Is there any way that you could easily shade the green house during the day time? Even a white sheet over the top of it would allow sunlight to penetrate but would still reflect some of the light producing light waves. Does your greenhouse have some sort of ventilation so that some heat can escape during the day? I don't see much problem with the high temperatures you've mentioned, but as the days continue to get longer, and the outside temps more temperate, you may have some daytime temps that are simply too high. If not to both of those questions, I wouldn't worry about it too much. Large temperature differences can actually accelerate the ripening of some greenhouse crops! Especially citrus. By the way, all of the plant species you've mentioned do quite well in very chilly temperatures, as I am sure you've already discovered.

Was more or less wondering if I can get away with planting it in the open. I have more space to plant it there. The walls are starting to fill in.

I know exactly how you feel; I've been there before. But you already know (in the back of your mind) it doesn't really matter what we've experienced ;-) Different container sizes, materials, times of year, and the rest of micro-climate influence is too great to be helpful enough to answer your question. Oh yeah, rootstock is kind of important too! Mike you are correct and worrying about the right things. WLD may not be an issue for just one day, but root-loss is. The soil temp gauge is your best friend in these times. If you determine the container soil temp differential between ambient air temps, it should give you a good idea. If you want to be on the absolute safest side, don't let em get below 55. But IME they can get down as low as 40 and not die... heck I let one get to 35 (which I'll never do again) and it didn't *completely* die. To answer your question, I've lost orange and mandarin trees on C-32/C-35 rootstock with unprotected plastic 16"-20" containers in the gritty mix when ambient temps went to 28F. Other *unprotected* citrus trees did fine that year were: * on Trifoliate rootstock, best overall compared to Citrange and hybrids. * in over-sized containers, ie. the roots were not grown to the outer container edges. * in bagged soil, whereas gritty mix suffered more. I covered the foliage that year, not the containers. Although all the above trees "did fine" they did not thrive with the first growth flush, which should've been the biggest. It took half the growing season for them to act like healthy citrus again. Those which I protected the containers all did excellent and never seemed to languish. Looking at your trees and the excellent care you provide them, you want to stay around that 50+ range =) It's just not worth the disappointing and frustrating remainder of the year caring for plants that look so much worse than they could. I've done it! Why not buy some bubble wrap and put it around your trees containers. A lot easier than lugging plants inside. Just watch high-end peak temps ;-) It wraps back up nicely and re-usable. Hope your trees do great!

Actually, it gets pretty cold here where I'm at. We have already had close to 10 days this year below freezing and many of them in the 20's and one day at 19*. Last winter, before I planted any of my palms, we hit around 20* as well and had many, many freezes. First was in October when we hit 32*! We had a total of about 1 week of temps in the 20's... not all together, but 3 in a row one week. We often get below freezing until we are into March and I've even seen it even happen then a few times. The last 3 winters have been getting colder and colder for us... seems more like the 1970's and 1980's when we had a lot of cold weather down here. After some snow flurries and some sleet yesterday and a high of 35* we need to warm up! BTW, it was 23* this morning and they are calling for colder weather tomorrow morning.