Too Early?

Over the weekend I purchased some plants for my tiny garden patch: some perennials and some annuals.  This time of year I'm anxious to dig in the dirt, but Laramie's altitude (over 7,000 ft) makes growing plants a challenge. As you can see on the graphic, the average date of the last hard frost is June 2nd, and by that time all the nursery plants have been picked over. If I don't purchase plants now, I'll be out of luck, but I don't dare plant them yet. 

I'll place them in the sun and water them during the day and move them into a sheltered area at night until at least the end of May when I will turn the soil in my tiny plot and put them into the ground. 

I'm trying to get a perennial bed started, but haven't had too much luck the last three years. This year, I'm adding two more blanket flower plants (one from two years ago survived another winter) and some salvia to attract bees. I couldn't resist the tiny geraniums (they were on a clearance rack for a $1 each), but I haven't had much luck with geraniums in this location or even in patio pots. I picked up some marigold for their cheerful yellow blooms. 

It's supposed to be in the 20s on Thursday and Friday night, so I hope my plan to keep these alive a couple of weeks works.