If I'm to understand you right, you would only be keeping them in the garage during the overnight hours? Otherwise, their whole lives, from germination forward, would be spent outside in direct sun and exposed to the elements? If that's case, hardening off shouldn't be required. Plants sprout and grow in direct sun outside all the time, in fact, that's how they are designed. The only reason we need to harden off is because plants grown indoors grow for significant periods (often many weeks) without any exposure at all, and therefore, are much more weak, or tender then those that have had a much tougher life of germinating, sprouting, and growing in the outdoors. Edit to add: I have done this with cool weather plants like lettuce. Often times here on the Colorado Front Range "spring" means a day of 70F with an overnight low of 19F and snow, then 70F again the next day. By the time night temps are finally above the mid 30's, and heavy blankets of snow are not longer a weekly threat, the day time temps are already soaring towards and through the 80's. I sow the lettuce in trays and put them outside from morning to night time that way I can get them started without taking up room under the lights or having to worry about hardening them off. This post was edited by ZachS on Sat, Apr 5, 14 at 20:51

I would wait until after frosts have past before moving outdoors permanently. Once established, hardy herbs will do just fine but baby/indoor grown plants are different. And I agree with balloonflower - when you start getting mild days, begin hardening off your plants by moving them out during the day and back in for night. It is the best of all worlds that way. FataMorgana

If chilled will develop yellow growing points, indicating they may then be too slow to develop.

That is such a little beauty! Growing a flower scape so early must be so gratifying to see - and a reward for all that TLC, you seed-growers. There's nothing better, I'll bet. I feel the "proud papa love", Tim! Thanks for showing us your youngster. It's examples like these (and LUUK's photos) that makes me look at some of my burgeoning seed pods with new eyes....a new awareness. Jo