Plant Profiles

Lavender-twigged box elder

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What odd twigs!  They're covered in a an icy-pale bloom, which rubs right off on my fingers. 

 

Put a lot of the twigs together, and effect just gets weirder.  The icy color is, now and clearly, lavender

 

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Weirder still, I had to saw off all of these branches and stack them on the grass before their color became clear.

 

This view shows the mid-section of the branches.  The lavender bloom is only on the new twigs.

 

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There's no interesting color at all to the base of the sawn-off branches.

 

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Before I sawed off the last branch, I looked at it against the sky.  No color visible from this vantage, either.

 

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What a challenge: A tree that looks best when it's branches have been cut down.  Is there hope?  See "How to handle it" below for my best strategies. 

 

As further enticement to give this tree a try, the early-Spring flowers are pink-purple, with astounding stamens several inches long.  Indeed, because the flowers don't have petals, it's the stamens themselves that are providing all of the pink-purple.  For a time, the entire tree looks festooned with cheerleader pompoms. 

 

Here's how to grow this unusual maple:


Latin Name

Acer negundo 'Violaceum'

Common Name

Lavender-twigged box elder

Family

Sapindaceae, the Soapberry family.  Synonym: Aceraceae, the Maple family.

What kind of plant is it?

Deciduous tree.

Hardiness

Zones 3 - 9.

Habit

Single-trunked and broadly upright.

Rate of Growth

Very fast. 

Size in ten years

Twenty to thirty feet tall, twenty wide; ultimately over forty feet tall.  Spring pruning is recommended, which will reduce the size considerably. See "How to handle it" below.

Texture

Lively in leaf, thanks to the somewhat unusual three- or five-leaflet leaves.  The bare branches can be gawky if the tree isn't pruned for greater compactness. 

Grown for

its unusual young stems, which have a grey-lavender bloom that can be showy in Winter through early Spring, when the tree is leafless. 

 

its female flowers; Acer negundo is dioecious, and 'Violaceum' is a female.  Its apetalous flowers are in dense pendulous racemes, and have startling long lavender-purple stamens that are, themselves, pendulous—to several inches!

 

its imperviousness to deer:  In my experience, box elders are not appealing to herbavores.  Hooray!

 

its comfort in truly cold climates:  Being hardy to Zone 3 means that box elder could handle the sub-arctic Winters in deep northwoods Quebec, far away from the St. Laurence River, which moderates Winter's worst along its banks to "only" thirty below zero.

Flowering season

Early Spring, before the leaves emerge.

Color combinations

'Violaceum' adds its colorful displays of twigs and flowers only to the cold months, so take care that 'Violaceum' isn't within earshot of other cool-weather displays that are trumpeting yellow or red.  Alas, yellow is the color of so many cold-weather and early-Spring flowerers—witch hazel, corylopsis, mahonia, Cornelian cherry, forsythia, Winter aconite, daffodils—and it would be a bilious combination with the peculiar grey-lavender hue of 'Violaceum'.  Even white partners could be difficult, making the 'Violaceum' twigs look dull or even dirty.  And this rules out another large group of plants with Winter interest, including snowdrops, some hellebores, fragrant honeysuckle, and early and white cultivars of magnolia and cherry.  Lastly, the grey-lavender twigs are liable to make any cream-colored partners look uncomfortably yellow.

 

Green, purple, blue, and pink are the natural colleagues for 'Violaceum'.

Partner Plants


In warm weather, 'Violaceum' is in leaf, and brings a mid-green presence in the garden.  Neutral, in other words, so the tree can be the warm-weather backdrop to any other color.  But the Winter and Spring shows are so specifically pink-friendly, and at a time when there isn't much other pink-friendly horticulture to be had, that 'Violaceum' can be somewhat of a puzzle to work into a color-coordinated cold-weather planting.

 

Would 'Violaceum' be in bloom the same time as early pink-flowered cultivars of magnolia or cherry?  It would be the perfect shade-provider to your largest collection ever of pink, rose, purple, and "black" hellebores.

 

If, by a miracle, you've chosen to plant 'Violaceum' near an area, or at least a container, that you cycled through the year with seasonal plantings, then you could stock it for the Winter with pink or purple-leaved kales.  In this case, you'll want to grow the 'Violaceum' as a bush not a tree, so its twigs are near enough to the kales for the color harmony to take effect.  See "How to handle it" below for strategies. 

 

The most numerous partners—and possibly the easiest—are those whose function is to supply a neutral evergreen backdrop for the display of twigs and flowers.  Holly, bamboo, Southern magnolia, say.  The taller you let 'Violaceum' grow, the taller and bulkier that backdrop needs to be. 

