A Gardening Journal

The Best Season Ever: 'Ruby Lace' Honey Locust

Purple foliage is easy to have in coleus and elephant ears, smoke bushes and beeches, maples and crape myrtles, succulents and dahlias. In plants whose leaves are pinnate, however, it's oddly scarce. In fact, your choices are only two.* In mild to hot climates, plant 'Summer Chocolate' mimosa. But where temperatures sink to zero degrees Fahrenheit or lower, 'Ruby Lace' is it. 

  

When light passes through the new foliage, it glows rosy and even pink.

 

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When the light on the new foliage is direct, not transmitted, its color is burgundy. The shine of the young leaflets provides a beautifully contrasting sparkle.

 

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But then, the foliage matures, and the burgundy, rose, and pink of youth are cast aside for the greenish mud-brown of maturity. Ugh!

 

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'Ruby Lace' is rarely grown, and its drab adult foliage is certainly one of the reasons. Fortunately, you can ensure that your 'Ruby Lace' forms very little mature foliage—and keeps it hidden beneath loads of richly-colorful juvenile foliage that continues to emerge all season long.  Read on! 

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* OK, there is also a purple-leaved walnut but, to my knowledge, it is not commercially available in North America. Even in Britain, Juglans regia 'Purpurea' is extremely rare in the trade. One of the few known specimens is in the Belfast Botanic Garden.

 

Here's how to grow this unusual ornamental tree:

Latin Name

Gleditsia triacanthos f. inermis 'Ruby Lace'

Common Name

Ruby Lace honey locust

Family

Fabaceae, the locust family.

What kind of plant is it?

Deciduous hardy tree. 

Hardiness

Zones 4 to 9. Doesn't tolerate the combination of high heat and humidity and clay soil typical of the American southeast; but might be possible there when growing in sandy coastal soils. But why not grow Albizia julibrissin 'Summer Chocolate', instead? It adores sweltering heat and drought, and its foliage is more delicately divided, and significantly darker.

Habit

Upright and single-trunked, but the canopy tends toward irregularity and seeming confusion about the shape it is striving for. For my money, the best usage of 'Ruby Lace' is as a pollard, which simplifies its habit while also intensifying the color of its foliage. See, below, "How to handle it: Another option—or two!"

Rate of Growth

Medium.

Size in ten years

Possibly fifteen to twenty feet high; somewhat less wide.

Texture

Feathery and, indeed, lacy.

Grown for

its new foliage, which is a medium-dark burgundy. The color of mature foliage is, admittedly, odd: A deep tan with aspirations to olive green. 

its ability to provide purple pinnate foliage in climates too cold for Albizia julibrissin 'Summer Chocolate', which is hardy in Zone 6 only in ideal circumstances (perfect drainage in Winter, all possible sun and heat year-round), and is reliable only in Zone 7 and warmer. That tree thrives in high heat and drought, and will grow even in tropical deserts. By contrast, 'Ruby Lace' is hardy to Zone 4 and, as is typical of Gleditsia, prefers climates with long cold Winters, comparatively short Summers and, in general, pronounced changes in climate from season to season. 'Ruby Lace' is the only purple, pinnate-leaved plant that is reliably hardy in Zone 6 and colder, so we should be most grateful to have it. (Wouldn't a purple-leaved wisteria be a thrill? A purple-leaved trumpet vine? Even after countless millions of these and other hardy pinnate-leaved shrubs and trees have been grown the world over, dark-foliaged forms have still not been identified.) 'Ruby Lace' foliage is never darker than oxblood; even so, this is a dramatic contrast to the green of the straight species. But the foliage of 'Summer Chocolate' is even more striking, in that in direct light it approaches ebony. On the other hand, the transmitted light of 'Summer Chocolate' is a disappointing olive green, whereas that of the new foliage of 'Ruby Lace' is pink and rose.

 

 

See "How to handle it: Another option—or two!" for the way to minimize the amount of drab mature foliage your 'Ruby Lace' tree carries. Happily, this also maximizes the proportion of the new foliage, whose directly-reflected color (oxblood) as well as transmitted colors (pink and rose) are all pleasing, indeed.

Flowering season

Late Spring and, so, emerging after the foliage. My trees have yet to flower and, as pollards, are unlikely ever to begin doing so. The flowers emerge from growth that was initiated the previous year, which is just the growth that is removed by the pollarding. But no matter: The flowers—greenish yellow, in short pendulous racemes— are not especially showy anyway.

Color combinations

In direct light, the young foliage appears as a rich burgundy, and can mix with just about any other color: Burgundy is famous for its ability to get along just as well with pink as with orange, blue as with red, white as with yellow. But when the foliage is lighted from behind (as would happen if you look west toward your 'Ruby Lace' in late afternoon), then you'll also see light that is passing through its leaves. This transmitted glow reveals the tree's inner pink-and-rosiness. 

It would be difficult to site 'Ruby Lace' in the full sun it requires while also ensuring that it is viewed only via light that is direct, not transmitted. Better, then, to embrace the pink brought out by transmitted light, and surround 'Ruby Lace' with plants that are either neutral (white, silver, or green) or pink-friendly. See "Plant partners," below.

