A Gardening Journal

Columnar hornbeams

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What rectangular bed surrounded by paving wouldn't be even more exciting with a quartet of something—anything—emphasizing its corners?  But how tall should those "somethings" be?  Not this tall, that's for sure.

 

Years ago, I'd planted a columnar hornbeam, 'Pinoccheo', at each corner, but then allowed the entire bed to have a Rip van Winkle phase, growing year by year with out any attention. 

 

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But hornbeams don't mind pruning, even at its most radical.  And the trees are so hardy, you can prune whenever you get the yen.  Mid-November?  No problem.

 

'Pinoccheo' wouldn't get much taller or wider ever, but—you know me!—why let something grow on its own if you could prune it?  The big question, then, is "How tall?"  Or rather, how much shorter should the pruned trees be than they are now?

 

The easy answer is that they can't be taller than I can easily reach.  That's an eight-foot step-ladder in the picture below.  If I stand on the second step from the top and prune at my eye level, I'll be cutting off the trees at roughly six-feet-plus-six-feet or twelve feet high.  The tree on the front left is the first to get topped.  And while I'm at it—hornbeams love drastic pruning, remember—why not cut all the side branches back to nubs, too?

 

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Five minutes later, the front pair is completely pruned.  Pruning the back pair won't take but another ten minutes; I'll leave that for another week, when I actually have another ten minutes to spare.

 

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Twenty minutes to resize a quartet of trees for the long term.  And only forty minutes per year (one cut in the Spring, another in the Fall) forever after.

 

Great geometry that's quick to create, and easy to maintain.  No wonder hornbeams are so popular.

 

 

 

Here's how to grow this unusually narrow hornbeam:

Latin Name

Carpinus betulus 'Pinocchio'

Common Name

'Pinoccheo' Hornbeam

Family

Betulaceae, the Birch family.

What kind of plant is it

Deciduous tree.

Hardiness

Zones 4 - 9

Habit

Strongly upright and narrow.

Rate of Growth

Fast.

Size in ten years

Sixteen to twenty feet tall but only four or five feet wide.

Texture

Loose in youth, dense in maturity.  Hornbeams' leaves are comparatively small, and the trees' branching is typically plentiful as well as nicely organized, so there's a lot of foliage.  The fine-grained bulk achieved through countless small leaves on a very branchy structure is similar to that of boxwood.

Grown for

its uniform habit.  Hornbeams don't come in many flavors—see "Variants" below—but all the individuals of a given flavor grow very consistently, one to the other.  Upright hornbeams are usually columnar only in youth, broadening (beautifully) to a wide tear-drop profile in maturity.  Even the so-called columnar hornbeams can be ten feet wide when twenty-five feet tall.  'Pinocchio' is really upright: only half as wide as 'Columnaris'. 

 

its cold tolerance.  Hornbeams are trees for cold climates, or at least climates where there's the certainty of chilly months and real freezes.  They can be planted throughout the Northeast and into Canada, except in the few areas at the highest elevations, which would slide into Zone 3.

 

its solidity.  Hornbeam wood is strong, and the trees are almost never damaged by ice or snow.

 

its amenability.  Like beeches, hornbeams look equally impressive when growing free-range or when pruned into hedges and arches, or pleached into stunning and architectural pollards.  Unlike beeches, hornbeams don't mind occasional drastic pruning.  The hedges are immune to ice and snow-load, and because hornbeams are naturally leafy and twiggy creatures already, they easily prune into supreme density.

Flowering season

Spring, before the leaves emerge.  The flowers aren't showy.

Culture

Full sun and almost any soil provided it's well-drained and doesn't get too dry in the Summer. 

How to handle it

Hornbeams are self-reliant as long as they're sited appropriately.  They achieve a well-tended and year-round dignity all by themselves.  Indeed, if your goal is to have your tree grow free-range, you might not need to attend to it ever again, after ensuring that it's established well its first year. 

 

The narrower cultivars, such as 'Pinocchio' can be left to grow on their own recognizance, too, to achieve their narrower but still smooth and balanced upright form.  Hornbeams' self-reliance, storm-proof structure, and natural density combine with their "prunability" to make them one of the best possible choices for full-size hedges and pollards.

 

It's always safest to plant hornbeams only in the Spring.  If they're grown in containers, they can be planted in the Fall as well.  They can only be transplanted in the Spring.  Balled-and-burlapped hornbeams, which are, in essence, hornbeams that were dug and then held above-ground until their transplanting is completed, should only be planted in the Spring.

 

Hornbeam hedges of almost any height can be created almost instantly—if you can afford it—buy digging a trench and lining up the trees with their rootballs touching.  Prune twice a year thereafter: in Spring before new growth is very far along, and again later in the Fall, to create a crisp outline that lasts through the Winter until growth resumes the following Spring.

