Isn't one of the major factors determining cold hardiness for a whole class of plants the amount of moisture in the soil during the coldest weather? I know of a number of different plants that are hardy to a much lower temperature where it is dry in the winter than where it is wet. Especially if they come from a region with typically very dry winters. For example, some of the mediterranean or desert palm species. On the other side, are there plants that are hardier to colder temperatures when the soil is moist than when it is dry during the winter? I've heard it said that there are a number of plants that the Denver Botanic Garden grows that are hardy there but not in the Eastern U.S. including some areas with somewhat warmer winters than Denver has. --Lee Poulsen Pasadena area, California, USDA Zone 10a On Nov 18, 2005, at 11:12 AM, James W. Waddick wrote: > Dear All; > This spring on a visit to the gorgeous Denver Botanic Garden, > I saw plants of Sisyrinchium macrocarpum growing like they were > perennials. Usually yellow flowered S. American Sisyrinchium are > totally tender for me in Zone 5. Panayoti K. confirmed they were > reliably hardy and pointed me to a Denver Nursery where I bought a > couple and then planted them outdoors. > Even after our recent 19 degree overnight low, they look OK. > > Anyone else have experience with Sisyrinchium macrocarpum in > a colder climate and any comments on hardiness in general?