I live in Zone 4 (Minneapolis area) and I'm wondering if it's possible to plant garlic too early for overwintering? I had a bed free up earlier then expected that I'd like to turn and mulch but I don't know if it's possible to overwinter too early and what effect it would have on the garlic?
The normal seasonal existence of garlic in the wild is to remain in the ground all year round. We interfere with this routine by digging, splitting and replanting to achieve a number of goals. We can improve the soil where the next crop will be planted, we can divide the cloves as required to increase harvest, check for clove health and we reduce the possibility of disease and damage while the bulbs are dormant over the summer by keeping them totally dry out of the soil.
Early planting would interfere with only one of those goals - by planting early the cloves go back into the soil where pathogens live and the risk of damage increases. Re-growth will only be triggered when the plant is ready to do so, so early planting brings a slightly increased risk of loss of planted materials, but in many cases the risk is quite small.
I disagree a little with Colin. In southern Wisconsin (zone 5, usually), I plant garlic in mid- to late October. One year I planted it early in October and the weather turned warm, causing the cloves to sprout later in the month. The leaves reached over 5 inches by mid-November, even though I kept covering them. The winter was about typicalfor our "new" climate, but when spring came the leaves had frozen to ground level; the onset of new growth was delayed, and the cloves produced were not as large as normal (variety was German Porcelain).
So, yes, I think you can plant garlic too early.
As Colin says in the wild the cloves are already in the ground so clearly it can survive just fine if just left there.
The timing of your fall planting is critical. Your objective is to time the fall garlic plantings so that the cloves have a few weeks to establish good root development before freezing weather conditions set in. Yet you don’t want to plant the garlic seed so early that the seed cloves have time to send up above ground leaf shoots before cold temperatures halt the plant’s growth.
If you get a little leaf growth before winter strikes don’t worry, your garlic plants will be just fine. The formation of an established root system during the fall will prepare the garlic plants for an early emergence and promote rapid growth at the first signs of the arrival of spring
I was in a different situation. I had the bulbs but my plot wasn't ready yet as I hadn't got around to fertilizing it. So I stuck my bulbs in the fridge for a month to simulate winter, then took them out and split into cloves. I then surface planted then into potting mix, and when the shots were about 5 cm high I transplanted them into the now ready bed. So you could do the same so the plants get a head start without worrying about losing the shoots in a severe frost. Or just plant and mulch with a thick layer of straw.
Fall is traditionally the best time to plant garlic in many regions. A good rule of thumb is to not plant garlic until after the autumnal equinox in late September.