I've got 2 pots of rhubarb seedlings that I started from seed. I know it's not the preferred way to grow rhubarb, but I enjoy growing everything from seed. I now have 4 seedlings per 2" pot, and I'm wondering if I need to thin them down to one plant per pot. When I look at rhubarb growing in the garden, it looks like a cluster of plants, but is it just one plant putting out many stalks?

Also, I have a 28" square planter box that I intend to plant the rhubarb in. Can I put more than one plant in this planter? There is nothing surrounding the planter, so the leaves can overhang as far as they'd like.