After last week’s post about peach-leaf bellflower, I got to thinking about all the other plants with spreading tendencies that inhabit my small urban garden (50 x 120 feet, including my house, garden shed, garage, driveway and various walks and paths). Quite frankly, I was appalled when I realized how many pushy plants I have. No wonder there’s no room for anything new.
So I thought I would compile a list of them — trees, shrubs, climbers and herbaceous plants that spread by running roots, offsets or suckers. The list doesn’t include “true” weeds (bindweed, for example), but does have plants that are probably considered weeds by some. Enough said.
Trees: the only invasive one I have is the Tree of Heaven, Ailanthus altissima, which sends up shoots here and there. Digging them out, I find that they originate in structures that look like brains, except they are a yellowish colour. Very sinister. If not removed, the shoots will grow into more trees, and I would have a grove of what has been called “the world’s toughest urban tree.” Indeed, but one is more than enough for me.
The common Lilac, Syringa vulgaris, sends up suckers with abandon. I remove them, so as not to end up with a lilac thicket that swamps whatever has been planted around the shrub. I suspect that named varieties are less apt to sucker, but are probably not as tough. Besides, this lilac was here before I arrived in 1992, so has the privilege of seniority.
Oregon Grape (Mahonia aquifolium) is a native shrub that can grow to 10 feet, sending up suckers similar to those of the lilac. It produces lots of dark blue berries as well. If these are allowed to fall, the seeds inside them produce many seedlings. Again, a thicket results. I planted two mahonias years ago, and am reaping the consequences. But a couple of young suckers are ideally positioned someday to foil shortcut-seeking letter-carriers and the like, which may be one of those disguised blessings.
Another native shrub is the Snowberry, Symphoricarpos albus. Its white berries, borne on skinny stems, are striking in winter, but it spreads by running roots that send up shoots all around. One of my reference books says it’s “too rampant to be admitted to the garden.” Too late, in my case; I thought snowberry a fitting companion for my Garry Oak, since they occur together naturally. Now I spend quite a lot of time cutting unwanted snowberry shoots.
The Nootka rose (Rosa nutkana) is one of our two native wild roses, and yes, I have planted one here, close by the Oregon grape. It has that suckering habit, as I’ve found while edging the bed in which it lives. I’m thinking about removing the shrub altogether, but it takes me a long time to get to the point of actual planticide. The horror of finality, you know. In the meantime, the rose prospers and spreads.
Climbers and Groundcovers:
I have only one problematic climber, but it’s a doozy — Ivy (Hedera species). I have three kinds, including English Ivy (H. helix), which is branded an invasive alien here. It isn’t as sneaky as some of the other invasives, but bears careful watching and hard pruning. I recommend removing the flowering growths before berries ripen and are dispersed by birds. We have more than enough of this plant here. The other two types I have are not quite as aggressive, but I regularly whack them back before they cover too much territory, horizontally or vertically.
Winter jasmine (Jasminum nudifolium) hasn’t been a problem here — yet. It’s supported by a trellis, and I’ve been vigilant about removing any branches that touch the ground before they grow roots and develop new plants. Those unaware of this habit, take note.
Periwinkle is a great groundcover. Both the large (Vinca major) and small (V. minor) forms really cover the ground and anything that might be growing upon it. V. major is suitable only for large areas, but even V. minor can move pretty fast. Either restrict them to places where nothing else will grow (beneath evergreen trees and shrubs, for example) or be prepared to do a lot of control measures. I do both.
Japanese Anemone (Anemone x hybrida) is an attractive, late-summer-blooming plant, but it sends out running roots that pop up offsets from the parent plant, not always in situations where they are welcome. In my garden, these anemones are in a south-facing bed, and so want to spread southward, among shorter plants. This conflicts with my intentions for the bed, but the anemones don’t care about that.
There is a tawny-orange daylily (probably Hemerocallis fulva) that I brought to this garden when I came here in 1992. In books, it’s lauded as a plant for controlling erosion on banks. If I had known of its colonizing tendencies, I would have left it behind in Saskatchewan. Instead of forming clumps that become fatter and more impressive with the years, this species of daylily runs about, popping up where it pleases, even in the middle of other plants. Given enough space, I suppose it would eventually cover a large area. But that’s not what I had in mind, so have spent many hours digging it out. A double-flowered garden hybrid called “Kwanso” shares its parent’s running habit. When I was a newish gardener with space to fill, I gratefully accepted a gift of “Kwanso,” rather to my regret. With considerable vigilance, I have managed to confine it to a spot on one side of the pond, but regularly contemplate total eradication.
Phygelius aequalis or Cape Fuchsia is an impressive plant from South Africa, featuring clusters of long, slender, trumpet-shaped flowers in yellow or coral, on 3-foot, somewhat woody stems. It tolerates a certain amount of drought and even some shade. Maintenance consists of cutting the old stems down in early spring. Very nice, but it also spreads sneakily underground. You think it’s a well-behaved shrubby thing, until you find big, healthy sprouts yards away from the parent plant. Given that said parent is pretty hefty — 4 x 4 feet — one is enough. New plants showing up among peonies and irises are not welcome. (Too bad, says the Phygelius).
Irises, especially the bigger types, spread by growing new rhizomes, and can cover quite lot of ground if not attended to. I’ve read that one must divide and replant irises every few years to keep them healthy, but mine seem a bit too healthy, even the ones that rarely bloom because of excessive shade. Digging them up and replanting might be a good idea, if only to get rid of the unwanted surplus. To be fair, though, irises can’t really be called invasive. Iris cristata, a small, spring-blooming type, has slowly spread throughout a couple of my beds over the years, much to my delight.
Another unexpected spreader is a form of Gentian whose name I do not know. Its main bloom period is in March, but I’ve known it to produce a few flowers in fall and winter as well. Planted in a semi-sunny, tree-root-free bed, it has spread to cover an area the size of a (smallish) bath mat, coming into conflict with some bergenias on one side. I plan to take advantage of its vigor by moving a few divisions into another part of the bed, at present occupied by common violets, Viola odorata, another near-weed. Which reminds me of another violet with spreading tendencies — V. labradorica, a scentless but attractive type with purple-flushed leaves, that is a useful groundcover in dry shade. It’s fairly well-behaved, but should be weeded out from around small hostas and ferns before it gets too chummy with them.