Hello Amanda!  Thank you for reaching out to UVM's Extension Master Gardener Helpline!

Japanese Knotweed is such a problematic invasive -- decreasing biodiversity in both plant and animal communities, degrading water quality and damaging human infrastructure (such as roads and bridge foundations), that I was surprised to learn that you are considering using knotweed stems to build pollinator houses with your 4h team.

After doing some research, I see that people ARE using knotwood stems to build mason bee houses -- although I haven't been able to find any information on this in our fact-based educational resources.  I did find several YouTube videos showing how to do this -- so I appreciate your thoughtfulness in writing to ask if this is wise.

I think the challenge is how to harvest or obtain the shafts.  When you cut back knotweed, the plant responds with survival vigor:  the rhizomes that spread underground fight back by sending up more shoots.  

Do you have a source that wouldn't encourage more growth unnecessarily?  I.e.:  perhaps as part of an effort to eradicate Japanese knotweed you have access to stems that reached maturity and then were cut down?

If you do, then perhaps you could leverage the project (while students are laboriously trying to cut the stalks into short lengths...) to offer some education about invasive plants.  

Here is a link to the Vermont Invasives site: 

   https://www.vtinvasives.org/https://www.vtinvasives.org/

If old enough, students could explore this site -- find the entry about Japanese Knotwood (in the "Land Gallery" under:  "Knotweed, Japanese."  You might ask what other invasive plants or insects they know about.

There are some great resources in the "Resource Hub" at this site.  Here's one that might help you explain what makes a plant invasive:

https://www.vtinvasives.org/sites/default/files/What%20Makes%20a%20Plant%20Invasive%20and%20FAQs.pdf

If you decide to use Japanese Knotwood stems for your pollinator house project, I hope you will find a way to obtain the dried stems without encouraging this invasive's spread and that you might take advantage of the opportunity to educate your 4H'ers about invasive plant damage and risks.

I was a Girl Scout troop leader for a decade -- so I appreciate what you are doing and understand, firsthand, what a difference you are making educating youth at this prime time in their lives -- THANK YOU!

- Robilee

Hi Amanda,

Robilee provided some wonderful advice for you and I wanted to send a quick follow-up to provide some more resources on solitary bee house making. Here is a nice overview of solitary bees and nest boxes written by our UVM entomologists: https://www.uvm.edu/sites/default/files/Extension-Community-Horticulture/BeepollinatorsupportbrochureDec2019.pdf

Nesting boxes (bee houses) are a great way to raise awareness about pollinators, the way they live, and how we can support them -- awesome idea as a 4-H project! One thing to keep in mind is to use renewable materials (like knotweed) for the tubes -- all tubes should be replaced annually (after bees emerge) to decrease risk of disease transmission from bee to bee.

For the tubes, you can use any plant with a pithy or hollow center -- it would be fun for the kids to explore different plants if you are in an area / garden that allows for that. And cheaper / locally sourced than purchasing bamboo or paper straws.

As for knotweed, as Robilee said, it is an aggressive invasive but it doesn't sound like you are planting or propagating it. Integrating knotweed into bee house making may make for an excellent teaching opportunity for the kids to learn about what invasives are and how to manage them as Robilee suggests. One of our volunteers provided some guidance on how she and others in her community are managing knotweed at:  https://www.uvm.edu/sites/default/files/Extension-Master-Gardener/How_to_Battle_Japanese_Knotweed_and_Win.pdf

In fact, this and other volunteers in Bennington County have hosted invasive cooking demonstrations (knotweed crisp and garlic mustard pesto, etc.) to raise awareness about invasives. And, did you know that J knotweed is an excellent pollinator plant (I have even seen some beekeepers make and promote J. Knotweed honey). I am not suggesting that we should be encouraging its growth but if you, like me, you live in a community along a river where knotweed is everywhere and is unfortunately here to stay, why not make responsible use of it and its hollow stems--the guidance in the resource above gives step by step instructions on how to "harvest" knotweed responsibly.

Amanda, we hosted a solitary bee house making workshop a few years ago for our volunteers and I still have a house structure and a few purchased tubes -- if you would like to them (the house as a prototype, etc.), I'm happy to hand them over to you. If interested, email me directly at <personal data hidden>.  

Yes, I have knotweed that I would love to eradicate.  Our forester has given us information as well.