I grow a number of Pacific Northwest native plants, including irises and lilies, and found that irises in particular do much better in styrofoam troughs than in black plastic pots or flats. Tried painting black deep band pots gray or white, and also tried styro boxes. The styro boxes outperform other containers for Pacific Coast Iris. I suspect their roots are cooler during warm seasons in the styrofoam. Painted some styrofoam boxes, found the paint is moderately durable, but birds do peck on it. Tried concrete patch, an epoxy product, and am now in the 4th year of testing this on styrofoam. I will say that if a cold frame collapses on the styro box that has been coated with concrete patch, it will crack, but then you can patch it up again. : ) I cut a number of drain holes in the bottom of each box, and use heavy plastic mesh, the kind used to hook rugs on, over the holes, and mix the potting medium with a lot of coarse perlite or gravel in it, so that it will hold up for several years. Kathleen PNW Coast, passing through zone 8 this year