Can anyone advise me what this very invasive plant is. It is deep rooted and difficult to,get rid of. We have dug out as much as possible but it keeps rearing its ugly head!
mares tail, you'll never dig it out. Sorry.
The roots go unbelievably deep. The only thing to do is keep pulling it, preferably as soon as there's enough to get hold of. You'll weaken it but it's unlikely you'll eliminate it.
It's been around since before the dinosaurs and it's got form!
I beg to differ with some of the comments here. While I agree that it is very difficult to erdaicate this pernicious weed, it can be done. This is particularly true if the mares tail is still relatively small, as in your pictures.
I had a small isolated plot in my back garden that was overgrown and i discovered some mares tail in it. I dug down as deep as I could (to the base clay) at as distance of about a metre from the centre of each plant and removed everything.
Unfortunately, as mentioned, the roots can go very deep, as much as two metres according to the RHS website. But when the plants are young the roots are not going to be that deep. The main problem is is that, like some other pernicious weeds, it can regrow from the tiniest bit of root left in the ground..
So you have to keep a close eye out for new growth when you've removed them. To remove these new ones I also dug deeply around them but only a few inches from the centre this time and when I removed them I could see that I had all the roots.
I also treated some with a strong root-killing weedkiller. You have to bruise some of the leaves between thumb and finger before applying or spraying the weedkiller and repeat the application daily until you see them start to die.
It's taken me two years but they have now all gone. If you have a lot more than in the picture weedkiller rather than digging may be your best option.