I delight in the profusion of Spring pop-ups, including favorites such as hellebores and the weird, sci-fi flowers of butterburr (Petasites japonica), but one of the most exciting seasonal appearances is that of my little pop-up greenhouse. I set it up in early April and before long it's stuffed with seedlings. And I've got lots of other stuff waking up in there-dormant elephants ears (Colocasia spp.), many slumbering salvias (mostly S. guaranitica 'Black and Blue'), bromeliads, cannas (love that C. 'Tropicanna'), and more.
My greenhouse, a 6x6x6 cube that goes up as easily as tent, will go back to the basement by mid-May, when danger of a frost will be a thing of the past (Yahoo!). In the meantime, it helps me get a head start on containers and prevents my seedlings, like this Stipa tenuissima, from getting too leggy. Young tomato plants like it inside too. On cold nights, I toss a blanket over the top of the greenhouse for extra insulation, then crank up the little electric heater inside. Those plants are happy as clams. And so am I.