Wait a minute. I'm painting it. Painted PVC has got to be more string trimmer resilient than painted wood. I'm assuming PVC sheet is jut as hard as PVC piping. I suppose I could go the extra mile and attach a pressure treated border at ground level.
Actually it's nowhere near as hard...and as 6768rogues says, aggressive string trimmer usage can actually chew up the trim...painted or not. If used in the way way you intend, you should plan on having some type of barrier. Never been a fan of having grass butting right up against any building material besides concrete. Doesn't take much to create a weed/grass barrier.
I'll throw in 2 more cents in regard to your project. PVC trim materials have there place, and can be a pretty much maintenance free material. Tradeoffs include preparation, careful installation, and extra price/costs. I've gotten lots on compliments on some of our work that has involved extensive use of PVC materials. But I won't pretend it didn't come at a much higher cost than other materials might have been. The use of it should be balanced with it's intended application and the cost involved. In certain instances there are likely other materials that can achieve acceptable results with less prep and at lower cost.
JMO.
