A Gardening Journal
Fabulous in the Fall: Weeping Dwarf Siberian Elm
- Published: December 04 2016
Gardens are the result of countless choices made day by day and decade by decade. Which plants? How to handle them? What layout of beds, pathways, and grass? When to switch to Plans B, C, and D?
The weeping habit of this unnamed cultivar of dwarf weeping Siberian elm is so intense that I couldn't resist growing it. Left to themselves, its branches stream downward with jagged irregularity. Because Ulmus pumila is native to Siberia and northern China, the tree is so hardy—climate zone 4—that it is a candidate for growing year-round in a permanent container here in southern New England, which is nearly zone 7.
Why in a container, although not this cracked black nursery pot, to be sure? Then I could give this cascading cultivar's tumbling branches free range by placing it on a pedestal early spring to late fall. In the picture below, the pot is actually resting on its side, with the top of one of the stone tables as a backdrop. The branches have already cascaded downward twice the height of the pot or more; if the pot were placed upright, the branches would first have had to have been splayed outward.
The branches' extreme degree of natural cascade means that, if grown in the garden on level ground, this tree would be a groundcover. Perhaps branches would root where they touched the soil, forming a dense mounding colony that, over time, could spread indefinitely.
But all forms of Ulmus pumila can be nearly defoliated during the summer by the elm-leaf beetie. Plus, the brittle wood of the full-sized forms is susceptible to ice and wind damage. Siberan elm is now near the top of most Do Not Plant lists, and it would be foolhardy to give one a permanent space in the garden. Such well-deserved unpopularity might mean that Siberian elm, once planted widely as a survives-anywhere solution, is now mercifully scarce in my locality.
The leaf beetle isn't in evidence, either: none of my other ornamental elms—Ulmus glabra 'Aurea', Ulmus x hollandica 'Jaqueline Hillier', and Ulmus x hollandica 'Wredii'—has ever suffered defoliation. Further, in the year I've grown this dwarf weeping form of Ulmus pumila, its foliage has remained pristine. See the undamaged leaves in the third-down picture of the profile of Leycesteria formosa 'Golden Lanterns'.
Growing this bizarre and small-scale Siberian elm in a container, then, is a big adventure but only a small risk: if the leaf-destroying bugs do find it, I could move the container out of sight by late summer. I'd bring it back into view in late fall, when the display of bare branches would be particularly dramatic. And because I'll be training the tree so that it's always diminutive—I can't be lugging a twenty-gallon pot around the garden too often!—if it ultimately succumbs, the garden's loss will be of one out of a thousand details, not a major feature.
The overall habit of any plant that is weeping, especially as tortuously as this one, is going to be its calling card: what one notices first. But a dwarf weeping Siberian elm has other charms that, happily, the compact cascading habit calls attention to. The picture below highlights one of the fast-growing stems that emerged this spring near the base of one of the little tree's trunks. Its buds are nearly two inches apart, which is quite a distance for a tree that is dwarf: plants are dwarf, partly, because their growth is more congested than usual. For a plant, congestion means that there is a shorter than normal distance from one bud to the next. While this stem's habit is still cascading—its vigor doesn't mean that it also grows upright—its length of nearly two feet would classify it as one of the tree's waterspouts, the term for just such "mile a minute" stems.
Look at the section of the branch shown below. Its buds are only a third as far apart as those of the waterspout, and they are round, not pointed. This stem emerged from an older branch, not directly from the trunk; you can see its point of origin just above the tip of my index finger.
Held side by side, the difference in the two stems is dramatic.
The stem on the left—the waterspout—is vegetative. It will continue to lengthen next season, and side-stems will emerge from its little pointed buds. The round buds on the stem on the right are flowerbuds; flowering stems emerge from older stems, not directly from the trunk. As is typical for elms, flowers of Ulmus pumila are out before the foliage in early spring and, so, need to be partially formed the fall before. These fall-formed buds are showy—and all winter long.
Flowers won't appear on the full length of this stem. Below is almost all of it, and you can see that just the portion that was formed earliest in the season—that is, closest to its point of emergence from last year's growth—is bearing flower buds. I count eight of them. The distance between buds gradually increases, and then—whether because there was a stronger imperative to switch to vegetative growth later in the season, or because further flower buds can only be produced when the distance to the adjacent flowerbud is within some limit—the buds change. Buds nine and ten seem intermediate: sort of flowerbuddy but not as round, but rounder and more projecting than the vegetative buds farther down. These were formed more towards the stem's tip, which means much later in the growing season.
Perhaps flowerbuds are more time-consuming to form than vegetative ones, and by, say, August, there isn't enough growing season left to continue to make a commitment to their formation. It's not that the tree would "know" the date, let alone how much growing season would remain in a climate with a growing season much longer than that of its native Siberia. Rather, the rate and type of growth may well be affected by the changing proportion of the lengths of the days versus that of the nights. Once the days become short enough, a hormonal change might happen that switches off formation of flowering buds in favor of the default, the vegetative ones.
I'll tie a section of green horticultural wire between buds eight and nine, so we can see just what flowers and foliage develop there come spring. The flowers are fluffy red-and-plum heads whose display is largely lost on full-sized trees, where flowering stems can be ten to fifty feet overhead. On a dwarf weeper such as this one, every flowerhead will be, literally, right at hand.
I'll revisit Ulmus pumila "Dwarf Weeper" in 2017, both to show the flowers and also the start of the tree's training into a more full-skirted cascade. I'll provide the full Here's How To Grow It table then, too.