I don't know about knotweed. For garlic mustard, most conservation authorities recommend waiting until plants are flowering (but before they go to seed) and cutting them as close to ground level as possible, removing the flowering stems from the site. They sometimes refer to studies which showed over 99% of the plants died when treated this way, presumably because most of the energy was spent forming flowers and they don't have enough energy to resprout. This method does not disturb the soil (where dormant GM seeds can stay viable for more than 5 years) but the timing is somewhat critical and cutting and removing the plants can be time-consuming.
Others have had great success using Roundup, but I've never tried it. Others report success in pulling all the plants before they flower -- although it is important to get most of the root system and you may bring up dormant seeds.
For a 250sqft area which had nothing but wall-to-wall GM, I smothered it with 10 or more layers of newspapers covered with mulch. Next year there were new seedlings on top of the newspapers (presumably because seeds had spread when I did this) so I repeated the whole process a second year. This year I had only a few seedlings/plants were there were rips in the newspaper -- so I am happy to say that I am on the tail end of the battle with GM in that particular area. However, that was in a garden area. In my woods the areas with GM are mixed with native plants, and in any case, the areas are too vast to use the newspaper method.
As to your method, if you can really remove all flowers so there won't be any new seeds -- yes, this will eliminate the GM (ideally in 2 years, except for dormant seed sprouting or carried in from elsewhere). However, since most plants will generate new flowering stems if you leave more than a couple inches of green, you have to go over the same area many times during a single season to get all the flowers.

I think it is always beneficial to do some cutting of any plant that you want to get rid of. As long as you are removing a significant amount of greenery you are hindering the growth of the plant- it will have to replace the lost growth and will use up stored energy and nutrients in the process. All plants can theoretically be killed by repeated cutting if the cutting is severe and frequent enough. However, the amount of cutting required to meet the "severe and frequent enough" criteria might be pretty extreme.

So, I think it is a good idea to cut knotweed as often as you can and as close to the ground as possible. Same goes for Garlic Mustard with the caveat that in pulling or cultivating Garlic Mustard you may disturb the soil and expose new seeds, which will then sprout and create even more GM. In my woods I go ahead and pull - I'd just as soon have the seeds sprout as have them wait a few years and then potentially sprout. Better to get the problem out in the open right now, in my opinion. In a more remote situation, where I might not visit again soon, then I might have to rethink the pulling and cultivating to kill GM seedlings.

Digging out knotweed works but, as you know, is a big job. We did an area that was a decades old infestation, probably about 50 feet by 50 feet, and it has mostly stayed out except on the edges, where for various reasons we couldn't dig down and get all the roots. Roundup will work pretty well too. On the big clumps, cutting the stem and putting full strength Roundup down it does pretty well, best just before Autumn when roots are taking up nutrients for the winter.

My experience with garlic mustard is that you can cut it, pull it, roundup it and everything works some. But the darn stuff just seems to keep coming back.

(Amazingly, I have seen colonies of garlic mustard living happily among japanese knotweed clumps. I thought nothing would grow there.)

thank you so very much for responding.

I will continue pulling at the garlic mustard.
I must make a note for early next spring to hit the rosettes with herbicide.

and, for a bit of diversity, I'll cut down what I can of the knotweed.

...the battle continues

Our park district does not cut Japanese Knotweed. They get to the knotweed during the height of summer. Inject 5cc straight, undiluted RoundUp into the plant stem above the first or second node. If you do it in the fall, it may speed up ripening of the seeds on the plant. Always dispose of invasive plant material in the garbage and not with yard debris.

Also, be sure to adhere to any state or local laws regarding the use of herbicides. Some of the stuff is really toxic and can get into groundwater systems.

I only pulled isolated garlic mustard plants. Disturbed soil is an invitation for germination of new plants. Weed whacking budding plants and RoundUp are better ways to go. Don't forget if you weed whack, that you have to take the plant down early enough so that the flowers cannot set seed on the cut stalks. GM is as good as dandelions at doing this.

GM seedlings are astonishingly resistant to RoundUp though sometimes when I have seen areas carpeted in seedlings, I've sprayed them anyhow.

Let me know when you want to have a go at the multiflora roses and shrub lonicera. :-(

My garlic mustard is very hardy. Smothering did not work, cutting (as per instructions from nature groups, etc.) encouraged new growth with multiple stems much of the time. The only thing that has worked at all for me is to pull it up. You will want to bag it, especially if it has seed pods already. What did work especially well for me, but was very labor intensive (and on hands and knees), was to pull up the rosettes during the warmer days of the winter.

