horseradish

You might have to resort to weedkiller if it carries on being a nuisance! A systemic one would deal with it - but be careful not to splash any plants near it or you will lose them too.

The roots will go down to about two ft. before being safely cut or broken off.

They spread like wildfire Milky. I have one and am thinking of going in to horseradish sauce production big time. If you want to keep some for either sauce or the large green leaves then continue digging it out or as Spritzhenry says, if you want rid then glyphosate it. Probably several times.