When I pruned my grapes last year (for the first time, had been letting them grow larger however they wanted the first couple of years) I saved the most promising prunings and rooted them.

I now have plenty of rooted cuttings that have been rooted for at least a month now in 12 inch pots. After they rooted and leafed out some I've been putting them outside in the sun any time it was warm enough (daytime temps in the 50-60 range) and bringing them in whenever the nighttime temps went below 40.

They seem healthy and happy.

My question is when would be the best time to actually put them out in the ground with the established vine? Do I need to keep them sheltered until after the last frost, or would they be okay being put out and experiencing some freezing temperatures, given that they are rooted and the variety is not normally bothered by the cold?

Also understand just because they are leafing out, it doesn't mean they have a decent root system. The may have little or no roots or fragile roots. So, once they go outside, I would leave them in whatever containers they are in until they start putting out vigorous shoots, at which point they could be transplanted with less risk. In reality, grapes are tough and just want to grow, and will probably be OK, but I think better to let the root system develop.

I try to do all my rootings in clear containers, so I can tell when they've actually rooted (in soil, so that they're not just water roots) without disturbing them.