They're new rhizomes, hard at work expanding the girth of your clump. They'll make it wider, either by rooting and sending up new culms, or by turning back up as new culms. Don't worry about winter in your zone bothering them.

If you want to divide the clump, do it next spring, when the plant first starts it's growth. I can't tell from the photo how big the clump is, but I wouldn't take it down to individual culms when dividing it.

I planted this in early April as a small 1 gallon container with 1-2 shoots showing. It now has approx 30 shoots and has filled the space I wanted it to. Maybe I picked the wrong plant for this spot. I wanted something tall & tropical but it sounds like I may be dividing it every year to keep it's size in check. I t has done remarkable, it is about 11' tall as you can see in the photo, the fence behind it is 6' tall. Thanks for the help.

Travis