This contender for No. 1 on the Weed Horror Index is invading Southcentral Alaska

One gardener’s weed is another’s sacred herb.

Still, if you were making a horticultural weed horror index, my guess is dandelions would now be somewhere near the bottom of the index. They used to be way up there, but World War Dandelion has been lost and the weed isn’t such a horror anymore. Besides, they produce only 300 seeds per plant.

Chickweed, on another hand, can sport a staggering 2,500 seeds per flower. Still, chickweed would only be somewhere in the middle of my index. This week’s weed column covers Fallopia japonica, aka Japanese knotweed. This weed is at least near the top of the Weed Horror Index. It might even deserve the very top slot.

I realize most Alaskans wouldn’t know a Japanese knotweed if they were hit in the head with one. We need to change that right now. Let’s go interactive: Look up Japanese knotweed on the internet. Right now. Take your phone out and look it up. Go to images and get more pictures. Right now.

What you will find is an attractive shrub that can grow over 10 feet tall. It has segmented, hollow stalks, making it look like bamboo, only the stalks have purple speckles. The leaves can be nasturtium size and can even get to 7 or 8 inches, and are spade to heart-shaped with stems that turn red.

Japanese knotweed is covered with hundreds, if not thousands of small, white flowers that stand upright on their own stems. Unlike dandelions and chickweed, however, Japanese knotweed mostly spreads by root rhizomes, not seeds.

A rhizome is an underground stem that grows outward and has nodes along it that produce new shoots above ground. These, of course, produce more rhizomes ad infinitim. The plants are very hard to dig out.

Not only that, the brittle, bamboo-like stems can easily root too. They can grow in a wide range of soils with varying salinity and pH. One article discusses that they can sprout even after being soaked in salt water for two years!. This is a plant that wants to grow and spread. And it does.

You might think that if only a few Alaskans can even ID it, Japanese knotweed must not be such a big pest here. Well, sad to say, it is just now creeping up into Southcentral and the Interior, having escaped from Juneau and other parts south, where these plants have made inroads. They were probably imported as beautiful landscape plants. Oops.

The best picture I have come across so far shows Japanese knotweed stems growing through a driveway’s asphalt.

Japanese knotweed will easily grow through cement foundations too. Eradicating riparian banks is easy, and choking out streams is nothing. There are no obstacles. This is a plant that could take over the world.

OK, I think I have made my point. Here is the next point: This summer there have been four or five reports of this terrible, terrible weed being found in Anchorage yards.

If you see one of these plants, even if you just think you saw one (in your yard or in the forest while hiking, along the highway or wherever), please take a picture and send it to invasives.aswcd@gmail.com. Someone will get back to you very quickly. If you don’t, you and the rest of us will pay dearly.

Jeff’s Alaska Garden Calendar

Cow parsnip: There is so much more this year because all the seeds from last year produced more plants. That is how it works unless you remove seeds. They turn out to be a wonderful spice. Suit and glove up as the sap causes a rash that is exacerbated by sunlight. NEVER MOW THESE PLANTS as it releases the offending chemical into the air.

Alaska Botanical Garden: Could it get any better? So much in bloom. So much texture! Visit www.alaskabg.org and then go to The Alaska Botanical Garden. Join, too, and bring your Outside guests.