Someone mentioned using spiderwort. I would add a severe warning to planting spiderwort anywhere! I planted a couple spiderwort plants to a fairly large garden and in 4 - 5 years the spiderwort completely took over the garden and choked out almost everything else in the garden. When we tried to dig it out, the roots were like iron ropes all tangled and knotted together. It took a great deal of work to dig up the entire garden to get all of the roots out. Even then I was still digging pieces of sprouting roots out every year for another 3 years to get rid of it completely. Cute flowers on the plant, but I believe spiderwort has plans to take over the world!