, say, or the British Isles) still favor the shrub despite being able to grow some of the semi-tender options above. 

 

its flowers: Small but profuse yellow stars in clusters borne at the leaf axils, they are only modestly interesting visually. But their honey fragrance is pronounced as well as penetrating. I became aware of it by happenstance: I was racing by that portion of the garden and, all of a sudden, was aware of the strong smell of honey. Finally, I stopped and sniffed my way to the 'Quicksilver' source. The flowers are reported as maturing to marble-sized (but egg-shaped) yellow fruits, which are said to be bland but edible. (Perhaps the birds harvest them quickly; I don't ever recall noticing them but will keep a lookout this Fall.) They, too, have the shrub's characteristic metallic-looking scales and, so, provide another of the hybrid's common names, silverberry.

 

its hardiness and tolerance: poor drainage (especially in Winter) and high heat or humidity seem to be this shrub's only weaknesses. East Coast gardeners south of Pennsylvania should trial 'Quicksilver' only under ideal conditions; see "Culture" below. Elsewhere, the shrub is likely to be indomitable in almost any soil that isn't too damp, in any site that is more-or-less in full sun.

 

its unpalatability to browsers.

Flowering season

Mid-Spring, after the leaves have emerged.

Color combinations

The pale flowers reveal their yellow hues only at close range; otherwise they appear to be parchment or tan. The startling silver foliage goes with everything. I've never noticed a particular Fall foliage color, and sources don't seem to comment on one either. Perhaps everyone is still savoring the memories of the astonishing foliage color in Spring and Summer, and is gearing up to not look at the gaunt leafless contrast of the shrub's bareboned branches all Winter.

 

See "Plant partners," below, for options.

Plant partner

'Quicksilver' is unusual in that its Winter appearance isn't salvageable or disguisable by nearby plants. The shrub is a coarse branchy beast without its foliage, so cheer yourself up with the knowledge of how sensational the shrub will look when its foliage returns in Spring. Plus, by not bothering to enhance its cold-season aspect, you have all the more opportunity to jazz things up Spring to Fall.

 

If your scale is large enough, establish a free-range 'Quicksilver' colony and keep its height to five feet and lower (see the second "How to handle it" box, below). Accent its mounding and, literally, shimmering presence by letting the colony flow around an upright juniper that matures anywhere from ten feet on up. What about a specimen Juniperus chinensis 'Torulosa', or a grove of Juniperus communis 'Gold Cone'? The new foliage of the latter is a soft gold that might harmonize well with both the yellow(ish) flowers and fruit of 'Quicksilver'. Further, Juniperus communis goes toe-to-toe in tolerance of alkaline soil and drought—and hardiness: down to Zone 2. Alberta, Canada, isn't normally thought of for ornamental gardens other than alpine, but a sweep of 'Quicksilver' spiked with 'Gold Cone' would be worth the pictures, if not the plane fare.

 

If, like me, you grow 'Quicksilver' in less extreme conditions, where soil nutrition and moisture are average to good, the shrub would be a marvelous scaffold for clematis. Those forms with large flowers in saturated shades of blue, red, or purple would be particularly vibrant. Consider 'Romantika', 'Edo Murasaki', 'H.F. Young', or 'Rouge Cardinal'. For similarly intense contrast but on a far larger scale, plant Cotinus coggygria 'Velvet Cloak' amid a sweep of 'Quicksilver' handled as you would for pairing with one of the junipers above. The smokebush is also an easier partner than the clematis, in that it tolerates the same meager soil and water as does 'Quicksilver'. After my standards of Euphorbia cotinifolia are formed, I might set one of them near 'Quicksilver' for the same warm-weather jolt of wine-red and silver-white.

 

Because the entire shrub of 'Quicksilver' is an exceptional and exceptionally bright color—aluminum-white—the easiest pairing is always with any plant that's green. Almost any shade will do. In the pictures above, my 'Quicksilver' has a PG hydrangea to the left and a rose-of-sharon to the right. Each will bring big shows of pink flowers as Summer burgeons, but right from Spring, their "normal" green foliage is a welcome foil for the startling leaves of 'Quicksilver'.

Where to use it in your garden

The growth habit of 'Quicksilver' (vigorously stoloniferous) is as important as its shocking seasonal cycling from warm weather (fluffy-foliaged silver mounds) to cold (gaunt and graceless bare branches). One option is to site the shrub where it can grow as a pure colony. Then, most of its root sprouts will serve only to provide still more bulk and thickness, although the colony's outward expansion may still need to be controlled.

