The Mackinac Grand has been a hard one for me as well, Anya--it's been stunted by late freezes every year since I got it. Are you sure you have enough of the feeder root left to support the eyes? If so, what have the temps been like? A lot of the time here they'll emerge then we'll have a cold snap and they'll just stay the same for a week or more, then start growing again when it warms a bit.