I can see why most people on this formun have a hard time erraticating a biennal plant like garlic mustard,because most of the advice you're getting from them is downrigth wrong.Because of its two year cycle all you have to do is collect the seeded plants before they died and drop thier seeds,Practilly all summer you can go out and PULL UP the yellowing plan ts where they stand and collect them into big tight piles.The seeds are tightly bound to the plants until they completely die and turn brown.No weed wackers,no roundup just common-sense.This process repeated over a few years will elliminate the blight of garlic mustard with the least amount of work.If you have vast arces to clear have a gm party and enlist the help of friends,but get a keg.

I think one factor you have to consider with garlic mustard are the seeds that have already fallen and how long they may stay in the seedbank and keep popping up. For that reason, once you have removed something, it is a good idea to plant something aggressive but more desirable to smother it out. Pachysandra works pretty well. For a native, American Ginger will smother a lot of things if it finds conditions to its liking.

Unless you can mow it regularly, Japanese Knotweed is going to need root pulling. What to do with it depends on your municipality. I used to throw it in the garbage. Then one year our local landfill had an open house. I thought it would be informative to take their tour (okay the free hot dogs and hamburgers were a factor too). When they reached the yard waste area they had these gigantic piles of black mulch. The guide said everything was broken down - the only thing they had trouble with were bits of plastic (because when people rake tree lawns in our rather - to be blunt - garbage strewn town, there is usually an unhealty dose of litter mixed in that most wouldn't expend the effort to separate). I asked the guy specifically about Japanese Knotweed. As he explained it, their big pile process generated far more heat than the average home compost operation, and the mulch could be used without the fear of introducing weed seed or pieces of invasive roots.

Replaceing one nasty weed,garlic mustard,with another,pachysandra, doesnt sound like much of a solution to me.Have you ever tried to erradicate pachysandra?Its a pain in the a..Much harder than the garlic mustard.When removing a weed from an area,remove just the targeted weed nothing else.Leave the rest of the natives alone.the jewelweed,goldenrod,ferns,the wild blue lettuce,the blackberries and whatever else is there to hold the ground and prevent the re-emmergence of other nonnative weeds.You have to learn what belongs to your enviromental area and what doesnt.The biggest problem weeds that Ive enncountered in my gardening efforts are delibertly introduced ornamentals.Onced the area is cleared of weeds then you can be more selective.

Everyones experience is different, my experience with Japanese Pachysandra is on a long narrow patch of ground between a garage and a knotweed infestation. The initial plants I put in have spread at a moderate rate to fill this area - not one plant has come up outside of this range. It doesn't totally exclude knotweed sprouts but enables me to control them with minimal attention.

Hard to pull out? I have to watch out I don't accidentally pull out whole plants when I'm raking out leaves. I could probably pull every plant out of moist ground without any tool in a minimal amount of time if I wanted to. I find garlic mustard to be much more difficult to control than pachysandra, though I have managed to eradicate it from my property. The knotweed keeps coming from a neighboring property.

My experience is similar to bhrost. Having inherited a 40 year old patch of pachysandra in my woods, it fills a small gully where it is probably a bit moister, but I haven't noticed any spreading in the 3 years I have lived here. I like the fact that it is one of the few areas with no garlic mustard, which I figure will take me at least 4 years to get under control (I'll probably never get rid of GM completely since my woods are surrounded by neighbouring woods also filled with GM). Perhaps under better conditions (and not woods with a lot of maple roots) the pachysandra would be a problem.

I guess I'm just a purist,or maybe a bit compulsive,but finding a patch a pachysandra in the woods behind my house would be,for me,like finding a rotting old carpet that someone dumped 40 years ago lying out on the ground.I'd be compelled to clean it up as soon as possible because,unlike the carpet,it will keep getting bigger and bigger.pachysandra=growing trash

Nywoodsman, it is largely a matter of priorities and amount of available time. For people battling invasives like GM and buckthorn, which seed prolifically and likely are present in areas surrounding their own property, a bit of respite while they battle these is welcome. I'd probably temporarily even welcome an old carpet in my woods if, like my patch of pachysandra, it meant there were no GM or buckthorn in that area. My priorities are largely set by the conservation authority's list of invasives (and their relative degrees of seriousness) in my own area -- GM and buckthorn are very serious threats to the woods in my area, pachysandra is not.

Since the title of this forum is "woodlands", I think the orientation of most participants here is to garden in such a way that their patch of woods stays in as natural or native a state as possible, to the exclusion of non-native plants. I certainly respect this viewpoint and follow it myself in my own garden to the degree possible.