 

Keeping in mind the forlorn Winter aspect of natural-habit 'Quicksilver', choose a spot that is not unavoidable during the cold months. Plants with four-season appeal—or those that have a quick peak and then retreat underground in favor of the neighbors—are the ticket for such "ultra-prime" spots. (Poncirus trifoliata is at the top of my four-season list.)

 

Reserve the impact of this shrub's brilliantly bright foliage for a secondary focus in the garden, not one that you'll see every day from the kitchen window, or as you enter and leave your house from the street. In other words, site 'Quicksilver' around a corner or at the end of a secondary pathway, so its big show is a discovery—a surprise—not a quotidien inevitability.

 

If you grow 'Quicksilver' as a hedge, don't forget that you'll need to allow yourself room to handle the pruning—and that you'll also need to keep outward-bound root sprouts clipped down, too.

 

Given all of these caveats, fantasy locations would include a strip of dry and desparately sunny ground between two wide expanses of pavement: the perfect spot for a 'Quicksilver' hedge whose sprouting runners would (probably) be contained by the paving. Or a sunny corner bounded at the back by a building and at the front by similarly wide runs of paving. Siting 'Quicksilver' in the midst of a mixed border (as I do), where its root sprouts can be as widespread as its aesthetic pairings along the way are diversely beautiful, means a permanent commitment to control. That's the essence of any mixed border worth the name, true, so what's one more plant to wrestle with?

Culture

Full sun and almost any soil—acid or alkaline, nutrient rich or poor, heavy or light—that isn't overly wet in Winter. Dry soil is welcomed year-round. 'Quicksilver' is particularly vigorous in soils that are sandy and loose, not just dry; such soil could be essential for establishment of 'Quicksilver' in Zone 7 in eastern North America, which is the southern limit of this shrub's tolerance of heat and humidity.  

How to handle it: The Basics

This extremely hardy shrub can be planted at almost any time year-round that the soil is workable. Ensure enough water for establishment the first season but, unless you're gardening in actual desert conditions, further watering isn't usually needed.

 

If you are establishing your colony from divisions from a friend, these are best severed and transplanted in early Spring. Then the young shrub can root in securely over the Summer. Although Winter viability of Fall transplants isn't usually a problem, the challenge is that 'Quicksilver' is so hardy and so wind tolerant that it lends itself to sites so exposed that Winter storms could dislodge recent transplants, which are usually more-or-less bareroot.

 

In my experience, 'Quicksilver' responds only slowly to radical pruning, so keep shrubs at a convenient shape and size by lightly pruning the younger shoots. In other words, more attentive tip pruning is how you prevent young growth from becoming out-of-place major limbs. Go over the shrub in early Spring, then, to remove shoots that are already out of bounds, or likely to become so during the current season. Even so, some major pruning could be needed; see the second "How to handle it," below.

How to handle it: Another option—or two!

Growing 'Quicksilver' as a hedge is easy—but, even so, any hedge requires maintenance by definition. Given how stoloniferous 'Quicksilver' is, you could space plants widely and still expect to achieve dense enough growth for a hedge in a few years. For quicker coverage, planting every four feet is still close enough. You'll probably want to prune twice a season: lightly in early Spring, to remove shoots that are clearly out of line, or will soon grow to become so; and again in Summer, to shorten first-year twigs as much as possible so the hedge doesn't grow too large too quickly.

 

Because you won't be able to remove all the first year growth each year, the hedge will slowly increase in size despite your pruning. Eventually, you'll need to do more radical cutting-back to "reset" the hedge to its desired dimensions. 'Quicksilver' may respond more readily to severe pruning for you than for me, in which case you could just hack all limbs back substantially in early Spring. If response is slower, handle the reduction of a 'Quicksilver' hedge as you would one of beech: Handle just one of the hedge's three faces (two sides and the top) per year, pruning in Spring just as new growth is beginning. You'll usually need to prune one side the first year, so that you can then have close enough access to handle the top the second Spring, and the other side the third.

 

Use the same incrementalism to renovate (or keep in bounds over the long term) a free-range colony: Each Spring, saw one or two of the very tallest and thickest limbs down as close to the ground as possible. Then, younger stems emerging from ground level can receive more light and, so, mature all the faster. This is the same way that mature colonies of lilac are handled, so you can get in the groove and handle both at the same time.

 

There can never be too many possibilities for standards in general, let alone ultra-hardy ones with silver leaves.  Experiment with transforming 'Quicksilver' into a shimmering silver globe-on-a-stick by selecting a single main stem, providing a stake so that it assumes a tidy verticality. Clip off lower branches as well as root sprouts so that enough trunk is revealed as this main stem lengthens. When the exposed stem is the height you want—I'd suggest five feet but, then, again, I'm tall—pinch the tips of the stems above to encourage a well-branched head. Handle annual maintenance pruning as you would for a hedge, above.

