Tufa is much sought after by rock gardeners, but it is surprising how little information is available about what tufa is, how it forms, and what its properties are. In fact, I was able to find only one set of articles in the Quarterly (back when it was called the Bulletin) about tufa and that was in 1975 (vol.33: 158-161, 167-171). Yet many experienced rock gardeners are convinced that planting on tufa is the key to growing some of the more difficult rock garden plants in our problematic climate – Porophyllum saxifrages, tiny lime- loving rock ferns, and hardy gesneriads, for example. And tufa is intrinsically interesting and attractive, with its complex texture and intricate porous structure. But what exactly is tufa?