Ask Mr. Smarty Plants

You are one dedicated gardener. Hats off. Just replacing one foot of dirt to get ride of nutgrass deserves some kind of medal. We're not quite sure what a bamboo type rhizome barrier is, but apparently you know and know how to do it. We'd say go for it. We're not sure which sedge you're referring to, there was no sedge in our Native Plant Database characterized as "purple". However, on further searching we found a "purple sedge" referred to as Carex purpurifera, still not in our Database. Then, we learned that a synonym for that is Carex laxiflora (broad looseflower sedge). We checked the USDA Plant Profile and it is native to North America and to Mississippi. That's probably not germane to your question, but we always like to know what we're talking about. Obviously, you already know you need to block further encroachment of the sedge into your vegetables, including grubbing out what has already popped up. The underground barrier, however, is not the total solution. This plant propagates by seed, which means you probably should either mow or trim the grass when it is about to set seeds and be constantly vigilant for fresh seedlings popping up in the vegetables. Here is a page of images of Carex laxiflora.