They'll be fine.

Rodney

The tops will naturally die back. Then come back in spring.

I'm in a slightly warmer zone than the OP but not once in a dozen years of growing garlic have I ever had the tops completely die back. Tip burn is the only damage I have seen. Maybe without mulch and/or a snow cover plus an extreme winter they could die all the way back to the ground but I don't think it's likely. And certainly not this winter which is forecast to be warmer due to El Nino.

Rodney

Here in Minnepolis, I always intend to mulch my garlic in the autumn, but whether I do or not top growth in the autumn is both common and seldom damaging. Currently I have some summer planted garlic that neither scaped nor dried off ( so I left most of it in place) and top growth in nearly all my autumn planted garlic of all varieties. Just about the only garlic that did not sprout were the bulbils. Japanese and Music lagged behind the rest, but a couple of varieties are nearly 10" high already. I refuse to worry about them. At least one of those varieties successfully maintained itself as a feral in NW Iowa (also zone 4) for nearly 30 years; so I expect to have some survivors at least in that one :). I planted in early and mid October this year much like in previous years, if maybe about a week early for some of it.

I worry far more about bed drainage, especially trying to avoid having melt water puddle in the beds during warm spells and spring melt.

Old Dutch, the variety we grow is also a unknown variety that was growing at a CSA in Northfield when the current owners bought the farm..we have had lots of opinions on what variety it could be, but all We or our customers care about is it is delicious, stores well..and Oh those tasty scapes :)

Rodney, thanks for the reply, it gives me some peace..We have only been raising garlic for 5 years, this planting is the sixth. Every year, we fight off the urge to KEEP more to use and sell...but slowly, year by year the crop is getting bigger

Last year we put in 425, this year 645..next year??

Thanks Everyone for your replies...Looks like the next week will be above the "norm" for temps this time of year.

Last year in June..our small crop :)