I usually harvest mine in July.

Where do you get that DTM? My garlic matures any time from late May to mid July, depending on the variety, so I guess 90-150 days from resumption of spring growth (about the end of February around here) could be about right.

Some varieties started growing in November, while others basically sat still until February, though all were planted about the same time. Bulb formation is also affected by day length, so any DTM is going to be subject to many variables it seems to me.

Cara, like daffodils and tulips, garlic is tied to the rhythms of the changing seasons. In the dry Mediterranean regions from which it came, its survival was insured by going dormant from midsummer to late fall, the dry season. Soil moisture cycles, temperature changes, and day length combine to trigger various phases of the garlic life cycle. You can't therefore change its planting dates and expect success. Plant in fall or early spring, because that's how garlic knows how to grow.

Burpee lists DTM for most varieties as 90-150. Gurneys lists it as 120+.

I'm not thinking about changing the cycle, just trying to figure out how to plan the garden. I was trying to figure out if I could cycle continually plantings (plant spring, harvest in fall, replant for fall, harvest spring, replant for spring), but it sounds like the fall planting would mature too late to replant for spring.

I think the best you could do is extend the season a little with overlapping plantings. One in the fall for early summer harvest, the other in the spring for late summer harvest. You might want to follow garlic with fall greens and/or brassicas. In my zone I had time to grow a crop of cukes after the garlic came out.

Garlic stores so well that one planting can provide a year's supply. Also, when garlic matures, it becomes dormant for 3-6 months and will not sprout. You can plant different types (early and late) to split up the harvest, but because the curing process requires attention, harvestiing the crop all at once has its advantages.

Planatus is right. I plant once and have garlic til the next crop, with some left over. And curing is important and being careful not to bruise also. I think temperature seems to trigger when it is time to harvest. as it seems to vary from year to year.