Ode to Oxalis: Not a weed...never seen a seed, nor will it impede any gardening deeds...indeed, so continue to read. This charming, easy-to-grow, clump-forming, winter deciduous oxalis has deep velvety purple leaves edged with a wide black border, topped by tiny, light pink flowers in summer...extremely cute! Purple shamrock is a dynamite plant to blend into the perennial border or woodland garden. Some of our Zone 6 customers claim to be growing this successfully through their winters.