Only speaking from my experience. I have found that planting my garlic a month and a half from typical first freeze gives me larger bulbs the next year. I plant no later than the last week of Sept. here (zone 6A). It takes me 3 weeks to see emergence. My sprouts are 6" tall now and will probably give me one or two more inches of growth before winter. The growth will be "tipped back" and burnt on the tips before spring, but will remain green through a normal winter here. May not be the same in your zone 4.
Last year I was late in planting, two or three weeks, and my garlic turned out small and weak this year.
Mine is looking good so far this fall. Hope this helps you figure it out in your area.
hortster

Timing may be much more important the lower the zone where you're growing. That said. Here in Western Oregon, where it usually drops no lower than 15F, I haven't seen much difference between planting in mid Sept. or late Oct. and the little difference that I did notice was probably due to the weather.

First, I have only grown garlic for five years, so I am no pro. But I have been in horticulture for a long time and understand basic plant physiology.
I agree with madroneb's "Timing may be much more important the lower the zone where you're growing." But my theory (and that's all it is) is that the initial fall growth is responsible not for bulb development, but rather, fibrous feeder root development. It seems logical that the carbohydrates produced by the initial fall foliage go to them and ready the plant for better bulb growth in the spring. The better the initial root establishment the bigger the bulb. The reason that I theorize this is the years that I have planted "on time" and gotten a good sprouting have been followed by larger bulbs and much heavier feeder root systems when harvested. Late plantings with small sprouts have been the opposite.
Do some of you professional garlic growers have thoughts on this?
hortster

Hortster,
What you say sounds right to me. In areas where the weather drops low and stays there, the garlic goes into a close to dormant state. So the more root development you get in the fall, the readier the plant is to feed top growth in the spring.
In warmer zones like here in Oregon where it stays above freezing most of the winter, the plant development may slow, but never stops. And so if the garlic is planted late, it still has plenty of time to establish itself before warm spring weather kicks in.
Maybe Garliclady has something more to offer here. I may not be a profesional garlic grower but for 16 years now i've made my living growing organic vegetables and about 800 lbs. of garlic annually makes up some of that.

I planted a month ago. The left over cloves were peeled and put in a plastic bag in the refrigerator - they're all busy sprouting roots, not the green end. A few have nearly an inch of roots now.

I don't get it, why did you peel them and put them in the fridge?

I am just outside annapolis,maryland and i settled on november 15-20 for planting my cloves(largest from last year)....I will not cover them in straw until dec 7th and always dig down and have root growth...sometimes a inch or so of top-growth before mulching...After 20 years this is the time-line best for my area...I saw no benefit from extra(6-8 inches) of top growth when i would plant a few weeks earlier...many years i have no top-growth,but digging down confirms the roots have grown...

In upstate NY, I planted one batch in the beginning of october which now has sprouts 5-7 inches tall while the second batch was planted on the 3rd week of october at 1-2 inches tall now. All of them seem to be turning into rounds gradually and have lots of root growth already. Depending on the weather, the soil temperature should stay above freezing for at least another month so the root growth should be adequate for all of them to fully turn into rounds and be fairly established.

I could have planted them even earlier, but it seems like any time in october works fine. Also if they are planted earlier and have lots of top growth, simply adding more leaf mulch should help to protect them over the winter. I guess any time close to october for the northeast is good, and having them anywhere between 2-8 inches tall sounds like good growth to me. There's also almost always a residual layer of snow over the winter which means root growth probably can occur all throughout winter as they do seem to come back with much thicker shoots during the spring.

Here is a link that might be useful: Spring alliums of 2011

I don't get it, why did you peel them and put them in the fridge?

Dring the big harvest/food preservation exercise in the fall, when we'll be using dozens of heads of garlic in all the assorted canning, we've found it more efficient to take a few hours and sit outside under a tree and peel lots of garlic - so, say, when you need a 30 cloves for a batch of salsa, you just grab them.

These rooting ones were the large selected cloves left over from planting - and I guess, force of habit, we just went ahead and peeled them and popped them in the fridge.

Of the two varieties I grow, Tochliavri and Music, the Tochliavri roots in the fridge and music does not. And now, out in the garden, the Tochliavri is already 3-4 inches green above the ground.

That makes sense.
But if you want to try another alternative, next time you need to peel a lot of garlic:
Break the heads into cloves and put them all into a medium mixing bowl. Put another similar sized bowl on top (like a clamshell) and shake hard for 10 seconds.
I couldn't believe I went so long without knowing this easy way to peel a bunch of garlic.

Yes the double bowl method works beautifully! I can do 50+ cloves at a time and, depending on the type of garlic, it knocks off 70-90% of the skins, with the remainder loosened. I use large metal bowls and shake vigorously for about 20-30 seconds. The garlic I don't use in salsa gets chopped and frozen.

TomNJ

I've been using one of those plastic rolling tubes - I'll try the clam-shell method.

We use a food processor to mince and mix ginger and garlic, press it out flat in a plastic freezer bag, and freeze it - easy to break off chunks as you need. I should also try just freezing garlic that way - one of those 'well DUH!' moments......

I also press my chopped garlic into ziplock bags (about 6 bulbs per bag or 1/4" thick) and freeze. I call them garlic "books" and I put up about 20 of them each year. Very convenient!

TomNJ