Fall is the correct time to plant garlic in the south. It comes up and grows through the winter and is ready to harvest in late spring to early summer. I planted mine 3 weeks ago and I would guess that 2/3 of it is up now. After getting the soil prepped, I laid 2 x 4 lumber on the soil where the rows would be and mulched the entire bed. Then I pulled up the lumber and planted the garlic in the blank spaces. Naturally, the pine straw kind of "dripped" over the row areas, but the garlic seems to be coming up just fine. Chances are that your freeze tonight will not harm your garlic whether you mulch or don't. They are only calling for 30 here.... If you are concerned, though, I think the easiest thing to do would to be just to throw some row cover or even a sheet over the plants for the next two nights. It's not supposed to be freezing for at least another week after that.

The main reasons to mulch garlic are weed prevention, and soil temperature stabilization. Ideally, the mulch insulates the ground long enough to allow the cloves to develop some root growth before the ground freezes - which helps prevent frost heave. The insulation provided by the mulch also prevents premature sprouting during early warm spells in Spring. Rocks might reduce weeds somewhat, and the garlic should push through (unless the rocks are large) but rocks are poor insulators. I get a few very windy days here too, and would recommend mulching with dried alfalfa (if you can get it), or an alfalfa/hay mix. Bales are not hard to come by here, and I found quite a few current Wyoming sellers here. Alfalfa binds together well when spread in a layer & wetted down. Clover hay would be my second choice.

Good advice, pine needles are acidic the lime won't hurt, and will mature (which it does slowly) to be also available to second season crops once the garlic is harvested. I got caught short on time and energy this autumn or I would have prepared beds for next years tomatoes and peppers, and limed them. That fall lime seems to me to keep blossom end rot to a minimum. Mulch for garlic has to be the sort that does not pack down over winter, since the new shoots have to come up through it. I don't always fall mulch my garlics. This year it didn't get done, not last year either, and I had almost perfect stands last spring anyway. It will be even more effective to spring mulch to keep soil moisture uniform for best top growth. Once again summer mulch also has to breath since garlic required good drainage.

Phil, Up there in Canada, you mean zero Centigrade right? Most of us in the USA read temperature as Fahrenheit. For you if zero means above freezing, which for us would be 32, well you don't have to wait for that. Garlic is hardy here in Minneapolis to well below -20 F or which is just about -30 C. Temps around the freezing mark a bit either way don't bother garlic much if at all provided drainage is good. Garlic goes through that around here every spring with no problem whatsoever. I did not mulch last fall either and both my garlics and my walking onions are up with new growth showing in the middle of what was left from last falls growth. As for the mulch I would leave it alone, just make sure it is not packed down tightly enough to keep the garlics from poking through it. I would only remove the mulch, if the ground needed the extra air circulation to prevent the garlics from rotting. (But IMO you should have made arrangements for drainage when you set up the bed to plant last fall. I had to learn that lesson the real hard way, by losing an entire planting of expensive new stock!) If you have any garlics poking through and in zone 6 you probably do, it is probably nothing to worry about any more. Here in Minnesota I probably should mulch my garlics now as soon as the ground is well thawed because this spring threatens to be quite dry and the mulch would help hold the moisture. BTW we have no snow cover and no forecast for any in the foreseeable future, but I will take all the rain I can get right about now.