Happy first full day of spring, all! Unless you’re in the other hemisphere, of course, in which case, it’s the start of autumn. We could actually split the difference and say happy winter, since it’s still decidedly wintery here, no matter what the calendar says. I wish I could have done a Bloom Day post back on the 15th, but it would have been awfully short. So instead, I decided to write about one of my favorite perennials.
The burnets (Sanguisorba species) as a group are sadly underused, and I don’t know why. Granted, they’re not widely available, but they’ve been around for a long time, so it’s not like they couldn’t be more popular if there were a demand for them. Maybe it has to do with the reputation some have for being rampant spreaders, but many other aggressive perennials are easy enough to find. Burnets come in a variety of heights, so there’s at least one to fit any spot. And though they have a distinct preference for sunny sites, with soil that’s on the moist side, that hardly qualifies them as fussy or hard to please.
Like many other members of the rose family, burnets can be magnets for Japanese beetles. But in their favor, they don’t seem to be appealing to either rabbits or deer–at least those who live around here. Your mileage may vary on that front. [Edit: If you read the comments below, you’ll see that other gardeners do find that both bunnies and deer can be problematic. Sorry! I can only say that I haven’t…yet, anyway.]
I’ve been growing several species of burnets for years now, and each has its good points, but I’d pick Japanese burnet (Sanguisorba tenuifolia) as the clear winner for its vigor, stature, distinct clump-forming habit, and late summer-into-fall peak. Native to eastern Asia, it has a rather wide hardiness range over here: reportedly Zones 4 to 8. Best of all, it offers two distinct options in one species. The one with deep purplish red flowers usually goes by S. tenuifolia var. purpurea or ‘Purpurea’, while the one with white flowers is sold as S. tenuifolia var. alba or ‘Alba’.
Both lack petals–the color comes from the sepals–and both have a cylindrical inflorescence. The white is distinctly arching, while the purple is more variable: sometimes upright and sometimes arching.
On the purple, the stamens are very short, barely extending beyond the sepals (if at all), while on the white, they extend noticeably beyond the sepals, giving the heads a fluffy appearance. That seems to make the white much more attractive to bees and other pollinators, though I have seen them on the purple as well.
Habit-wise, the two are fairly similar, producing basal clumps of pinnately compound leaves with toothed leaflets (typically more shiny on the white than on the purple).
Slender, branching stems rise from the center of the clump, with the infloresences held at the very tips. I’ve seen a number of descriptions listing the height to about 4 feet, but here, established plants of both easily reach 6 to 8 feet here if left alone. They can also be sprawly, unfortunately, especially in windy sites, but it is possible to prevent or minimize that with pruning or careful placement of sturdy companions (more on that later).
As I mentioned, it can be difficult to find Japanese burnet for sale, especially in the U.S. Your best bet is to search for seeds (details on that toward the end). Expect seed-grown plants to take 3 or 4 years after you move them to your gardento really settle in and fill out. Once established, they seem fine without division. I have some clumps that are easily 10 years old and show no signs of weakening.
With all the variability in Japanese burnet–particularly the purple variety–there is a lot of potential for selecting distinct forms, so there will likely be more named cultivars in the future if the plant ever becomes more popular.
Pink-flowered plants sometimes pop up, too; ‘Pink Elephant’ is one that’s been named.
Have I piqued your interest about this underused perennial yet? Let’s take a look at its appearance through the seasons and see if I can convince you to consider it for your own garden.
Japanese burnet usually emerges in late March here in southeastern Pennsylvania. The basal foliage of established clumps can easily fill a space 24 to 30 inches across by early to midsummer, but its vase-like habit in spring provides planting opportunities for companion bulbs.
Small, early bloomers, such as Crocus tommasinianus and snowdrops (Galanthus), fit nicely right near the base. Taller, later bloomers, such as narcissus, tulips, and summer snowdrop (Leucojum aestivum), work well 8 to 10 inches out from the crown: far enough to come up through the burnet foliage but not get smothered before ripening.
Like other perennials with handsome basal leaves and tall, slender stems–giant coneflower (Rudbeckia maxima) is one that comes to mind–Japanese burnet poses a bit of a planting dilemma: Do you plant it near the front of the border so you can enjoy the foliage as well as the flowers, or do you put it near the back, where the tall flowers fit in better? Either approach can work.
If you’d like to keep your burnet up close, count on cutting-back if you want to keep it short or propping-up if you’d like to enjoy it closer to eye level. When I find seedlings at the front of a border or close to a path, I leave them alone for the first two or three years to let them settle in; after that, I cut the plants back hard in late spring to early summer.
