Garlic Growing 101
Site selection, soil nutrients
Garlic is not a fussy crop but also doesn’t tolerate neglect. It works well in most soil types good for general gardening. It does not do well in a continually wet area. If planted in sandy or gravelly soils it will do well as long as you add nutrients (either by amending the soil long term with finished compost, or short term additions of more concentrated organic fertility like bonemeal, bloodmeal, etc) and keep it watered.
pH (the measure of soil’s acidity or alkalinity) is the number one determiner of soil nutrient availability for plants. Aim for 6.5. If you hit 6.5 you are encouraging symbiotic mychorrhizae to colonize the roots and it’ll make extra phosphorus available to the plant- a very good thing. Don’t over-fertilize garlic- I use a gentle 5-4-3 organic fertilizer based on chicken litter but amended with other ingredients, usually applied once in the fall and once in the early spring (around April). If you over-use some fertilizers you can "lock out" one nutrient with an excess of another. Here's a handy chart to get an idea.
Recent research (https://www.uvm.edu/vtvegandberry/AlliumSchool2015/OrganicGarlicFertilityTrialResults.pdf)suggests that the splitting of the nitrogen application is less important than thought. Amending your soil with cow, horse, goat, or sheep manure is a great idea. Chicken manure or litter is good too, but it's higher in fast-soluble nitrogen and shorter in organic matter, which is important for long-term nitrogen availability. Balance is key.
Planting time, spacing, mulch
When to plant? Plant garlic right around your area’s first frost date. That’s something you can Google if you don’t know yet, or check out this link for a basic map - https://bonnieplants.com/library/first-and-last-frost-dates/ . Around my area (White Creek, NY/Bennington, VT) that is October 15th. Up in the Adirondacks and upper parts of New England perhaps think October 1st-7th. Down south, maybe later. It’s pretty forgiving about planting time (go a month in either direction and it will live!) but safest/best results are obtained with that guide. The whole point is for the garlic to have enough time to develop strong roots before winter but to NOT send up top growth of stem and leaf. It will be okay if it does, but better if it doesn't. Plant too late and the root system won't be as vigorous as it should be and you'll get more winter loss.
There are many spacing options for garlic, and it all depends on what your maintenance plan is. You can plant it on a 5 by 5 or 6 by 6 inch grid in a raised bed, you can plant 3 rows 10 or so inches apart, with 4 inches between bulbs. Or some variation thereof. Somewhere around an average of 25 to 40 square inches works. Some magazines will tell you spacings based on single rows but they think you got a tractor or a wheel hoe to cultivate with and a good acre more than you know what to do with. Old data based on single row culture is just not useful in view of modern knowledge about soil health and soil compaction. I do a row system so that applying handfuls of straw mulch is easier (and cultivating with a hoe is easier if I don’t get mulch on in time) but that’s just me. The better and better you get at applying the correct amount of mulch, the more you can move to a denser, more efficient grid system. Think, garlic's roots will grow in a reverse cone downwards, looking like a circle from above. To avoid having roots compete any more than necessary, an equidistant grid is best. A row system is convenient for humans and machines, not necessarily for the plant.
To mulch or not to mulch? Mulching (applying layers of organic matter like straw or tree leaves) around garlic will act as insulation on the soil, protecting from temperature extremes. It will also help keep weeds down. However, once you have mulch on, you can’t get hoes or other tools in for weed control so you’ll have to hand-weed. So, it’s up to you. Less weeding, but all by hand? Or lots of weeding but doable with tools? It also comes down to money, as well. Straw is $5 or $6 a bale, or gathering and applying leaves takes time. Grass clippings are great, too, so that's a way to save money, but takes some time. I have 95% crop survival over winter with mulch, can go down to 85% without. This effect is seen even more with less hardy varieties, where survivability goes from 90% down to 70% sometimes.
I think in the long run mulch is worth it.
Many farmers are switching to black plastic these days, and I've worked on a farm that used it. It certainly works but you should be prepared to have to water the garlic because the black plastic may shed some of the rainwater. Organic mulch is time and money but you're building soil structure every single year and don't have plastic waste that you have to truck off the homestead. The biodegradable black "plastic" mulches made with cornstarch are a good move but though they biodegrade, they don't improve the structure or nutrients the way straw/leaves/grass would.
Also (I know this is a lot of info)...people experiment with new stuff all the time. There is white plastic mulch, some gardeners mulch with newspaper, there's other organic matter out there in your area that may work, et cetera. Many ways to do it right and many ways to do it wrong.