Plant Partners

When grown as a pollard, 'Ruby Lace' can combine with perennials and shrubs in a mixed border, where its small head of lacy foliage can float above the majority of plants that will be filling the space from ground-level up to about six feet. Its lacy and comparatively dark foliage is easy to contrast with foliage that is variously lighter, larger, and of a simpler shape. Neighbors of my pair of 'Ruby Lace' include the startling white-and-pink variegated 'Freckles' knotweed, a clump of 'Red Flyer' mallow (whose blooms are actually rosy pink), the white-then-pink flowerheads of 'Pink Diamond' hydrangeas, and the large and even-darker foliage of a pollarded black-leaved catalpa (whose leaves transmit the same rosy-pink light). In June, the trees are backed by a screen of 'New Dawn' roses, whereas in late September, they are flanked by towering clumps of violet-flowered 'Jonesboro Giant' vernonia. To their front, yet another congenial neighbor: The aluminum-white foliage and fragrant white flowers of 'Quicksilver' elaeagnus.

Your priorities may well be for simpler and, overall, lower accompaniments. What about pink- or rose-flowered rhododendrons or azaleas? Oakleaf hydrangeas? Or, simplest of all: Grass.

Where to use it in your garden

I don't recommend allowing 'Ruby Lace' to grow free-range and, therefore, to full size. Then, all its foliage is dull brown by mid-Summer. Instead, grow as a pollard (see the second "How to handle it" box, below), which keeps the tree compact enough to use even in the smallest of sunny gardens. Pollarding requires a yearly pruning in Winter or early Spring; depending on the height you choose, you might need a stepladder to do it. Site 'Ruby Lace' in full sun where you can also have ready access for that easy but necessary project.

Culture

Full sun and almost any soil as long as the drainage is reasonable to good. In cold climates, Gleditsia is famously tolerant of both alkaline and acid pH, exposure to salt spray (from Winter salting or from the seas), and soil that ranges from free-draining and sandy to compacted or clay. In hotter climates, heavy soil can hasten onset of the many ailments that Gleditsia can become afflicted with. See "Downsides," below.

How to handle it: The Basics.

Plant in Spring or Fall, ensuring enough water to establish. Gleditsia is drought-tolerant and established trees need no supplemental irrigation when growing in normally-deep and moisture-retentive soil, and where Summer rain is reliable once or twice a month. Growth of younger trees is faster if trees receive deep watering twice a month during prolonged drought.

If a free-range 'Ruby Lace' is your choice—possibly your garden is celebrating a very sophisticated tan-and-apricot palette?—prune in the Fall as needed, so that the trunk is high enough and crossing limbs are avoided.     

How to handle it: Another option—or two!

Growing 'Ruby Lace' as a pollard is the way to enjoy its foliage at its best. In Fall or in early Spring, cut back all branches to stubs five or six inches long. New shoots bear the more colorful young foliage—and continue to produce it all season or, at least, much more of the season than do branches that are allowed grow on their own year after year.

This pruning also ensures that the spread of the tree's branches is strikingly smaller than when growing free-range, as well as notably more dense. In my experience, the new shoots don't grow extraordinarily long, as can be expected with pollards of, say, Acer negundo, Catalpa, LiriodendronPaulownia tomentosa, or Ulmus glabra. Nor is the foliage of pollarded 'Ruby Lace' trees noticeably larger than that of unpruned branches. But the foliage that is produced throughout the season is pleasing burgundy, and it maintains its youthful coloring longer, too. Pollarding 'Ruby Lace' transforms a sows' ear of a plant into a silk purse, while also creating a tree with a naturally fluffy contour that is also compact overall: An arboreal standard, not just a pollard. Plus, the very compactness of the canopy assists in maintaining the primacy of the colorful new foliage, in that any that does mature to olive-tan is likely to be hidden by the ever-emerging burgundy foliage at the tips of the new stems.

My two 'Ruby Lace' standards are five years old, and were planted as one-gallon starters. They are still very much in their formative years. When their heads of pollarding-induced foliage are more fully formed, I'll post on this cultivar again. 

Quirks and special cases

Gleditsia cultivars are propagated by grafting and, when the ground underneath the trees is cultivated excessively, severed roots (which are those of the thorny, green-leaved species used as the rootstock, not those of the cultivar grafted atop it) can send up shoots. Underplant the tree with durable groundcovers and companion plants so as to make cultivation unnecessary. Gleditsia casts only light shade, so one such groundcover can be lawn. See "Plant partners," above, for others. 

Downsides

Other thornless cultivars of Gleditsia (see "Variants" below) were planted by the millions, lining countless miles of streets and campus quadrangles—and so, of course, all kinds of diseases eventually caught up with them. Plant Gleditsia sparingly; isolated individuals can live long lives below the radar of the bugs, bacteria, and fungal plagues that can demolish mass plantings. Even so, in some locales, Gleditsia is at risk of any number of disfiguring as well as fatal pests and diseases. Check with your local office of the USDA Cooperative Extension Service to see if growing Gleditsia is at all practical where you're gardening. Here in southern New England, the tree is apparently safe.

Variants

I also grow—problem-free, so far—three other cultivars of G. triacanthos: a low weeper, 'Ohio Prostrate'; an upright weeper, 'Emerald Cascade'; and, at full and apparently irrepressible size, 'Sunburst', whose new foliage is butter yellow. Like 'Rubylace', 'Sunburst' can also be grown as a pollard and, then, also produces bright new foliage all season long. A full-sized 'Sunburst' is very showy, but only in Spring and early Summer, which is when its free-range branches are producing their new foliage.

 

For thorn enthusiasts, consider Gleditsia caspica, whose thorns are unique and unprecedented in any hardy tree: Branched fistfuls of six-inch spikes erupt directly from the trunk as well as from major limbs and branches. There's also G. horrida (now renamed G. japonica); it's similarly ferocious.

Availability

On-line and, rarely, at "destination" retailers.

Propagation

By grafting.

Native habitat

Gleditsia triacanthos is native to central North America, from Pennsylvania to Iowa to Texas. Inermis is a naturally-occurring thornless form; inermis means unarmed.

 
 
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