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

Tree Caragana

caragana-arborescens-091612-cropped-640

 

Blue-green foliage that's interesting only if you've never seen better.  Yellow flowers that are pleasant but quick.  At first glance, tree caragana seems like a why-bother.  But the shrub has so many other talents that the real question should always be "Why not?"

 

The shrub has such potential that it's going to replace much of an allée of lindens, mysteriously failing, that were supposed to have structured my garden's ultimate destination: An enormous yellow-border-to-be, at the right, and an enormous reflecting pool, hidden behind its horticulture at the left.   That's a linden stump right in back of the little whip of Caragana arborescens

 

caragana-arborescens-091612-640

 

Tree caragana will thrive in sun and almost any soil that isn't sopping.  It grows quickly.  But these two gifts are the clincher:  Its young twigs are green, and it can be trained into a pollard.  Pollarding means an annual prune-off of nearly all of the previous year's canopy of branches—which, all too conveniently, encourages the maximum growth of a new crop of green-barked twigs..

 

Caragana arborescens grows so quickly there's no need to plant other than a starter size, and will replace eight of the allée lindens:  One quartet to the reflecting pool, one quartet to the east  The central four lindens have already been replaced with a tree that is, if anything, even less often seen in such a hypergeometric context:  Osage orange.  Stay tuned.

 

Here's how to grow this unusual and oh-so-hardy tree:

 

Latin Name

Caragana arborescens 

Common Name

Tree caragana

Family

Fabaceae, the Pea family.

What kind of plant is it?

Deciduous shrub that can be trained as a small tree.

Hardiness

Zones 2 - 7.

Habit

Growing free-range, a large, upright, rounded, multi-stemmed beast.  Can become open at the base.  With knowledgeable pruning—see below!—the species can be transformed into a lower and wide-spreading shrub, or into a round-headed standard.

Rate of Growth

Fast. 

Size in ten years

Caragana arborescens is usually fast-growing, and can be expected to grow to 15' to 20' tall and 12' to 18' wide in a decade. 

Texture

The pinnate foliage is feathery, but not nearly as dissected as that of the cut-leaf form of tree caragana, C. arborescens 'Walker'.

Grown for

its toughness.  Caragana species are renowned for their tolerance of poor soil, drought, salt (both salt-spray and salty soils), wind, and intense cold.  As is typical for Caragana species, C. arborescens fixes nitrogen, so is self-fertilizing.

 

its appeal to wildlife.  The seeds are eagerly sought by birds; the shrub is so prolific and wide-spread in cold climates that the pods can be harvested as chicken feed.  In literally Arctic habitats, the shrub is reportedly a welcome fodder for reindeer; finally, I've got that base covered.  When green, the seedpods can be eaten as a vegetable.   

 

its young twigs, which are grasshopper green.  Most trees and shrubs whose young twigs are colorful—see these examples of Siberian dogwood, maple, linden, and willow—maintain that color only for the first year, with the bark of older growth noticeably less colorful, and usually tan.  Twigs of tree caragana remain youthfully green for several years.

 

its hardiness.  Zone 2:  Even Minnesota isn't cold enough to challenge this shrub's hardiness; to garden in Zone 2, you'd need to drive from Minnesota northward into Manitoba for a day.  Take a lot of Caragana with you.

Flowering season

Late Spring, emerging with the foliage.  The yellow flowers are narrow and tubular, and are showiest at close range.

Color combinations

The yellow flowers are ephemeral and subtle, so Caragana arborescens can be sited more on the basis of its blue-green foliage and mid-green young twigs, which go with everything. 

Partner Plants

Free-range Caragana arborescens is almost too dense and large, as well as not sufficiently ornamental, to consider for plant partnerships that are aesthetically driven.  But when the shrub is coppiced (see "How to handle it: Another option—or two!") or pollarded (see "Quirks and special cases"), it is eminently compatible with plants that also appreciate its preferences for full sun and full exposure, and well as its indifference to soil moisture or richness.  

