In the spring, Japanese butterbur has none of its
impressive summer appearance. But unimpressive or not,
it could still turn out to be a monster!
By Larry Hodgson
Question: Did I make a mistake in bringing home a clump of an unknown perennial from an abandoned garden last fall and planting it in mine? It seems to be spreading awfully quickly! Is it invasive?
I’m sending you photos, as I haven’t been able to identify it. It’s just not anywhere on the Internet. And it’s very odd, as it has two very different types of leaves. I have a sneaking suspicion that I might have planted a monster . . . and want to react in time if it’s going to be a problem.
Diane Beaudry
Answer: True enough, identifying this plant by its spring appearance isn’t easy. Most pictures in books and on the Internet show in its more impressive summer state. And it looks totally different in spring.
However, I recognized your mystery plant without difficulty, because I myself had quite a battle trying to eliminate it a few years ago.
The name of your plant is Japanese butterbur or giant butterbur (Petasites japonicus giganteus)! And your instincts are correct. It’s a very invasive plant. Enough so that it could swallow up your yard in 3 or 4 summers if the conditions were right . . . and if you let it!
I honestly suggest you do rip out this plant . . . and right away. The site where you planted it seems too narrow to hold it. And a spot so near a building will likely be too dry for this moisture lover, so it will never look good. But mostly, it’s simply an aggressive thug of a plant and potentially a seriously invader.
If you do decide to keep it, make sure it stays on your property. If it bulldozes its way into a neighbor’s yard, you might find yourself in court!
One Plant, Two Appearances
The Japanese butterbur produces its flower stalk early, before the leaves have appeared. They emerge first thing in spring on short stems 6 to 12 in (15 to 30 cm) tall surrounded by pale green bracts that pass for leaves. Each stem is topped with a dense cluster of small pale yellow compound flowers, like shrimpy dandelions. You’d swear it was a whole plant, not just a flower stalk!
In your photo, you can see it transitioning to its summer form. The flowers have turned brown, but the bracts are still green. They’ll soon dry up. Indeed, the entire flower stalk quickly dies back. A this point, true leaves start to poke out of the ground and will soon expand to full size. There are usually 3–6 per plant.
Japanese butterbur almost never produces seeds in a garden setting. That’s because it is dioecious: flowers of both sexes appear on separate plants. And, in gardens, plants of both sexes are almost never found together. Most I have seen are male. And with no female plant to accompany them, no seed is produced.
Description
The leaves are reniform (kidney-shaped). On sturdy petioles up to 6 feet (2 m) high (under the best conditions), leaves of P. japonicus giganteus are gigantic. They can measure up to 4 feet (1.2 m) in diameter. The name Petasites comes precisely from its large leaves. The name means “like a hat.” That’s because, when it rains, you can cut off a leaf and wear it as a rain hat.
Each plant also produces several underground rhizomes. They give birth to several offsets, then more rhizomes. So, in no time, you have a vast carpet of greenery. It’s a very invasive plant, especially in the wetlands it likes. But even in a well-drained flower border, butterbur spreads quite quickly: a rhizome can reach up to 10 feet (3 m) long in a single season. Because of the dense shade created by its huge leaves, it tends to smother nearby plants.
How to Grow a Japanese Butterbur
Maybe you’re in a situation where the invasive habits of Japanese butterbur are not a problem. If so, here are some tips on how to make it happy.
Japanese butterbur prefers damp or soggy soils, even flooded ones. And it’s under such conditions that it’s at its most invasive. It will still thrive in more normal garden conditions, where the soil is generally somewhat damp. But will invade a little less quickly there.
It’s less attractive in average garden soils, though. Unless its soil is constantly soggy, it tends to wilt daily in midsummer. And that’s not a very pretty sight. It prefers growing along the edge of a stream or a lake. It can even grow in a pond, with its roots slightly underwater.
This plant is pretty much indifferent to soil quality and even to light intensity. As a result, it will grow readily both in sand and clay and in sun or shade. However, for it to thrive in sun or sand will require a constant supply of water. Yes, soggy soil. As for shade, it prefers a location under deciduous trees. It will not do as well under conifers. Not only are they shady all year-round, but their shallow roots tend to keep the soil bone dry.
Slugs often damage the first leaves of the season, although later ones tend to come up intact. Photo: Rudolphus, Wikimedia Commons
The leaves are also prone to slug and snail damage, especially early in the season. And hail can reduce large leaves to Swiss cheese.
Finally, Japanese butterbur is very cold hardy: to hardiness zones 3 through 9.
Invasive, Yet Edible!
In addition to serving as an ornamental plant, Japanese butterbur is also a vegetable. In Japan, its young spring leaves and petioles are eaten under the name fuki. You have to learn how to prepare the leaves correctly; otherwise they are a bit toxic.
An Ornamental Variety
There is also a Japanese butterbur with foliage marbled creamy white in spring and pale green in summer: variegated butterbur (P. japonicus ‘Nishiki-buki’, syn. P. japonicus ‘Variegatus’). The leaves are smaller too: about half the size of those of P. japonicus giganteus.
I made the mistake of planting variegated Japanese butterbur in my perennial border. The nursery had told me that it was “less invasive than the species.” But after watching it rampage through my flowerbed for 2 years, taking over and pushing other plants out, I’d had more than enough of it. Besides, the real color was very short-lived. About 2 weeks, just after the leaves unfurl, then the leaf markings turned to a barely discernable light green.
There are many variegated plants that keep their color better than this one. And with much less of a hassle.
So, I decided to get rid of it.
I first tried to dig out the plants and pull out the rhizomes. But it just thumbed its nose at me and grew back. Finally, I got rid of it with the black tarp method: after 18 months under a light-excluding tarp, there wasn’t one living rhizome left. But I then had a huge section of garden to redo.
Lesson learned: “less invasive” means “plant at your own risk.”
Diane, whether you keep your new butterbur or eliminate it is up to you. But in the second case, I suggest you act without delay! Since you only planted it last fall, it won’t be well established. You ought to be able to dig it out without difficulty.