bee forage

Japanese knotweed: the surprising source of quality bamboo honey

Japanese knotweed is highly invasive but produces lots of honey.

Japanese knotweed is surprising, both for its invasiveness and for the lush crop of nectar it produces every year. Plus, the honey is superb.

Inside: Japanese knotweed blooms in the late summer when few other plants do, a boon for insects of all kinds, especially bees.

Japanese knotweed, Fallopia japonica (formerly Polygonum cuspidatum), is an herbaceous perennial in the buckwheat family, Polygonaceae. Many people think it is some kind of bamboo because of its hollow stems and raised stem nodes, but it has no relation to true bamboo, which is a grass.

Okay, we all know that Japanese knotweed is an invasive species, prone to tearing up your driveway, cracking your foundation, and choking rivers and streams. But what’s the best thing about knotweed? That’s easy: it’s in bloom. Right now. Japanese knotweed blooms in August and September when few other plants are even thinking about it.

The World Conservation Union lists Japanese knotweed among the top 100 worst invasive plants. But if you can look past that detail, it is a pretty plant with large spade-shaped leaves and showy cream-colored flowers. The plants may grow 5-8 feet tall in a dense, bush-like display.

At certain times of the year in western Washington, you can hear these bushes before you see them. They are alive with pollinators and are particularly attractive to honey bees. Many beekeepers manage to harvest a monofloral honey from the vast stands found locally. And if they don’t harvest, it makes a great late-summer boost to a colony’s winter pantry.

The honey is dark and flavorful, and many people compare it to a mild form of buckwheat honey. I’ve tried it and, personally, I don’t taste a resemblance. Still, it is good and worth a try—you can often find it sold as “bamboo honey,” especially on the East Coast. The sample I had crystallized quickly at a rate similar to buckwheat honey.

Bee lovers have found another use for Japanese knotweed. The hollow stems are often cut into lengths and bundled for use as native bee habitat. The stem diameters vary just enough to provide suitable housing for a wide range of tunnel-nesting bees, including mason bees and leafcutters.

The pictures below were taken in Kirkland, Washington yesterday afternoon. The owner of this invasive marvel says, “Standing next to the knotweed almost sounded like you were standing next to a hive.” She also said, “I hear knotweed is invasive and hard to get rid of. My sideyard looks like I’m growing knotweed as a crop. Neighbors have the same.”

Yup, sounds like knotweed. After it conquers the yard, it will conquer the house. Once the flowers die back, she should cut up the stems for native bees and get rid of the rest.

Honey Bee Suite

The honey bees are having a fine time in this residential crop of knotweed.
A honey bee and a fly share a late-afternoon sugar fix.

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  • Thanks for the advice. We will wait for the bees to finish having their fun, and then work on removing the knotweed. We’ll have to plant some enticing non-invasive flowers next year to make up for the lost habitat!

  • I’ve been noticing that most of the best fall honey plants we have around here are invasives:

    -Spotted knapweed
    -Sweet white clover
    -Queen Anne’s Lace
    -Purple Loostrife
    -Yellow hawkweed

    If it weren’t for them, the only significant honey plants we’d have this time of year would be goldenrod (which is unreliable) and a number of asters (which have kind of small, sparse blooms).

  • Well, we don’t have Japanese knotweed, and I hope we don’t get it. But common chicory (Cichorium intybus) is classified as a noxious weed here, and all I can say is Thank Heaven for chicory! My bees’ frames are full of bright white pollen, and nothing kills it or sets it back – a new crop of blooms every morning.

    The goldenrod is in bud,now, and if we get the expected rain from the remnants of Isaac, we should be OK for Fall. It is a MAJOR nectar source here.

    Oh, and I’m pretty sure chicory is introduced.

  • Where I live Himalayan balsam is the flavour of the month, you can see the bees returning covered in the white pollen as if they had been frolicking in flour. Also an invasive species!

  • Our golden rod is in full bloom and the knotweed should be blooming within the next week. Let the honey continue to flow.

  • It’s funny. I’m looking at that list from Tim above for all the invasive plants and we have everyone of them here in Newfoundland. Make no wonder our fall is usually the heaviest nectar flow. Although the sweet white clover and yellow hawkweed seem to be around for most of the summer.

  • Invasive yes. My town has already cut the knotweed down once and it’s all grown back in months time!! My bees are buzzing so loud, happy as can bee, or is me that’s happy? Either way goldenrod and knotweed are abundent and that’s a good thing!

  • I have knotweed nearby ..within a mile and a half. It is not near a stream. It grows in patches on hillsides. I’ve also seen it near homes that are miles away. I’ve read that the flowers are all female, making the seeds sterile. If so, how does it spread?
    I ask because it is a beautiful plant that was abuzz… When I put the car window down, honey bees flew into the car.

    • Kathy,

      The plant spreads by rhizomes which can be very, very long. If you cut up a rhizome with something like a rototiller, each of the pieces can grow into a new plant. Small pieces get carried around on tires, in streams, by animals, birds, etc. Wherever the pieces land, they can grow into a new plant.

  • I just harvested 77.5 pounds of Japanese knotweed honey between Covington & Black Diamond, WA… OMG it’s dark, darker than the buckwheat honey I’ve had, and the flavor is wonderful… You can’t even see the bottom of a tablespoon of this stuff. Mine tastes nothing like buckwheat, which I compare to molasses in taste. This has a very slight maple syrup flavor.

  • Japanese Knotweed root is one of the best remedies against Lyme disease. Read more in Stephen Buhner’s book ‘Healing Lyme.’ It is the plant that many vitamin makers use for their resveratrol supplements. Use those roots!

  • Hello from Romania! Thanks for the info.

    I’m a beekeeper and I’ve heard that bees can’t pass the winter only with this kind of honey, due to very quick crystalization.

    Here hundreds of colonies died because of it.

    • Ioan,

      I frequently overwinter my bees on crystallized honey. It’s not poison, it’s just a little short of water. Along with condensation from respiration, the bees do fine on it.