 

Because 'Quicksilver' is so hardy, there's no need to time mid-season pruning so that resultant growth will survive the coming Winter. That said, you'll probably want to allow enough time for new shoots to appear, so that the bare Winter limbs—always awkward even in the best of circumstances—have at least the fuzz of young twigs on them, bare though they'll be. Pruning in early August is probably a good compromise: There's enough time for those new shoots to form, and yet the interval since the early-Spring pruning isn't so lengthy that the shrub has been able to grow completely out of bounds.

 

Gardeners in cool-Summer, mild-Winter maritime climates are reported as being able to grow 'Quicksilver' almost as a perennial, by cutting all shoots down to the ground in early Spring. Resultant stems could become two to four feet tall that same season, and would be a beautiful partner to nearby grasses and perennials. Let me know if this strategy is successful for you, too; my 'Quicksilver' plantings to date are in gardens with rich heavy soil, where 'Quicksilver' resprouts from radical pruning only slowly. 

Quirks and special cases

In my experience, 'Quicksilver' is a champion colonizer, and can send up sprouts from roots that extend several yards from the mother ship. This tendency is even more pronounced when the shrub is growing in loose well-drained dry soil where, presumably, there is much less risk of root rot.

 

When not in leaf, a free-range 'Quicksilver' gives no hint of its appeal Spring into Fall. Also, in my experience, the shrub doesn't tolerate the intense annual pruning that removes all the awkward old branches at once, as well as fostering graceful wand-like new ones, which makes pollarding and coppicing so easy and successful with, say, Catalpa, Paulownia, Cotinus, Acer negundo, Platanus, most Salix, and Tilia. And even if it did, there doesn't seem to be even a modest show of Winter bark that would thereby be enhanced. Lastly, while the foliage display is heightened when 'Quicksilver' is sited at the front of contrastingly dark foliage (see "Plant partners," above), it's throwing pearls before swine to backdrop 'Quicksilver' with a perfect yew hedge in hopes that the shrub will finally look like something in Winter. When a free-range 'Quicksilver' is the best choice for the warm months, don't waste time trying to mitigate the shrub's clunky look when it's cold.

 

Instead, site 'Quicksilver' such that it is appropriately focal and showy when in leaf, but out of the way when not. See "Where to use it," above. Or grow it as a hedge, which gives the shrub an overall geometry that is effective whether or not foliage is present. 'Quicksilver' is reported as tolerating the more frequent and less-intense pruning needed for training as a hedge; see the second "How to handle it" box, above.

Variants

Both of the presumed parent species of 'Quicksilver' present problems for gardens in eastern North America from Boston south. Elaeagnus angustifolia has already proven itself to be a notorious self-seeder, and should only be eradicated, not planted afresh. In my experience, Elaeagnus commutata is disease prone and eventually failing even in the comparatively mild Summer heat of southern New England, but should be a valuable shrub in climates that are somewhat to very much colder (down to Zone 3) as well as those that might also be drier in Winter. Gardeners from Vermont into Canada, as well as those in the Rockies, should try it.

 

E. commutata is also highly tolerant of salt (either present in the soil or from seaside spray), drought, and alkaline soil; its roots also fix nitrogen, so the shrub usually thrives regardless of poor fertility. Gardeners in maritime climates with relatively cool Summers (coastal Pacific Northwest, e.g., and all of the British Isles) may also find that Elaeagnus commutata will be at home; it isn't clear whether it requires cold Winters (in which case it wouldn't tolerate these mild-Winter locales), or just detests hot Summers.  

 

Berries of Elaeagnus commutata 'Coral Silver' are coral-red; the combination with the silver leaves should be thrilling. To my knowledge, there are no other forms involving either species that are gardenworthy.

Availability

Online; only rarely at retailers.

Propagation

By cuttings and by digging up divisions from suckering colonies at almost any time from Spring until early Fall.

Native habitat

Elaeagnus x 'Quicksilver' is thought to be a hybrid of Elaeagnus angustifolia, native from Europe across Asia to the Himalayas, and Elaeagnus commutata, native across Canada and south only as far as Minnesota, South Dakota, and Utah. Both species thrive in cold climates: E. angustifolia is hardy to Zone 2, and E. commutata to Zone 3. E. angustifolia is more tolerant of heat, and is successful to the point of being a challenging invasive to Zone 7. In my experience, even southern New England is too warm for E. commutata. It seems that 'Quicksilver' has combined the greater heat tolerance of E. angustifolia with the superior foliage of E. commutata, while also reducing (or even eliminating?) the propensity for self-seeding.

 

'Quicksilver' is a spontaneous hybrid that was discovered in England.

 
 
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