Hi Pamela and Phil, Many thanks for the comments - very helpful. I have a large and growing collection of hardy cacti and am (as usual) trying to push the limits of a number of these. I have one bed that is about 35' long that I cover with 8' x 4' sheets of twin-wall, raised about 12" above the cacti, and this works well to keep the rain off, but doesn't help the temperatures. I was going to run some warming cables that I have through the bed, but I think I'll try the Dewitt's Ultimate row cover, based on your comments, under the twin-wall. The cacti I lose are because of a combination of cold and wet, usually in February. I have other sand beds that I can't cover to keep the rain off, but I could use the row cover. I think it would help a lot. I have always been very leery of using impermeable covers because of the risks of rot, but I've seen some discussion on cactus forums where plastic sheets have been used to good effect to keep cacti dry, and they don't seem to have suffered from the lack of ventilation and light. Best, John John T Lonsdale PhD 407 Edgewood Drive, Exton, Pennsylvania 19341, USA Home: 610 594 9232 Cell: 484 678 9856 Fax: 315 571 9232 Visit "Edgewood" - The Lonsdale Garden at http://www.edgewoodgardens.net/ USDA Zone 6b