Eating Weeds: Japanese Knotweed

When I first learned that Japanese knotweed was edible, I had my doubts. Sure, lots of plants may be edible, but are they really something you’d want to eat? I know Japanese knotweed as one of the most notorious weeds on the planet. Its destructive, relentless, and prolific nature has landed it on the world’s 100 worst invasive species list, right up there with black rats, Dutch elm disease, and killer algae. Having encountered a fair number of Japanese knotweed stands, the first thing to come to mind has never been, “that looks delicious.” Mature stalks stand as tall as 3 meters with broad, leathery leaves and hollow, bamboo-like stems. Their late summer flowers – a mess of tiny white florets on sprawling flower stalks – are a pollinator’s delight and favored by beekeepers for their abundant nectar. I don’t doubt that the honey produced from such an encounter is tasty, but the plant itself? I needed convincing.

Finally, I looked into it. I came across recipes of Japanese knotweed pickles and learned that it was the young, early emerging shoots that were sought after. That changed my perspective. Certainly you wouldn’t want to gnaw on a woody, 4 foot tall Japanese knotweed stalk, but the tender stems as they’re just beginning to re-emerge from the ground in the spring? Now those might be worth trying.

emerging stems of Japanese knotweed (Reynoutria japonica)

Japanese knotweed (Reynoutria japonica) was introduced to Europe from Japan in the 1800’s, arriving at Royal Botanic Gardens Kew by 1850. At that point, it was a prized ornamental. Its thick stems spotted with reds and purples, its broad, shiny leaves, and its showy flower heads all gave it garden appeal. It was also found to be useful for stabilizing hillsides and reducing erosion, honey production, and as a rhubarb substitute (it’s in the same plant family as rhubarb after all). Not long after that, it made its way to North America. Certainly people must have been aware of its propagative prowess as they moved the plant around. It readily roots from root and stem fragments, plus it produces extensive rhizomes, working their way as deep as 3 meters into the soil and as far as 7 meters away from the parent plant. Perhaps that should have been cause for alarm, but how could anyone have predicted just how aggressive and widespread it would soon become?

Thanks to the plant’s rhizomes, Japanese knotweed grows in thick, many-stemmed stands, pushing out, shading out, and leaving very little room for other plants. The rhizomes are also tough and can push up through gravel, cement, and asphalt. They are notorious for damaging foundations, pipes, and even pushing their way through floorboards. If that’s not enough, Japanese knotweed is pretty much impossible to kill. Herbicides may set it back, but they generally don’t take it out. Cutting it down repeatedly can slow it down, but it may also encourage it to grow more thickly and spread out more widely. Smothering it can work, but you have to be prepared to keep it smothered for quite a while. The deep rhizomes are slow to die, and they may eventually find their way outside of the smothered area, popping up to destroy your efforts to contain it. You can try to dig it out, but the amount of dirt you’d have to dig to get every last root and rhizome really isn’t feasible in most circumstances.

But hey, you can eat it, and perhaps you should. A quick internet search reveals a number of ways the plant can be consumed – purees, chutneys, compotes, sorbets. I chose to go with pickled Japanese knotweed. It seemed simple and approachable enough and a good way to determine if I was going to like it or not. Room temperature brine fermentation is pretty easy. You basically put whatever you’re wanting to pickle in a jar, add whatever spices and things you’d like, fill the jar with salty water, then seal it shut and let it sit there for a few days. Before you know it, you’ve got pickles.

There are several recipes for pickled Japanese knotweed to choose from. I went with this one. The seasonings I used were a bit different, and the stalks I had weren’t as “chubby” as recommended, but otherwise my approach was the same. After a few days, I gave them a try. I was pleasantly surprised. I thought they tasted a little like nopales. Sierra reluctantly tried them and was also surprised by how good they were. They reminded her of pickled asparagus. Other sources describe them as lemony, crunchy, tart and suggest serving them with fish, ramen, or even adding them to a cocktail made with purslane. Many of the weeds I’ve tried have been a fun experience, but not necessarily something I need to repeat. Japanese knotweed pickles, on the other hand, could become a spring tradition for me, and since we’re pretty much stuck with this plant, I’m sure to have a steady supply.

More Eating Weeds Posts on Awkward Botany:

Using Weeds: Soapwort

Over the past year or so I have written about several edible weeds in an effort to highlight useful weeds. However, weeds don’t have to be edible to be useful. In fact, many weeds are most certainly not edible, but that doesn’t mean they are of no use to humans. Soapwort, for example, is poisonous, and while it does have a history of being used internally as medicine, ingesting it is not advised and should only be done under the direction of a doctor. A much less risky activity would be to make soap out of it.

soapwort (Saponaria officinalis)

Saponaria officinalis, commonly known as bouncing bet, hedge pink, fuller’s herb, scourwort, and soapweed or soapwort, is an herbaceous perennial native to Europe. It has been planted widely in flower beds and herb gardens outside of its native range, desired both for its beauty and utility. Capitalizing on our appreciation for it, soapwort has expanded beyond our garden borders and into natural areas, as well as vacant lots, roadsides, and other neglected spaces. Even in a garden setting it can be a bit of a bully, especially if ignored for a season or two.

