I cannot speak directly to apricot, but I think the temps of the twigs is what matters most via air and sun. I frequently generate a tremendous amount of wood shaving in the shop over winter, Often I will dump them along and in the rows of blueberry plantings....on top of the frozen ground and snow. Those rows will hold the ground frost weeks beyond those that don't get this "treatment" and all still bloom together. (I don't do this in an attempt to delay bloom but just to get the stuff out of my way and on the berries) I also know folks around here who have tried to mound snow on their plums to delay bloom as well. That treatment seems a bit less effective in holding ground temp as long but they tell me it had no noticeable effect on bloom timing

Surprising to me there are no soil temps showing for my entire county of Mecklenburg yet Raleigh area has many reports. Wonder why that is? Don't know how to rely on such a map since there's no way of knowing if the readings are recorded in full sun or what time of day. Even the soil moisture readings have got to vary all over the place in one yard alone. But it was interesting.

a simpler way to put it.. is that you conifers DO NOT HAVE FEELINGS.. crimminey .. and frankly.. temp is irrelevant .. per se .. in and of itself .. its all about when tissue itself .. actually freezes .. and that would be not only temp .. but air movement .. ground heat .. humidity .. etc ... with hosta.. what i say is that in each individual cell.. when the water contained therein in freezes.. it ruptures the cell wall.. and that is when that cell fails.. in a hard frost.. the whole leaf will collapse .. in minor frost.. the leaf ends up speckled with brown dots a few days later ... either way.. there is cell failure due to the temps ... I DON NOT KNOW IF THERE IS EQUIVALENCY IN CONIFER TISSUE .. but i surely dont know why not ... all plants have cell tissue ... everyone got so excited about that warm VERY SHORT temp spike .. but in reality .. its been a pretty cold .. LONG .. spring ... and i am hating it ... in my z5 MI ... ken

Temp gain depends quite a bit on your climate. That is to say "sunny" varies a lot from place to place. Here in the CO mountains, with low humidity and low haze, the GH can gain 50 to 70+F degrees over outside temps. It often gets hot enough that some venting is necessary, even when only 20F outside. In other places I have lived, this was not the case, although there was definitely heat gain on their "sunny" days as well. So to answer your original question, I have to ask one in return, how sunny is your sunny? If you are in the SW, you'd probably be venting your GH in those conditions as it would likely get to 90F+. In cloudier and more humid areas of the country, you would get some heat gain, and likely not need your heater, but probably not as high temps as elsewhere (I'll let folks with more recent experience in those places comment).