oh, you have my deepest sympathies!! if what you have is the white-flowered goosenecked loosestrife, as i do, it is a major thug which is determined to take over the world. i started with three plants 12 years ago and by now it has taken over an area approximately 6ft x 20ft.

a couple of years ago i tried to remove it by digging out the plants and sifting the soil, but the least bit of broken root left behind happily made new growth. i tried barricading it with 1ft. wide hard plastic -- it just sneered at me as it tunneled underneath and popped up on the other side. the roots are intertwined in a mass which makes it difficult to deal with, as well.

i cannot offer you any remedy as i have yet to find one that works. i have the suspicion that it would just tunnel under cardboard until it reached the edge and continue to romp in the garden. as for Roundup, i have not tried that as my gardens have a very high water table, complete with swampy woods on the backside, with lots of frogs and newts, etc. i dare not use Roundup in case it would destroy my critters.

what to do??! i hoe someone chimes in with a method to irradicate this loosestrife -- pretty tho it is, it is not a considerate neighbor to other plants! good luck to you, Grammie!

Since it is a tough plant you might need to try roundup. Try a small area and see if it works. I shoveled mine back but it always takes over. If it is mixed with desirables you could paint the leaves instead of spraying. Sometimes a little chemical will solve a problem or taking years of pulling etc. as much as I don't like using them I will in some cases

I love this plant!! I know it can be a problem but I find it behaves rather more nicely if you stress it a bit. More sun, less water and spreading growth slows dramatically. it doesn't try to take over the world.

No reason why it shouldn't respond to RoundUp or any other broadleaf herbicide if you are in a position to use such.

A non-chemical alternative to Roundup might be vinegar. I use regular white vinegar as a weed killer in my garden because I don't like using harsh chemicals. Vinegar kills whatever it touches so I'm careful to pour it slowly on the weeds--briars, crabgrass, dandelions, poison ivy--and avoid getting any on my plants. I pour it on both the foliage and close to the stems at ground level.