Lily of the Valley invasion

(Question)

Hello, Lily of the Valley are invading my garden. It comes from the back neighbors yard.
I tried digging a trench at the back at the fence and put a plastic barrier, nothing is working.
Is it permitted to use herbicide to kill the roots here, but it will also kill the same plant in the yard of our neighbor?
Would vinegar/salt/soap kill the roots or is this a surface treatment?
I’m usually manually remove plants but this will not work with this plant as it is propagating by rhizomes.
I spent 20 years getting our (50’x15′) sloping garden where it is from mud, dying bushes and rocks, I find it discouraging fighting a loosing battle.
Photos attached, the red circles is showing where the lily is invading.
I thank you for your advice.

 

(Answer)

Thank you for your query to Toronto Master Gardeners.  We cannot recommend any homemade remedies. However, here are a few suggestions:

  • Please see the answer to a previous question about a similar invasive plant, goutweed.

www.torontomastergardeners.ca/askagardener/this-invasive-weed-has-taken-over-the-front-garden

  • You might try defeating the culprit by planting strong shrubs and hardy perennials that can out-compete lily of the valley for space and nutrients. Best would be any with large leaves such as Ostrich Fern, Hydrangea, large Hosta. Be sure to pinch out any emerging sprouts in early spring as this will weaken the creeping rhizomes.
  • If you are patient, you could try to smother the lilies by using several layers of newspaper or large flattened pieces of cardboard boxes, tape removed.   Be sure no spaces show where the pieces meet. Cover these layers with about 6 inches of mulch, not compost, and wait a couple of years.

Good luck with your problem of the beautiful but bothersome invaders.