If you’d rather not deal with an empty space for a few weeks, another option is to leave some of the outer foliage and cut just the center of the plant.
The lower you cut, the lower the ultimate height will be. Clumps pruned this way will end up taller than they would be if you had cut them to the ground, however.
That center-cutting approach also works well for Japanese burnet clumps in the middle of a border. In that case, though, cut the stems about 1 foot above the ground in late spring to early summer. The effect will vary somewhat but usually reduces the overall height by a foot or two.
If you’re going to grow either the purple or white Japanese burnet near the back of a border, consider putting it behind a bushy, medium-height companion that it can lean on, so it doesn’t sprawl.
Whatever you do, don’t depend on staking that will hold the stems too firmly. Part of the charm of Japanese burnet flowers is the way they bob and sway in the slightest breeze, adding movement to the garden.
Once you’ve made it past the late spring to early summer cut-back–if you decided to go that route–there’s nothing to do with Japanese burnet for a while. If you didn’t prune them, the plants may come into bloom in midsummer (by the end of July here); if you did prune earlier, expect them to start in late summer. Here, at least, the white form typically starts a full week or two before the purple begins to bloom. Once they start, the two usually overlap in peak bloom for several weeks.
Obviously, the flowers of the white burnet are brighter and tend to be more eye-catching. They’re beautiful against blue sky but show off even better against a contrasting background, such as a rich green hedge or vine or a dark wall or fence.
Contrast is even more important with the purple Japanese burnet, because the flowers are so dark that they can be hardly visible from more than a few feet away.
There is an abundance of excellent partners for both of the burnets during their bloom period, whether you prefer charming harmonies or striking contrasts of colors and/or flower forms.
If your burnet plants start to sprawl around this time, it’s very difficult to stake them in a way that keeps their natural loose form. I do sometimes use Y-stakes to prop up single stems or half-round plant supports to hold up a group, or else do a bit of judicious pruning to remove some weight from individual leaving stems.
If you find yourself having to do more than scattered propping, consider trying pre-emptive pruning or adding a bushy companion in front of the clump next spring.
White Japanese burnet usually passes its peak by early September here, but the purple goes on well into fall. Combination options continue with asters, grasses, and other late bloomers.
Purple Japanese burnet holds its color long enough to combine with the fall foliage of deciduous trees and shrubs, too.
Both varieties of Japanese burnet can be outstanding for fall color in their own right, usually turning bright yellow to golden yellow.
Japanese burnet (particularly the purple) offers some seedhead interest after flowering. The heads tend to crumble by mid-fall, but the remaining stems can linger through the rest of the fall, or even beyond.
As I mentioned earlier, seed is probably your best bet for getting Japanese burnet into your garden. If you find a source, I suggest buying only one packet to start with, to make sure that the source supplies the correct amount of properly cleaned seeds. It’s not unusual to get an envelope of chaff with few, if any, actual seeds, particularly through seed exchanges. The image below shows samples of uncleaned and cleaned seeds for both the white and purple.
I find that Japanese burnet self-sows freely here, but if I want to start plants for a particular purpose, I sow in fall or winter and leave the seed pots outdoors to germinate when they’re ready in spring. I’ve also seen advice that sowing outdoors in early to mid-spring, so the seeds can get around 8 weeks at 50ºF, will work. Or try the advice from Tom Clothier’s Seed Germination Database: “Sow at 20ºC (68ºF), if no germination in 3-4 wks, move to -4 to +4ºC (24-39ºF) for 2-4 wks.”
Because the first-year seedlings are small and wispy, I suggest planting them in a holding bed and letting them bulk up for a year of two before moving them to your garden.
Japanese burnet won’t be blooming for a while yet, so if you need flowers as soon as possible (and who doesn’t, after this endless winter?), consider adding some hellebores (Helleborus) to your garden. Whether you’re looking to learn more about these splendid shade-garden perennials or want to acquire some choice selections, there’s an exciting event coming up for folks in the mid-Atlantic region: the Hellebore Festival at Linden Hill Gardens, co-sponsored by Garden Design magazine. Linden Hill is located in Ottsville, Bucks County, Pennsylvania.
Jerry Fritz will be giving a demonstration on hellebore care on Saturday; hellebore expert David Culp will be speaking on Sunday. There will also be a variety of plant vendors, and a few non-plant (but gardening-related) vendors too, including me! I’ll be bringing many of my best botanical castings, as well as a series of new photo notecards, botanical sachets, and alpaca-filled nesting globes, among other things. For more information on this special event, visit the information page on the Linden Hill Gardens website: 2018 Hellebore Festival. It would be great to see you there!