Thanks Uli. I encountered these tyemperature-controlled devices as a youngster about 70 years ago, but did not know that they were hydraulic. Are they still being made? Energy-saving, I'd think and need to be brought back or re-popularized for today's world . ----- Original Message ----- From: "Uli Urban" <johannes-ulrich-urban@T-Online.de> To: "Pacifib Bulb Society messages" <pbs@lists.ibiblio.org> Sent: Tuesday, January 20, 2009 5:38 PM Subject: [pbs] protected cold frame Dear Jane,Dear Jim, It was most interesting to read about your cold frames and thank you for the photos. I use a simpler different version to cover two beds on the base of my greenhouse wall: one for hardy cactus that need just protection from winter rain and one for tender perennials and half-hardy bulbs. It worked wonders last year but I do not yet know how the results will be this very cold winter. Some of the foliage at least looks VERY dead. I bought old commercial cold frame windows from a nursery, replaced the glass with polycarbonate (Plexiglas) which allows UV-spectrum rays through, is lightweight and will not break. These windows are leaning at an angle of about 45° to the wall and allow the wind to pass in order to avoid overheating on sunny days. For opening mechanisms there are automatic vent controls that work without electricity. I used several of them in my old greenhouse. Once adjusted they work forever very reliably, many different models are on the market, I think they were invented in England and use the expansion/shrinking of hydraulic oil in changing temperatures which is transmitted by cleverly designed levers to the windows that open and