In principle, I would agree with the philosophy behind NYWoodsman's statement that:

"When removing a weed from an area,remove just the targeted weed nothing else. Leave the rest of the natives alone.the jewelweed,goldenrod,ferns,the wild blue lettuce,the blackberries and whatever else is there to hold the ground and prevent the re-emergence of other nonnative weeds.You have to learn what belongs to your enviromental area and what doesnt."

In actual practice though, unless you're talking about only a few weeds that need to be removed, this philosphy often doesn't work very well - for instance, it doesn't work very well when the area in question is all knotweed and garlic mustard, to the exclusion of everything else, like the miles and miles of riverbank in my part of NY state.

It seems apparent to me that in those instances the surrounding remnants of native vegetation that "belong to this environmental area" have obviously been spectacularly unsuccessful at stopping the knotweed and mustard infestations in the first place, so that re-planting these indigenous natives in a spot newly cleared of the latter two weeds .... or expecting them to fill in from the margins .... is an quixotic exercise in futility and doomed to failure. The knotweed and mustard will simply choke them out again in short order as they did in the past. How are the indigenous plants supposed to "prevent the re-emergence of non-native weeds" when they weren't able to prevent their initial emergence to begin with?

In those instances I think it's legitimate to be a little less purist. One's first approach could be to utilize a native plant not indigenous to the newly cleared site. I suggested American ginger, Asarum canadensis, as a good choice, which I have put to extensive work to good effect on my own property. Where happy, it spreads rapidly, forms dense patches, smothers noxious plants and virtually all non-native, non-woody plants, but still allows most desirable eastern natives to pop up through it.

One's next resort might be to try a desirable non-native which might be able to succeed where the natives failed. If you flat out just detest Pachysandra then of course you wouldn't want to use it in your woodland, but personally I'd rather see a forest floor covered in Pachysandra than one covered in knotweed or garlic mustard. Pachysandra is not invasive in my area or difficult to remove. It's often a good choice for tough problem areas, such as ground newly cleared of more noxious weeds, but is also often a good choice for more desirable locations. I've seen it used extensively at places such as Longwood Gardens, and many garden writers, such as Michael Dirr, sing it's praises. While I don't consider the opinions of Dirr or any other so-called garden expert to be the last or most authoritative word on anything, I do take note when their observations match my own.

Purity is probably a goal which we should strive for in our woodlands, but Pandora's box was opened quite some time ago and a lot of non-natives like knotweed spilled out which apparently are far more successful in some of our woodlands than the pure native plants. Re-introducing the evicted natives directly back on to the same ground can only work ... and probably not very well ... with constant weeding. If you don't have time for that, then you have to be pragmatic and try something else and employ some artifice - which is what gardening is all about. In a way, like politics, gardening is the art of the possible. Oftentimes the ideal, like the purity of pre-Columbian woodlands, isn't immediately possible or practical or within reach, so we compromise to attain a better situation that regretably falls somewhere short of the ideal, but is still better than the alternative.

I'll have to try the ginger (which we call Canadian ginger up here :)) I've been using woodland and creeping phlox for this purpose, because they spread so well in my cultivated shade gardens, but it remains to be seen if they will spread in my woods and keep GM at bay.

Hi Folks, I just wanted to throw in my $.02 on the subject of controlling Japanese Knotweed. This past week I spent two days removing the knotweed from hill along the side of my driveway. The infestation had been growing for about two years and spreading rapidly.

In my case, the hillside that was covered in knotweed also had some plants that I wanted to save- some sugar maples, four varieties of ferns, and some viburnum, so using a foliar spray was out of the question. Instead, I used the "cut stem application" as outlined in this document: http://www.pullman-wa.gov/content/WYSIWYG/Recreation/Japanese%20knotweed.pdf

The document recommends cutting the canes between the first and second node and filling the "well" with concentrated herbicide (I chose plain Glyophosphate, you choose your own poison). The document claims this method is 95% effective. Another method involves injecting the plant with herbicide using an injection tool. The upside to this method is that you don't need to dispose of the cut canes.

In all, it took me just about two days to clear the hillside. I cut enough canes to completely fill my 8' truck bed two times. I'll keep an eye on the area for the next year or so in case any survivors pop up.