 

Hornbeams can also be the cost-conscious choice for hedging—and, truth be told, form better hedges, too—when they're started with the smallest plants that you can find.  Foot-tall youngsters will be great.  Plant them eighteen inches apart and let them grow on their own the first season.  The next Spring, marshall your commitment to growing the best hedge possible, and cut them all down by half.  Your goal is to encourage dense and low-to-the-ground branching, and this is the way to do it.  Then let them grow out the rest of that season.  The third year, cut all the second-year growth down by—you guessed it—half as well.  Let the hedge grow out the rest of the year.

 

From the fourth year on, you have a choice of seasons when pruning.  If you prune in the Fall, the hedge stays sharp all Winter and into early Summer, after which the new growth gives it a shaggier and shaggier profile.  You could, therefore, prune just in mid-Summer, July or early August, say, in which case a second but shorter crop of growth will be inspired.  Most of these leaves will have the unusual talent of remaining attached to the twigs even after they've turned to their Fall color, so the hedge wll be opaque Winter as well as Summer.

 

Then, if you wanted to re-establish strict geometry sooner, you could prune in early Spring, and then again in mid-Summer.

 

Perhaps the least effective choice is to prune only in the Spring.  The hedge will respond quickly with new growth, so you'd only be able to enjoy it at its most cleanly geometric for a few weeks right after pruning.  If you prune only once, do it in the Fall, so the hedge's just-pruned geometry will hold the entire Winter and into Spring. 

 

When you're still encouraging your hedge to reach it's maximum height, only pruning off half of the previous growth.  But when the hedge is the height and width you need, try to cut off all of it. 

 

Even so, hornbeam hedges always seem to find their way to getting a bit too tall as well as too wide.  This is where their comfort with drastic pruning comes in.  One year, cut one side of the hedge back by half in early Spring, which will reduce its thick side branches to to trunk-like stumps.  They resprout quickly, and you can return to their twice-a-year pruning regime the year after.  The next year, do the same for the other side.  And the third year, cut the top foot or two of the hedge right off, so it can regenerate in time as well.  

 

Realistically, you'll probably have three or four years of "garden variety" hedge pruning, followed by three years of "one face / the other face/ and now the top" massacres, during which time you'd continue to prune the non-massacred sides the regular way.

 

Hedges created from small plants are always fuller at the bottom than those created from large plants, which had, almost inevitably, been limbed up a couple of feet when you bought them at the nursery.  That gap never really closes back up no matter how dedicated you are at pruning, either.  Yes, pruning does encourage the trees to branch out, but that low on the trunk what will get encouraged would be the branches right above the trunk, not (usually) new growth directly from the trunk.

 

You could, of course, turn that gap into an asset by interplanting the hornbeams with, say, hostas, which can compete with tree roots and would fill in around the bare trunks, at least during the warm months.  

Downsides

Downsides?  Hornbeams have downsides?

Variants

Carpinus is a small but choice genus.  Its variants are telling, but not nearly as diverse as those of its cousin the European beech, Fagus sylvatica, where new cultivars, each more remarkably diverse then the next, seem to be announced annually.  Hornbeams are a more restrained race.  While everyone respects hornbeams and is proud to grow them, the trees could be thought of as particularly appropriate for gardeners so ascetic in their tastes that even beech trees—themselves the universal standard of propriety—are too diverse, too garish, too busy.

 

In addition to the upright (but tear-drop) and widely-columnar hornbeam cultivars, there's a 'Globosa' that, indeed, becomes almost spherical when mature, but via wide-spreading upright branches, not ones that are directly horizontal. 

 

There's also a weeping hornbeam, C. betulus 'Pendula', which, like its distant relative the weeping beech, matures into a large and stiffly-limbed dome.  I look forward to visiting a couple of the weepers that have been trained out over sturdy metal frames, to create large shady sitting areas.  

 

There are no dwarf hornbeams (yet).  And the 'Purpurea' cultivar retains that color only briefly in the Spring.  Unlike the beeches, there are also no fancy-leaved hornbeams.  The foliage is always oval, coming to a point at the end and with the edges that look as if they've been carefully gone over with pinking shears. 

 

There are a couple of Asian species, C. japonicus and C. orientalis among them.  While they are clearly hornbeams, their subtle differences from C. betulus make them (at least for hornbeam afficionados) irresistible.

 

Perhaps the hornbeam to plant that's most unlike C. betulus is the native C. caroliniana, which tolerates and even prefers some shade, and, uniquely for hornbeams as well as beeches, is very comfortable growing directly by streams and ponds, and even in flood plains.  It is typically multi-trunked, and with smooth sinuous trunks with "tightly-applied" bark that suggests one of the common names, "muscle wood."  Another of the common names, "water beech," emphasizes the species' unique comfort with wet soil.   

Availability

I got my 'Pinocchio' at Broken Arrow Nursery some years ago; I don't see it listed there or elsewhere, but another columnar cultivar, 'Frans Fontaine', is very similar.

Propagation

By grafting. 

Native habitat

Carpinus betulus is native to the British Isles. 

 
 
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