I am wondering how practical it would be to raise Epis in a green house in the GPNW. I am not sure what minimum temperature I should shoot for. I have read if I am not mistaken that they can tolerate 45F, but I would guess that 50-55F is a better idea. How much external heat would I need during the winter? What should I consider in getting a greenhouse for such a use?
Epiphytic cacti are being overwintered here on Camano using an unheated lean-to that gets by on warmth from the house. Some more tropical plants have been lost recently but an Easter cactus coming through the same conditions flowered this month. A friend in Kent was leaving one of these hanging outside most of the year, putting it in his overwintering area only during frosty periods. Apart from efficient and affordable design the main requirement will be that it is large enough. Putting up a greenhose much bigger than you think you need has long been advised. In addition the particular plant you are interested in is rather large-growing. Multiple baskets of fully developed specimens could require a fairly large space.
depending on species, 55 would be the cut-off for lowest temp for most. 50's for some others. they CAN get quite large, so, initial size of the gh should take into consideration future growth and/or quantity of plants.
The amount of heat needed is solely a function of the cubic feet (or meters) to be heated, the temp you want to maintain, the temp outside, and the insulation (I think that it is actually the square of the differences between the two temps that you care about as opposed to the two temps themselves). I am turning a garage into a greenhouse using R30 insulation - as you can guess, the walls are not glass to any significant extent, so I need lots of artificial light - and a modest 500 Watt heater easily keeps 800 cu ft of space at 80 F even at 15 F outside. It was actually too hot for my 8 epis.
Yes: bright, humid and cool is what these want. I've never gotten them to amount to anything as house plants, whereas my assorted colors of crab cacti sometimes bloom twice per year with extremely little attention.