-Josh-

Some weeds can be a blessing. I used to try to destroy my knotweed. When I bought my house, the realtor sympathised with me about the stand of it in the back and even suggested an illegal way of destroying it.
Just a few years ago I began to notice how beautiful it is, and how it makes my yard more private in the summer. Its blossoms are big, lovely and fragrant. It is an essential addition to my compost pile. I do not allow the roots to go into the compost.
Depending on where it grows and what your soil and climate are like, it may be a plant you can live with. Apparently my clay soil keeps it somewhat in check. It doesn't seem to be going to seed. I keep the back stand isolated by mowing. I pull it out of the other areas as it shows up, and add it to the compost green. In the spring I add the dried canes to the compost. I have even started fertilizing it. Getting rid of it is a lost cause-it is all over the neighbor's yards, and I could not keep it out of my yard wiithout a ridiculous effort.
The shoots are edible when very young, taste like asparagus.
This isn't to say that it can't be a pest even in my yard. It is a very stuborn invasive. But I love it anyway.

Paulaj. I agree with your view that every plant has merit. Even the Japanese knotweed has points that make it attractive - I've heard other people comment that it looks attractive (usually when it's flowering). I saw one interesting use of it in a big pot, where someone got it to send up lots of shoots so it looked like a bamboo thicket in miniature. If it was hard to grow and non-invasive, it would probably have a following. I dislike it mainly for the miles of riverbank it covers where it smothers out many of the natives, and makes walking almost impossible now without a machete. On many properties it is coming up because those properties are grossly neglected. All the same, it may serve a screening function for people who might have to look at something worse.

Garlic Mustard cannot out-compete plain old blue fescue grass. Seed your garlic mustard patch with blue fescue in early spring. The garlic mustard cannot grow through it. Pull up or burn off the fescue. Fescue especially hates being burned, and dies. It's also easy to pull up. Do this for 2 years running and you suddenly have a handle on the GM.

It's what we use to control GM in the State Parks around here.

There is a native pachysandra, too. It would be better to plant that one, as opposed to the japanese one.

paulaj and bhrost, I agree with you that there are redeeming qualities in Knotweed. I loved seeing it in August when the blossoms come out. It was simply amazing to see the variety and number of bees that would flock to the plant.

I did got to war with it since I could see that it was spreading and everything I'd read about it convinced me that the spread could not be checked. I even tried to save a small patch for the bees, but I did not realize how vigorous the plant was. It had to go.

The battle is not over but I've gained the upper hand for now. I'll need to remain vigilant as there are small patches sprouting here and there.

As for the bees, they seem to love the Joe Pye Weed I planted in part of the former Knotweed range.

All plants in isolation posess beauty.Even the lowliest weed displays the sublime sysmetry of a biological entitie.Some of the worst invasive plants are the prettiest.Purple loostrife comes to mind.One of the reason the plant was so widely planted was because it is attractive.An invasive weed's uglyness is in its infective nature,like an unchecked desease organism multiplying without bounds destorying the ecological balance of the ecosystem its invading.The resulting destruction is similar in appearance to an bodily organ invaded by tumors.The plage of invasive weeds is frighteningly apparent to those that understand though maybe subtle to those that don't.But be assured its destrutive potential is real and the resultant loss of biodiversity and beauty tragic.
Still like that knotweed hedge?

It will take time and persistance, but GET RID OF THE GARLIC MUSTARD (I have no experience with Knotweed, so I'll leave that to the others). This is an invasive species that damages our wetlands, forests, etc., blah blah blah -- you've heard it before here, and I agree 100%. Our local conservation area authority allows it to grow but not flower, and then severs it at the ground level. You will have to do this numerous times throughout a number of seasons. There is no quick, one-step, winner-takes-all approach. Roundup, or any pesticide, can be avoided here. All you have to do is put in a few hours every couple of weeks to get a grip on it. The GOOD thing is that IT CAN BE DONE! I have cleared a 65-foot by 20-foot patch in my back yard (that opens onto conservation land) almost completely (I'm at 98% GM-free!!!). I have been at it for 5 years now, but the BEST thing is that after the first two, your work will be minimal. View it as a garden chore - not so much fun but essential.

In my experience, garlic mustard is one of the easiest invasives to eliminate from a given area, knotweed one of the hardest.

Garlic mustard is a shallow-rooted biennial. Pull the plants out when in flower or just before flowering two years in a row, and no more garlic mustard. Do it when the soil is moist and the plants come out very easily. This is a great task for a scout troop on a sunny late-spring day. You can clear a fairly large area very quickly.

Knotweed is a perennial that spreads by rhizomes as well as by seeds. If you cut the roots while trying to dig it out, each piece of cut root that remains in the soil will produce a new plant. It's a dreadful curse that's best handled when it first appears. Once it takes over, I really don't know if it's possible to eliminate it.

Dilute at the rate of 1 part herbicide to 40 parts of water for treatment of most prenial weeds and 1 to 40 for treatment of hardy invasive plants like Japanese Knotweed and 1:20 for Ivy

Here is a link that might be useful: Knotweed Control