Identifying knotweed
First off, there isn’t a single type of knotweed, there are many. Among the most common types are: Japanese knotwood (Fallopia japonica), Giant knotweed (Fallopia sachalinensis), Bohemian knotweed (Fallopia x bohemica), Dwarf Japanese knotweed (Fallopia japonica compacta), and Lesser knotweed (Persicaria campanulate). We are focused on Japanese knotweed because it is the most rampant variety of knotweed terrorizing property owners. So, when we use the term ‘knotweed,” we mean Japanese knotweed. We apologize to anyone who takes issue with our generalization. One of our goals is for readers to be able to plainly explain what they learn here to their next door neighbor.
Okay, enough of that. How do you identify knotweed? We’ve provided images and life stages in this article. However, when it comes to identification, there are a number of mobile apps that can ID it in seconds. They do a darn good job and it’s a lot better than walking around with a picture. Just snap a pic and upload it. Google image searches will do the trick and so will a mobile app for plant ID called “PictureThis.” They offer a free version that’s absolutely sufficient.
Identifying knotweed early can be a game-changer. It will save you time and effort. Even if knotweed has started to establish itself, the sooner you address it, the more likely you are to manage it. Time is your enemy. Find it and Act!
Knotweed leaf
Bright green, spade or heart shaped, small white flowers when blooming (typically late Summer). Baby knotweed leaves can be purple and red with red veins before mellowing to green (see “baby knotweed” image below).
Knotweed stem
Knotweed stems look like bamboo stems. They are hollow with nodes and internodes. They are mostly green with small purplish-red speckles. They have alternating (zig-zagged) leaves emerging from single nodes. The stem thickens and grows taller as it ages. Stems become tougher and woodier over time, then turn brown and become brittle as the plant dies back each season.
Baby Knotweed
(initial emergence)
Situation: Knotweed has arrived! Knotweed rhizomes have found their way to this spot and have sprouted for the first time. The bad news is that you have new knotweed. The good news is that it has not established itself and you can do something about it. Notice that baby leaves can be red and purple, with red veins. These colors mostly mellow into greens as the plants mature. Read about rhizomes and how knotweed spreads HERE.
Young Knotweed
(first year)
Situation: Knotweed is young and not firmly established. Presence is isolated; singular stems have diameters under 1/2 inch. Stem height is below 4 feet. If presence is limited, eradication efforts can still be on the lower end.
Established Knotweed
(2-3 years)
Situation: Knotweed has established itself. Stems are thicker, stem height is above 4 feet. Stems have clumped around larger rhizomes that have strengthened and spread. Hopefully, these more mature clumps are isolated and limited. Either way, it’s time to get serious.
Fully Established Knotweed
(5+ years)
Situation: The situation is serious. Knotweed has fully established. Rhizomes are large, deep, strong, and interconnected. Knotweed is taking over.
Planet Knotweed
Situation: Gulp…