 

Because the yellow flowers are fleeting, and in such small clusters that they aren't readily discernible against the foliage, warm-weather pairings are best guided by the plant's foliage as well as its training as a shrub (by coppicing), or as a small tree (by pollarding).  I yearn to underplant a pollarded tree caragana with Yucca filamentosa, whose swords of evergreen foliage and dense clumping habit would provide a weighty and similarly tough ballast to the pollard's canopy of ferny foliage.  As long as the bottom of the pollard's head were higher than six feet, the yucca's tall spikes of June flowers would be an arresting mid-level show, not a bizarre poke-into-the-armpits conflict.  In Winter, the display of yucca foliage is unabated, and could continue its lively conversation with the pollard's twigs; they would then be leafless but, thanks to their bark, still green.

 

In Zone 5 and warmer, consider clothing the trunk of a pollarded tree caragana with an evergreen self-clinging climber such as Hedera colchica, Hedera helix, or Euonymus fortunei.  All come in variegated cultivars whose bright coloring would be as interesting a contrast with the pollard's green Winter twigs as its blue-green Summer foliage.  If you clothe the entire trunk right up to the pollarded head, you've given your pollard a sleeve or sheath of greenery.  If only half-way up, you could call it a legging.  If only for a foot or two, a spat.  Pollarded trees with spats:  Truly, one of the ultimates in defiant garden artifice.  If all goes as planned, my garden will have eight spatted tree caraganas.  Oh, yes!

 

Who knows, but you might have need of pollarded tree caraganas in tight formation.  An entire grid of them, even, to go toe-to-toe with a long, long wall of a modernist building.  If you plant them in decent soil, you could underplant with hostas, whose thick round leaves would thrive in the dappled shade and, at Zone 3, nearly the same exceptional hardiness.  I'd plant the pollards six feet apart, in staggered rows.  The Winter-time density of the pollard's aggregate green twigs would be remarkable.  Ah, for a client with a corporate headquarters in Nome or Ottawa.  

 

Coppiced individuals of Caragana arborescens will be rounded, broad, and self-supporting.  Growth will be too close to the ground to underplant with anything taller than a groundcover that will thrive in the same well-drained conditions as the now-shrubby tree caragana—but also in its close-overhead shade.  Shade and drought tolerant—and a welcome contrast to the small caragana leaflets?  What about Geranium macrorrhizum, literally "big-root" geranium?  Its fuzzy rounded leaves are dead ringers for those of Alchemilla mollis; it also thrives in shade, but tolerates much drier soil than the Alchemilla.  As long as your shady soil isn't lean as well as prone to drought, epimediums are another possibility.  If you're gardening in Zone 7, you're at the upper limit of the heat tolerance of Caragana arborescens.  Try pairing with Euphorbia robbiae, a shade-tolerant broad-leaved succulent groundcover that, in Zone 7, is at the cold end of its hardiness.  The pairing would be a marriage every bit as mixed as having one spouse from Jamaica and the other from Quebec.

Where to use it in your garden

If allowed to grow free-range, tree caragana is both too large and not sufficiently ornamental to use in the garden proper.  It is terrific as part of a background screening, for a large-scale tough-as-nails windbreak even in the most exposed and brutally-cold sites, and as habitat, food, and shelter for wildlife.

 

See "How to handle it: Another option—or two!" and "Quirks and special cases" below for pruning options that enhance its ornamental appeal while also reducing its size.  So transformed, Caragana arborescens can be a stylish as well as rarely-used element of even the most fastidious and tightly-organized garden.

Culture

Full sun and almost any soil and habitat that's neither waterlogged nor desperately dry.  As with Syringa, another supremely hardy genus, Caragana species have no interest in being sheltered or shaded.  The shrubs revel in the unsparing full-sun exposure that would either demolish from wind pressure almost anything other than birches, or freeze them to the ground.

How to handle it:  The Basics

Plant in Spring or Fall—or, indeed, during Winter if the soil is workable.  Water at the time of planting, but the shrub is so tough and tolerant that you don't need to worry about it thereafter.

