Knotweed in my raised vegetable beds

6 years ago

This is my first year gardening. The spring in Coastal BC was brutal this year with the entire month of April and half of May being extremely cold and wet.

We built the raised beds. I lined the beds with food grade plastic since we opted to build them from Douglas Fir rather than cedar. I lined the bottom of the bed with landscaping cloth which at the time I felt to be excessive given that the beds are nearly 2 ft tall. In late March we filled the beds with soil so it experienced about 6 heavy weeks of rain. I wasn't very happy with the soil blend I ordered....it seems to have a lot of un-rotted an fairly large wood chunks and is a bit sandy. I laid a layer of organic potting soil over the top of the beds to add some higher quality soil to the mix.
In the middle of May, I notice a strange red tipped weed poking up through the garden bed. I was sort of shocked that the plant was able to grow 2 ft through the soil. As the weeks go on, I find a red growing tips popping up in different areas of the garden bed. Only about a week ago did we finally bother to identify the weed and have discovered that it's the invasive "Japanese Knotweed." It's growing under our fence from a neighbor's yard under the ground and up 2 feet into my veggie garden!

I have been frustrated by my garden's performance this year and have been blaming the poor weather and the soil I bought. Finally I google "allelopathy knotweed" to see if this invasive plant is poisoning the soil similar to a walnut tree. I did find some results on studies done on native plants that do demonstrate it may have some allelopathic tendencies....but I'm wondering if the few shoots I keep finding can have that affect on my entire garden?
I started 9 tomato plants indoors and 2 weeks ago I planted 4 in the garden bed. They received adequate sun and water and seem healthy enough but aren't thriving. I planted two of the tomato seedlings in pots on my front balcony and 3 in a raised bed out by the front door-all in the same soil as the backyard bed. Those 5 plants are getting significantly less sun and for some reason are all looking a lot more robust than the ones in the veggie garden.

Does anyone have any experience dealing with knotweed in their vegetable garden? Is it possible that it's poisoning the soil?

Sort by:Oldest

Comments (5)

floral_uk z.8/9 SW UK
6 years ago
Allelopathy is not the main issue with Japanese knotweed. This is a plant which can grow 6 to 8 feet tall, root down twice that depth and spread to cover acres of allowed. It is the number 1 worst possible invasive species in th UK. I would stop even trying to grow vegetables until the JK has been totally eradicated. If necessary dig up the entire garden! I had it in my woods and it took 3 years to remove by a professional company applying industrial herbicides 3x per year.

Unfortunately if it's coming from the neighbour's you are pretty much scuppered unless they control theirs too. This stuff is so awful that it affects property prices over here and there are criminal charges brought against those transporting or dumping it.
User
6 years ago
I'm not sure if it will work or not, but I had an invasive called greenbrier, which forms extensive underground root systems. When the bit growing out of the ground was thick enough I would take a stem tube - the kind with a cap on them with a hole for the stem (purchased at a craft store that sells diy bridal stuff), and fill it with gly. I would then cut the end off the invasive and stick it in the tube and let it sit for a few weeks. The plant sucks it into the root system and starts to kill it. You have to be persistent but it definitely worked for me!
Related Discussions
Will this soil work for a raised bed vegetable garden?
Q
Comments (3)
have you got room for both whiterino? i would suggest use all the soil you create on site, add heaps of gypsum helps for most clays as does also adding heaps of or organic matter this could simply be covering it all with a good depth of mulch hay or the like. if you have room bring some of that other material in or simply buy mushroom compost from the farm and cover with that before mulching. i have created herb beds using on site clay. len Here is a link that might be useful: lens bale garden
...See More
termites in raised vegetable bed
Q
Comments (5)
Termites need a cool, moist environment to live in so their nests will always be in the soil someplace that is cool and moist. In the south, especially around the gulf coast there will be 5 species, at last count of termites, some of which will eat wet wood, although most species only dine on dry wood. Termites are a whiteish or creamy color, except for those flying out to establish new colonies and they do not have a waist. Ants have the pinched waist, not termites, so if what you have does not have a waist and is creamy colored you may have termites in that bed, but most likely they will do little to no harm unless you have some dry wood for them to digest.
...See More
New Raised Beds Vegetable Plants are Dying and/or Yellow Please Help!
Q
Comments (7)
The tree trimmings appeared to be very well composted. The consistency was very nice but the 90' temperature of the material would lead me to believe gardengal48 that you could be correct and it was a nitrogen shortage. Idaho_Gardener I would like to read more about the short and long chain acids so please post a link. Honestly you are speaking about my knowledge at this point. He did add some fertilizer and has seen an improvement. He kept a sample of unfertilized soil to get tested. Gumby all plants were purchased or started from seeds planted in the garden. It wasn't a transplant or hardening off issue. He is an experienced gardener and some of the plants from the same source grew in his traditional in-ground row garden just fine. Toxcrusadr- He recently added some fertilizer Wayne- These beds are 18" tall on flat ground. They drain well and drowning isn't an issue. The beds are in a spot had has gardened for years. They really aren't wood chips but instead compost made and sold by a company that operates a tree trimming service. They also sell topsoil and a garden mix. There were no discernible wood pieces or parts in this compost. It was very dark and crumbly like all other composts I've made or purchased. Magic Bean Compost Product Description I will find out exactly what he fertilized with and post and update. I haven't see the plants since he applied the fertilizer but he did tell me everything is doing much better. Thanks for the help
...See More
Question for planting vegetables in my raised bed.
Q
Comments (1)
5.5 feet is a bit wide for a bed in my opinion, because you will have to step on the soil to reach the middle. Those bushy zucchinis and crookneck squash might be good in the middle. Just one plant of each, in order to fit everything in, because those can sprawl a couple of feet in every direction. Cucumbers probably prefer to have a trellis, and the good thing is if the cukes are growing upwards, there's more space to plant your small things along side. Thyme and geranium I think are commonly grown as perennials, but I guess they can be grown as annuals. Yes, I think you can fit everything in there, especially if it's just one zuke, one crookneck, one, or two crowded cukes, a couple of kale, and then the other three along the edges.
...See More
Paul MI
6 years ago
"Gly" = glycophosphate (Roundup), I'm assuming? If yes, then I would add that the concentrate is even more effective. With hollow stemmed plants, after cutting the stem one can use a syringe to inject gly into the stem cavity. Cap the end with something like tape, wax, small piece of plastic wrap, et cetera.

I don't use gly often, but there are some plants for which I make exceptions.
mary_rockland
6 years ago
I got that cursed plant from a fellow gardener who called it "Mexican Bamboo". It seemed like a great way to make a quick privacy hedge. She said she just mows over where she doesn't want it. I only planted it in the lawn. I live in the country and have lots of space, but when it started coming up 30 feet away in a flower bed I'd had enough. I had only let it go a few years and then decided it was too greedy. It took about 5 years to get it "under control" and even 20 years later I still find it coming up in my lawn. We used round up for a few years and then after that every time we saw a darned red shoot coming up I cut it back and still do every year. Good luck.
Sandra Abrams
3 years ago
Did you ever get an answer to your question? I just bought a home with 3 raised beds I planned to use for veggies. I see japanese knotweed shoots popping up in the beds. The neighbor's yard is full of the shoots so they have spread to my yard and raised beds. I'm afraid to plant veggies in the beds if the knotweed is going to kill them.

Knotweed in my raised vegetable beds

Comments (5)

floral_uk z.8/9 SW UK

User

Related Discussions

Paul MI

mary_rockland

Sandra Abrams

COMPANY

BUSINESS SERVICES

GET HELP

CONNECT WITH US