I don't know how garlic grows in Arizona, but the general rule for harvest is when about half of the leaves are yellow/brown, or if you prefer, when only about 3-4 green leaves remain. Garlic often falls over before this stage. If yours are still mostly green, I would leave them in the ground.

Here in NJ, harvest comes from late June to mid July depending on the variety of garlic. Grocery store garlic is usually a softneck artichoke type, which mature earlier than hardnecks. I would expect harvest to be earlier in your warmer Arizona climate, but April seems too early to me.

You might want to pull one to see how the bulb is developing.

TomNJ

Andy, it is way too early to harvest your garlics now. Probably they will be ready by late June or July. I have planted mine last October(in Z 8) and I should be able to harvest them in June. Yesterday I dug one out to use as green. No bulb there yet. It looks like leeks at this point.

Won't be harvesting the earliest of the garlic until the middle of June here, but the gophers have broken into my largest raised bed and are doing some of their own harvesting as we speak. So far I am only down a dozen or so plants, but know they will take the rest of them before they are ready to harvest.

This is great info to know, as the same thing is happening to some of my garlic. 4-5 of the 10 or so I planted in the late Fall last year have about half their leaves turning brown.

Keep watering and fertilizing and be patient. Fall planted garlics (OCT-NOV) will not be ready before mid June or there about.