What a clever and easy idea. Mom's gone now and it would be a fun way to share her favorite Rose bushes with my Sibs. Grow Beautiful Rose Bushes from Trimmings with the Help of Potatoes (from Insanely Clever Gardening Tips Ideas")
How to make a Sub-Irrigated Planter. I'm not sure I would use a two liter plastic bottle though. Over time I would fear the plastic breaking down enough to poison the plant. Perhaps a wine bottle instead.