Asparagus Growing In Bags

Well, I bought a few asparagus plants last month in preparation for the new bed. My problem is John's book says plant out in May, but they have started shooting in the bags. Should I throw them in a pot and put them in the poly tunnel until April, or just get them in the ground ASAP, maybe with some fleece protection?

Thanks,

Kosh

prepare the growing area / bed add gravel in the base of the trench for drainage.
plant out in march once the major frosts have gone..