I usually wait for the 15th of March, but a quick glance at the 10-day forecast shows that it's not going to drop below 40 for the next 10 days, so I let my impatience get the best of me. Besides, this last weekend was perfect. It was cloudy, misty and warm and will be that way for a couple of days. I didn't even harden them off.
My main concern, other than a late March frost, is the heavier rain we are expecting today. So far, it's just been sprinkles and mist. Let's hope we don't have a downpour.
My other concern is that the ground will be too wet. I built up mounds about 6-12 inches from the soil line (clay-line), but after planting them deep, about half the root ball was below the regular soil line.
And yes, I know that the ground is not warm enough yet. But if I were to wait for that, it would be mid-April before I plant out. The plants will just have to deal with it.