 

If you're planting tree caragana as part of a large-scale windbreak, you're done as long as you keep other nearby plants from growing large enough to cast the caragana into shade.  By the same token, keep the caragana free of volunteer vines, shrubs, and trees—where I garden, this includes such opportunistic tediums as bittersweet, multiflora rose, autumn olive, Norway maples, and poison ivy—lest they grow large enough to shade it out.  

How to handle it: Another option—or two?

Caragana arborescens could be pruned into an informal hedge, but there are other candidates for hedges that are nearly as hardy and accept pruning much better—privet if you must, but what about American beech?—that tree caragana is better left to a naturalistic profile.

 

You could, however, coppice the shrub every two or three years, which keeps it notably more compact, and also removes stems that have become old enough to lose their green bark.  Although the flowers are only modestly showy, you could show respect for them by delaying your pruning until they are through.  This delay would also reduce the overall height of the resultant regrowth, because its growing season would be a few weeks shorter.  On the other hand, if you find that Caragana arborescens self-seeds where you're gardening, or that somewhat larger-size regrowth isn't a problem, or if your growing season was so short that you'd be happy for the largest regrowth possible, you could coppice in late Winter or early Spring.  This cuts off the stems that had, the Fall before, formed all the buds that were going to open in May.   No flowers, no seeds, no self-seeding.

Quirks or special cases

The young twigs of C. arborescens stay green for several years; the shrub grows tall enough to form trunk-like lower limbs; and the shrub regrows quickly, even when heavily pruned.  Take advantage of all three qualities by training the shrub into a small tree whose branches, thanks to annual pollarding, are fresh green all Winter.

 

First establish the shrub and let it grow free-range for a year.  Then select a central stem that's already reasonably vertical, cut away all the other stems, and lightly stake the remaining stem so it can grow with true verticality.  It will become the trunk of your tree caragana.  Let the young tree grow free-range for a few years, including side branches that emerge from the young trunk.  Prune off stems that originate from the base of the trunk or directly from the roots. 

 

Let the top of the trunk grow to about eight feet tall and, the next Spring, prune as follows:  Cut off the lower branches to reveal the trunk up to about six feet, cut back the remaining branches to two or three inches, and cut a few inches from the top of the stem that is the vertical tip of the trunk.  The stubs will send out side branches, so the canopy of your small tree will begin to take shape.  Some of the branches you pruned away entirely to reveal the tree's trunk will probably sprout new growth, too.  Prune those sprouts away whenever it's convenient to do so.

 

Let the tree grow the rest of the season.  Each Spring thereafter, prune back all the canopy's branches to stubs right after flowering.  Remove any lower growth at any time.   

 

Your tree caragana will soon form a dense but casual head of wand-like branches that, after frosty weather removes their leaves, will show off their lovely green bark all through the cold months. 

Downsides

Caragana arborescens is only appropriate for smaller gardens if you've committed to the annual pollarding or coppicing.  This is not a free-range shrub for any landscape other than those that are large, and even then, only in situations where self-reliance is imperative, wildlife habitat is desirable, and naturalistic shelter-belt plantings are the aesthetic style and functional goal.

Variants

There are scores of Caragana species, all native to Europe and Asia.  With the exception of a couple of feathery-leaved cultivars ('Walker' and 'Lorgergii'), and dwarf or pendulous cultivars ('Nana' and C. pygmaea, 'Walker' as well, and 'Pendula'), most are upright and broad shrubs that are terrific more for strictly functional uses (e.g., as large-scale groundcovers, as wildlife habitat and food, as nitrogen-fixing soil amenders, as part of a shelter-belt in unusually cold climates) than as garden ornamentals. 

Availability

On-line.

Propagation

By cuttings and by seed.

Native habitat

Caragana arborescens is native to eastern Siberia and Manchuria.

 

 
 
FacebookTwitterRSS Feed

Stay in touch!

 

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

 

* indicates required