The stems of soapwort grow to about two feet tall, are unbranched, and sometimes tinged with pink, purple, or red. The leaves are oblong and oppositely-arranged, and their bases form prominent collars around the stems. Showy clusters of flowers are found atop the stems throughout the summer. Like other flowers in the pink family (Caryophyllaceae), they are cigar-shaped at the base and opened wide at the end, showing off 5 distinct petals with notches at their tips. The petals of soapwort flowers bend backwards, with their sex parts protruding outwards. In his description of the flowers, John Eastman remarks in The Book of Field and Roadside that “the reflexed petals surrounding the sexual organs give the impression of flagrant thrust; this is a gaudy, unshy flower.”

collared stem of soapwort (Saponaria officinalis)

The fragrant flowers are pink to white in color. They open in the evening and remain open for a few short days. In an individual flower, pollen matures and is mostly shed before the stigma is ready to accept it. This helps reduce the chance of self-pollination. Cross pollination occurs with the assistance of moths who visit the flowers at night, as well as bees and other flower-visiting insects that come along during the daytime. Soapwort fruits are oval capsules containing as many as 500 kidney-shaped seeds. Seeds aren’t essential to the plants spread though, as much of its colonization occurs via vigorous rhizomes.

In fact, vegetative reproduction is the means by which soapwort forms such expansive, thick patches. It also helps that it’s poisonous. The saponins – its soap making compounds – that it produces in its roots, shoots, and leaves deter most insects and other animals from eating it. It has a reputation for poisoning horses, cows, and other livestock, and so is unwelcome in pastures and rangelands. Saponins are also poisonous to fish, so growing soapwort near fish ponds is not advised.

soapwort (Saponaria officinalis)

Soapwort occurs in a variety of soils including sandy, dry, and rocky sites and is surprisingly drough-tolerant, fine qualities to have when colonizing neglected sites. While most other organisms ignore soapwort, it has a friend in humans. Eastman sums this up well: “Soapwort’s most important associate – as is true of most plants we label weeds – is undoubtedly humankind, without whose helpful interventions the plant would surely be much rarer than it is.”

I made a soapy liquid out of soapwort by following a recipe that can be found on various blogs and websites by searching “saponaria soap recipe.” Basically it’s a cup of fresh leaves and stems along with a cup of dried leaves and stems added to a quart of distilled water brought to a boil. After simmering for 15 minutes and then allowing it to cool, strain the mixture through cheese cloth, and it’s ready to go.

This gentle but effective soap can be used for cleaning countertops and other surfaces, as well as dishes, fabrics, and skin. Several sources say it is particularly useful for cleaning delicate fabrics. Sierra and I both found it to have a cooked cabbage or spinach scent to it. This can be masked by adding a few drops of essential oil. Despite its odd aroma, both Sierra and I were impressed by its cleansing power and plan to use it more often.

dried leaves of soapwort

soapwort soap

Summer of Weeds: Flower of an Hour

Hibiscus trionum is a great example of an ornamental plant becoming a widespread weed. Its common name, flower of an hour, refers to its short-lived blooms. Other common names include Venice mallow, bladder hibiscus, bladderweed, modesty, and shoofly. Native to southern Europe and tropical to subtropical parts of Asia and Africa, it was introduced to America as an attractive addition to annual flower beds. It is now naturalized in many states across the country.

Hibiscus is a huge genus in the family Malvaceae, consisting of species found throughout warmer parts of the world. H. trionum is a warm season annual that grows to around two feet tall and has the habit of a sprawling, decumbent vine; an upright, many-branched mound; or something in-between. Its leaves are alternately arranged and three-lobed with coarsely toothed margins. The flowers are solitary and borne in the axils of leaves. They are creamy white to pale yellow with a purple-brown center, and are both cross- and self-pollinated.

flower of an hour (Hibiscus trionum)

Flowering occurs on sunny days throughout the summer. The ephemeral flowers promptly produce a balloon-shaped seed capsule that is hairy and papery with prominent purple veins. Once mature, the capsules split open at the top to reveal five compartments lined with brown to black, kidney- or heart-shaped seeds. Every part of this plant is attractive and interesting to look at, which is why it is no surprise that it is welcome in many flower beds.

Seed capsule of flower of an hour (Hibiscus trionum)

Sites that are in full sun with fertile soil and regular moisture are sought after by flower of an hour. Less fertile soils are still prone to invasion. As with many weeds, disturbance is key, so it is often found in agricultural fields, rangelands, along roadsides, and in vacant lots and construction sites. Its presence in natural areas is a result of escaping from garden beds, agricultural fields, etc.

When we choose to grow plants that have a history of escaping into natural areas, we should be aware of both our proximity to natural areas and the dispersal mechanisms of the plants. Exotic plants that reproduce reliably and prolifically by seed, such as flower of an hour, should be considered unsuitable for gardens that are adjacent to natural areas.

This is because many popular ornamental plants have become invasive in the wild. Plants that are perfectly welcome in our gardens manage to find suitable habitat in natural areas, potentially threatening the livelihood of native plants and/or altering ecological processes such as fire regimes. An example of this where I live is bachelor’s buttons (Centaurea cyanus), which has escaped from gardens and invaded the Boise Foothills. While the impact of this invasion is not well-studied, the speed at which this plant has spread is disconcerting. Even more disconcerting is the fact that seeds of this and other European and Asian species are commonly found in “wildflower” seed mixes distributed throughout North America.

While I am sympathetic towards weeds, I also see them as one of the best reminders of the impacts that humans can have on the planet. They are clear indicators that every step we take has consequences. We should be mindful of this, and we should continue to have the tough conversations that issues like weeds and their impacts encourage us to have. There are no easy answers, but the dialogue must go on. Because all of us – gardeners and non-gardeners/ecologists and non-ecologists alike – generally have an opinion about weeds, they seem like a pretty good place to start.

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Quote of the Week:

From the book Invasive Plant Medicine by Timothy Lee Scott

The nature of a weed is opportunistic, and we, as humans, have created enormous holes of opportunity for these plants to fill. They have adapted to be at our side, waiting for those favorable times to cover the exposed soils that we continually create. With ever-changing genetics of form, function, and transmutation, weeds have evolved to withstand the punishments that humans unleash upon them.