Rampart grass

peteS

I've got a fairly rampant grass just starting to show it's self amongst my new phlox growth. I've no idea what it is, but it is deciduous, grows to about 12-15 inches, and has a very distinct green/white vertical variegation. I'm just wondering if it could do the phlox any harm by growing in amongst it.

Fairygirl

There's a grass called Phalaris  arundinacea picta [commonly called Gardener's Garters] which can be very invasive. It sounds like it could be that, although it gets bigger than 12/15 inches. 
Have you a photo?

peteS

Thanks for that. Looking at pictures on the internet it does look very much like that, although I've never seen it flower and the height stated is slightly more than what it has achieved. Although it is quite a striking plant, I do intend to dig it up, but do I need to remove the shoots which have grown amongst my phlox.

Fairygirl

It can be hard to get in about other plants to remove it [assuming it's that, of course] but it can take over  a border quite easily, so worth trying.
If you can't easily get to it among the phlox,  you may have to resort to just cutting it close to the base when you see it, which will reduce it's vigour.
If you can lift the phlox to get at it more easily and dig it all out, that would be the best solution if you can manage it.

Paul B3

Arrenatherum elatius subsp. bulbosum 'Variegatum' forms tiny 'bulblets' which can invade established plants . Strikingly variegated very narrow leaves .

I have a clump of this in my border ; flowers at around 10"- 15" high , then collapses during very late Summer .

I'm not saying that your grass is this species , but it sounds similar without a picture to ID with .

Paul B3

http://hoffmannursery.com/plants/details/arrhenatherum-elatius-subsp-bulbosum-variegatum