I have 8-10 of these big concrete planters, circular and about 3ft in diameter. I've pulled the old dead plants, mostly little evergreens or rogue ivy. Any idea what would do really well that is low maintenance, and can make it with fairly stagnant nutritional supply and shaky watering? I'm looking for something that will eventually fill out the whole planter so people throwing trash at the planters can't actually get their trash trapped inside. This association could go years before hiring anyone who fertilizes, but they want something beautiful and complimentary to what they have which has the potential to grow a few feet tall and be nicely shaped. The more minds, the more unique suggestions... Any ideas?