As wayne indicates, these trees/shrubs are easily grown from cuttings. In the early spring, take some branches, add rooting hormone (or not, they root easily), plant them in good, moist soil. Put them in a shady spot for a few weeks and I bet you get some roots.

so my plan is to (after chemically treating them again next year)

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i dont understand this comment ... if you treated them at cutting down ... there shouldnt be a need to retreat ... though you might get a very few rogue sprouts ...

i guess i am concerned about how you plan on using the killer.. and why its a primary function of the rest of the project ...

and dont get me wrong... i have no objection to using such ...

also.. just for something to talk about.. why a container bed there??? ....

and if it were me... i would deal with that piece of fence ... if its yours ... it would be much easier to paint or remove it.. before you build something in front of it ...

welcome to the forums ... come back often ... winter is a great time to plan and talk about next spring/summers projects ...

ken

Ken, very few perennial weeds with a deep, wide spreading root system - like the Japanese knotweed - are effectively controlled with just a single herbicide application. It usually takes multiple applications over a period of years to eradicate fully....and perhaps not even then!!

As to the redtwig dogwood, these are suckering shrubs so very likely divisible when dug. Once fully dormant, I would cut back hard, dig and divide as bare root and then replant, either in the ground if feasible or in containers for future plantings in spring.

Three time per year for three years by trained contractors licensed to do jk removal using chemicals not available to the general public. That's what it took in my woodland. JK roots can be 12 feet down and it will regenerate from a fraction of an inch of stem or root. JK is treated as hazardous waste here.

What other people have said about the knotweed! My reasoning for tarping it over and making a container garden is that if it should resprout, I can still remove the tarp and containers and re-treat it. Unfortunately, it's coming into my yard from my neighbour's place (on the other side of the fence), and it's been difficult coordinating our efforts to kill it.

Thank you for everyone's advice! I love red twig dogwood and was planning on getting a few anyway, so I think I'm going to try propagating this one through cuttings, and if I can get the mother plant up, I'll check for divisions then pop them into containers for future plantings as suggested. I get the containers for free, and I hate to kill it if it could be saved!

You are better off washing off all the soil from the roots when you do dig it out. You don't want any knotweed coming along for a free ride.

Skip the rooting hormone. This is one of those plants where it is not needed. I had an indoor festive planter with red-twig in it one Xmas season. By the time January came the red-twig was rooted and started to grow. One of the easiest plants to root.

It looks like it has lots of suckers coming up from the base. Each one of those will have some root already attached. It's going take some work getting it out.