Posted: 09/04/2017 at 14:45
It's ground elder. Treat them with a glyphosate based weedkiller but you MUST then wait until the tops have died down completely (about 6 weeks) or the weedkiller will not have translocated to the roots, which is the bit you really need to kill. Covering the ground won't help - I found a mat of roots under weed membrane which had been down 10 years!
The most effective time to spray is when they are growing strongly and just about to flower.
They will come back but weaker and if you keep it up you will eventually be rid of it, as long as it isn't coming in via a neighbouring property.