We grow Bulbine frutescens as a groundcover here in Southern California. I have two varieties (at least that is how they are referred to here), one is 1-2' tall with yellow flowers and the second a dwarf (only about 10" tall) with tangerine orange flowers. Both colonize by underground stems. I have to whack them back every so often or those stems get really elongated and woody. If you want more detailed information, I suggest you visit the website of San Marcos Growers, http://www.smgrowers.com/ and search for bulbine. Just to give you an idea of how tough these plants are, the yellow ones I have came from a garden where a month before I visited, the gardener thinned hers out out and stashed the extras in a paper grocery bag. When I asked about the ones still in the ground, she offered me the bag full. It took me another month to plant them and they never missed a beat.... I also grow Bulbine latifolia (syn. natalensis) in a pot but that does not seem to spread and I don't know whether it has any underground storage structures.