 

If you pollard your 'Violaceum', you could grow ivy or euonymus up the trunk.  Safest would be all-green varieties, from which the cold and pale 'Violaceum' twigs would erupt.  In case that's still not enough cleverness, perhaps there are varieties of ivy or euonymus whose foliage pinks up for the Winter.

 

If you coppice your 'Violaceum', you could underplant it with one of the usual evergreen groundcovers—vinca, pachysandra, or prostrate Cephalotaxus—against which its bizarre Winter twigs would show beautifully.

 

In the Summer, when 'Violaceum' is a mid-green backdrop, it could host the display of a climber of any color.  The trick is to choose one that also needs to be pollarded in Spring along with the 'Violaceum' and grows quickly enough in response so that its growth, and therefore its colorful display, can stay near the tips of the fast-expanding canopy of 'Violaceum' twigs.  They can become eight feet long or more by September, so any "partner-pollard" vine would need to grow fast, indeed.  No roses qualify, but perhaps cultivars of Clematis viticella would; they can grow twelve feet by September when cut down to a foot in the Spring.  Would they grow that same twelve feet if only cut back to the height of the pollard trunk?  There's always Autumn clematis, C. maximowicziana, which could rampage to fifteen feet or more each season.    

Where to use it in your garden

Acer negundo 'Violaceum' is a true eccentric, and in a season when so much of the rest of the garden is in full retreat, or even full disarray.  As with all exceptional plants, this one can't make up for deficiencies in the garden around it, so siting it as I myself have done—amid plants that have packed it in for the Winter—is somewhat of a waste.  Instead, consider a special area where this plant's unique coloring and cold-weather peaks can be sheltered from the comparative dullness and entropy of the rest of the Winter garden.  The evergreens that are the best backdrop for 'Violaceum' are also the best way to ensure this tree's visual privacy.

Culture

Full sun and almost any soil, even those that are squishy in Winter.  Acer negundo is often found stream-side and even swamp-side, so it has no fear of wet feet.

How to handle it:  The Basics

In my experience, the Winter twigs of 'Violaceum' don't color very well when the tree grows free-range.  Fortunately, box elders respond eagerly when pruned, growing masses of new twigs that color to the max.  Your choice is in growing 'Violaceum' as a large shrub, in which case you'd prune all the twigs back to the main stump, or as a small tree, in which case you'd prune all the twigs back to the top of a short trunk.

 

I recommend the shrub option.  The resultant twigs will still grow to six, eight, or even ten feet, but they'd be much closer to the ground—and to you, their Winter witness—than they'd be when growing from the top of a trunk that was itself six, eight, or ten feet tall.  Coppice the tree—in other words, cut all branches back to short stubs—each Spring as soon as the flowers have finished.  If you've partnered 'Violaceum' with a late-Summer climber, cut that back at the same time. 

How to handle it: Another option—or two?


If you'd like to grow 'Violaceum' as a small tree, prune all branches back to the top of a short trunk; six feet is plenty high enough.  Prune after the flowers have finished.  If you've partnered 'Violaceum' with a late-Summer climber, cut that back at the same time, but only as low as the trunk of the 'Violaceum'.  It's best to grow the "partner pollard" up its own stake, not up the 'Violaceum' trunk, so that it's planted far enough out from the tree that it will escape most of the competition from the tree's roots.  Planting a partner-pollard five feet out would be the minimum distance.  'Violaceum' twigs grow so fast that you'll have little difficulty ensuring that the vining growth of the partner-pollard can latch onto new growth of 'Violaceum', which will extend within reach by June or certainly by early July.

Quirks or special cases


None.

Downsides

Acer negundo is not long-lived in the American South, or any similarly hot-and-humid climate, where it is particularly susceptible to a fatal canker.  The tree is one of the hosts of the eponymus boxelder bug, which can migrate into houses to overwinter.

Variants

Given that the species itself is widely considered a weed, and often tops "Please, cut this down first" lists, it's surprising how thrilling and helpful so many of the cultivars are.  Colorful foliage is the main theme.  That of 'Kelly's Gold' is chrome yellow; of 'Flamingo', white and pink; of 'Aureo-marginatum', green and bordered in yellow; of 'Variegatum', irregularly white-sectioned.  Some cultivars, such as 'Violaceum', also have showy Winter twigs.  Those of 'Kelly's Gold' and 'Winter Lightning' are yellow; of 'Flamingo', pink then green.  I'm only aware that 'Violaceum' also has colorful flowers. 

 

The habits and sizes of all Acer negundo cultivars are similar; to date, there are no truly dwarf, prostrate, or weeping variants.   

Availability

On-line.

Propagation

By cuttings, which root easily.

Native habitat

Acer negundo is native to North America, from Canada to Mexico, and almost the entire continental United States.