A Gardening Journal
Today in the Garden of a Lifetime: The Mysterious Volunteer Mulberry
- Published: August 22 2016
For brilliant gold foliage that stays bright all Summer, the aureate forms of Scots elm and paper mulberry are unsurpassable. The mulberry adds unusually shaped foliage, each leaf of which is is mitten-like and variable: Sometimes there's one thumb (and on either side), sometimes two, and sometimes none.
Below, a gold-leaved paper mulberry that is unusual thrice over: First, it isn't my original mulberry, which is about eighteen feet away. And yet, here it is, sprouting up through the wide joints between the terrace's dry-laid slabs.
Second, its leaves almost always have an additional pair of lobes at the bottom. Leaves of my original mulberry have three at the most, looking like one or two thumbs on either side of the central hand. These leaves regularly have five lobes, not to mention a distinct serrated edge. Further, the lobes are much more deeply incised. Very showy!
Below, my original Broussonetia papyrifera 'Golden Shadow'. You can see leaves with two, one, or no thumbs—I mean lobes—but none with five.
Third: What could be the relationship between this established paper mulberry and the five-lobed volunteer? There are just two possibilities. Broussonetia isn't native and isn't naturalized locally—and even if it were, spread by seed isn't likely. The species is dioecious, and both male and female plants are needed for the females to set seed. 'Golden Shadow' is a male, and it's the only form of Broussonetia I grow. Even if there were a female in the neighborhood, that would be acres distant, so volunteers would most likely appear near her.
Plus, this foliage is every bit as aureate as that of my 'Golden Shadow'. It would be highly unusual for coloring to persist to this intensity in seed-grown offspring, and especially considering that any female in the neighborhood would be green-leaved. (Otherwise, I'd have spotted her.) Further, to my knowledge, there are no aureate forms of paper mulberry that are female.
The only other possibility seems remote, too: that this flashy foliaged youngster is sprouting from the roots of my 'Golden Shadow'. Although it's about eighteen feet away and I've never seen other sprouts, this is almost certainly this volunteer's origin. Trees often send out roots farther than their canopies' above-ground spread, and Broussonetia papyrifera is famous for suckering.
I planted my 'Golden Shadow' six years ago, and it is so well established that it thrives with a ruthless Spring pollarding. Such pollarding can remove the growth inhibition that upper stems often force onto lower; the result can be greater-than-usual sprouts from lower down or, even, from the roots. But I've never been aware of any other root sprouts from this tree. It's weird, indeed, that just this one would emerge, and from a root that had extended so far away. If pollarding did encourage root sprouts from my 'Golden Shadow', I'd have expected a lot of them, not just this one, and all much closer to the trunk.
Lastly, this sprout's delightfully detailed leaves. Are their serrated edges, pairs of additional lobes, and deeper-than-usual incising of those lobes typical of root sprouts of the species? Root sprouts just of 'Golden Shadow'? Just this root sprout of this 'Golden Shadow'? With just one such sprout to date, it isn't possible to conclude. Paper mulberry is established at the Arnold Arboretum, though. Perhaps that tree has developed root sprouts. I will be in Boston later in September, and I'll try to visit it.
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 interesting this tree's bark is in Winter, as well as how to maximize its cool-season display.