A Gardening Journal
Today in the Garden of a Lifetime: Colorful Bark of the Paper Mulberry
- Published: January 01 2016
The yellow foliage of 'Golden Shadow' paper mulberry doesn't fade or scorch even over a long hot Summer. (The only other hardy tree that can make the same claim is the 'Aurea' form of the Scots elm.) It's no surprise, then, that nurseries and even references rave only about the mulberry's leaves. Before today, I was as guilty: I had written about this tree three times—but each time largely about its foliage. See the links, below.
Then, I finally noticed the tree's marvelous Winter bark. The new stems are as colorful as the trunk, and each in its own way. Take a look at the first-year stems, below, whose bark is pale green.
The tree's trunk—its oldest growth—is just inches below these green stems that are just months old, and its bark is much different. What a dramatic overlay of snaky bright-cinnamon striations it has developed.
It isn't uncommon for a tree's youngest twigs to be colorful, but it's unusual indeed for a tree's oldest stem—its trunk—to be equally showy. And yet I'm having difficulty locating any write-up of Broussonetia papyrifera 'Golden Shadow' that looks beyond the admittedly fabulous leaves.
This bi-level show—colorful stems up top, differently colorful trunk immediately below—is similar to that of my curly-leaved willow, but only because it is pollarded. Perhaps that is the key. When trees grow free-range, the very youngest twigs are at the ends of the branches—and those branches are usually long and their bark is usually several years old. Those young twigs aren't just high above ground, they are also distributed through a large volume of space by those bulky and lengthy mature branches whose bark may well be comparatively bland.
Similarly, the trunk is at equal distance from those young twigs, making any contrast between the two harder to discern. By pollarding, I cut off branches before their bark becomes old enough to be boring. This same act also encourages new stems to emerge almost directly from the upper reaches of the trunk, creating the strongest possible juxtaposition of the two. Plus, the growth of these resultant stems is often more colorful (in leaf or bark or both) than that of stems emerging from unpruned branches.
The display of pollarded trees, then, has been intensified many ways compared to that of free-range ones: Boring older growth is removed, new growth is formed more densely and at an easy viewing range, the contrast between the new growth and the permanent lower trunk or major branches is maximized, and the overall look of the tree is changed from a natural irregular shape to a clearly-intentional specific shape. Further, these changes don't just add up independently of each other: The removal of the older growth itself causes a more profuse emergence of new growth (and within a much smaller volume) that is (often) showier than that formed when the tree is left to itself, and that gives the overall tree a simple ball-atop-a-stick shape that is inherently more striking than its more complicated free-range shape. Happily, these consequences of pollarding are also mutually enhancing. They synergize instead of conflict.
While there's always pleasure in discovering that one of your garden's plants is even more interesting than you had been led to believe by catalogues and references, there's sometimes frustration. If I had realized that a pollard of 'Golden Shadow' mulberry wasn't just smaller than the free-range tree, it was also a Winter show of twigs and trunk, I might have sited the tree where a higher trunk would have been an asset. In its current spot, the trunk is just two or three feet because the need was only for a five- or six-foot mound of fantastic gold foliage May through mid-October. I hadn't realized that there was any show from November through April.
As a garden designer, my own garden is one of many—scores and scores, even—that I'll have created over my professional lifetime. There isn't room for higher-trunked pollards of 'Golden Shadow' mulberry in my own garden, but perhaps there will be the opportunity in a client project. Or for you to develop in your own garden.
One of the many satisfactions of "growing" LouisThePlantGeek.com is that I identify all kinds of ultimate and in-my-dreams combinations and layouts that would showcase this given plant handled this particular way while partnered with those other plants, and all in such a knowing and theatrical array and setting. There will never be time, space, or money for me to realize them all. But, over the long term, if some of you were able to create just a few of my "ultimates" while also dreaming up and then creating some of your own? What amazing gardens we'll have brought to life.
Here's the introduction on how to grow this glorious golden tree.
Here's a closer look at this tree's shape-shifting foliage. The leaves it produces in Spring have one shape; those produced in Summer, quite another.
Here's how particularly interesting this tree is in Spring, when the ephemeral bronze color of the new foliage matches that of the catkins.
Here's how to grow this tree to maximize its cool-season display of bark:
How to handle it: Another option—or two!
As is typical for fast-growing woody plants, Broussonetia papyrifera can be cut back severely, and will resprout enthusiastically. This pruning can, of course, dramatically reduce the tree's size while maintaining that now-compact scale for the long-term. It also stimulates production of plenty of fast-growing new stems with showy pale-green bark. The leaves of these extra-vigorous shoots are also reported to be much more likely to be lobed, whereas foliage on stems that have not been pruned is much more likely not to be lobed. Lobed foliage is more interesting and, so, this is yet a third reason to consider a radical annual pruning.
As with another fast-growing tree, the white-stemmed poplar, so much sap is produced as the mulberry gets going in Spring that pruning then—or even soon before—creates a mess: That sap drips readily from the cut stems. Instead, prune in early to mid-Winter, when weather is still severe and the tree is, therefore, still dormant. This means that, yes, the cool-weather display of colorful young twigs can't be retained all the way through to Spring. Think of the show as you would that of any Spring flowering tree: a remarkable but also ephemerical peak that should be enjoyed in the moment.
Pollarding early in Winter removes only the previous season's growth; the tree's trunk itself stays untouched year after year. The Winter show of a mulberry pollard, then, is first two-fold—twigs atop the trunk—and then unitary: just the trunk. This is all the more reason to develop a pollard whose trunk is as tall as is practical.
Let the young tree grow ad libitum for two or three years, so it can build up a head of steam. Then, in mid-Winter, select the most central and straight stem and, as needed, stake it so it is truly vertical. As it develops as the tree's trunk, the snaky vertical striations of its bark will become increasingly showy. Allow it to grow to at least six to eight feet high—or even to ten or twelve if you're comfortable using an eight- or ten-foot stepladder to raise yourself high enough to do the pollarding. The next Winter, clip off whatever of the young trunk's tip is already higher than your target trunk height. Clip or saw off all other branches, too, leaving just this central, vertical trunk-in-training.
Allow side branches to form all over this "trunkette" that Spring and Summer. Each mid-Winter to follow, prune off entirely any that arise from the lower portions of the trunk. At the same time, shorten back to stubs just a couple of inches long stems arising from the upper foot or so of the trunk; you'll have left in place plenty of side buds from which new stems in Spring and Summer can emerge. In just a few seasons, the trunk will have thickened and can be released from its staking; it will also be producing a full head of new stems each season. Some of these stems are likely to grow six feet long; a thriving Broussonetia pollard, then, might have a canopy that is six to twelve feet in diameter. Allow plenty of room in considering where to establish the young tree.