Winter and early spring…
Winter- relax and kick back! Garlic loves to be covered with a layer of snow- that’s nature’s insulation. Don’t worry if it sprouts a bit before snowfall- garlic is nearly impossible to kill by cold.*
*to clarify, extremely cold air or soil temps alone are unlikely to kill it. Most winter loss is from the physical action of "heaving" when unmulched soil thaws into mud at the top couple inches on a warm December/March ish sunny day with no snow cover, only to flash freeze when a polar vortex comes and refreezes the mud (expanding it, due to the water/ice expansion thing), heaving and pushing your garlic around, separating clove from root. Anyways...so...garlic can go down to below 0 and live. What it can't tolerate is massive swings that are like mini earthquakes on the soil level.
Early spring- from mid March to mid April, watch for your garlic to emerge from the chilly soil. It’s one of the most heartening things to see after a long winter. If you mulched it, go out in April and apply bits of extra wherever you need to. If you left it bare, I use April as a time to walk out and hand-pull any weeds I find before they’re well established. It's mostly crabgrass or other hardy perennials that you'll see at this point.
May, June, July- weeding, scape removal, and harvest
Whatever you did for mulch or not, keep your garlic well weeded.* Even in a fertile soil with plenty of nutrients for all, garlic doesn’t want to be shaded or it will mature early and be small. I’ve heard garlic should get an inch of water a week, whether that’s rainfall or irrigation. Frankly when I’ve mulched I almost never turn any form of irrigation on. It’s a sturdy crop and it’s worth remembering its roots go down at least a foot, so a light dry spell is nothing to it. Deciding to water should come down to soil type- if your soil is fast-draining sandy soil you may have to.
*addendum to the weeding comment. My nephew experimented with NOT weeding his straw-mulched patch and it looked about as good as my twice-and-thrice hand-weeded straw mulched field. It's very possible that the weed seeds disturbed and activated by pulling of the first generation caused more trouble than I would have had if I'd just left it all alone. Jury is still out on this!
Scape removal (hardnecks only)- when garlic is approaching final maturation in June into July, it will send up its flowering stalk, called a scape. At the joint of the final, highest pair of leaves, the scape will shoot up from the middle of the stem. It’ll have a strange capsule on the end that will open and set out weak flowers, and form asexual clones called bulbils, if you don’t cut it back. For a larger bulb harvest, you should harvest the scapes before this happens. The scape will form a pig’s-tail curl at first, you harvest it when curled. If not, it will straighten out, and grow tall, sapping nutrients from your developing bulb. You are to harvest the scape about an inch above the final pair of leaves. See here for my video on scape harvest. I let a few go because it’s a magnificent sight, some large Porcelains going to 5 or 6 feet high, but you get small bulbs from those plants. The bulbils are usable as planting stock and will make a tiny round or a tiny bulb the first year depending on their size. They are also edible, but being small, not too fun to work with in the kitchen.
For harvest, you are watching for when the plant’s leaves start to die back. They will turn yellow first, then dry up, lowest leaves first, proceeding to the top. The number of green leaves remaining is roughly how many layers of skin are on your bulb to help it last in storage. Each garlic subfamily is a little different for ideal harvest time. Softnecks (Artichoke and Silverskin family) should be harvested pretty early, when only 3 or 4 leaves have died. Creoles, Asiatics, and Turbans should be harvested when about a 1/3 of total leaves are dead. The rest (all the Purple Stripes, the Porcelains and Rocamboles) can wait til more than half the leaves are died back. Here's a video showing what you're watching for- link
Post-harvest curing- you want your garlic to dry as fast as possible while not letting the bulb sit in the sun to get scorched. Anything that allows that is a good method. On a small scale, making bundles of 5 to 10 plants using twine or string and hanging them under a porch or in a barn works. I lay them in 3 or so layers on benches, slats of wood, or something else with good air circulation due to space considerations. Wire racks work great too!
For planting, there are about a million contradictory pieces of advice you can hear. Grab the whole-est, biggest, shiniest bulbs you got. Grab the busted ones with bad skins. Use this, use that. Here’s the truth- it’s all about economy, disease risk, and thrift. I recommend not planting the absolute largest of your stock because according to the laws of statistics and genetics, there will be a “regression to the mean”- that exceptional stock will eventually return to the genetic average of that species. Even with garlic, an asexually propagated plant, there seems to be an epigenetic imprint given by each season. I have planted beautiful large bulbs and gotten tiny ones the next year. I’ve planted tiny ones and gotten lovely medium and medium-large bulbs. Almost like the millionaire parents who raise a feckless child who squanders the fortune, a huge bulb may imprint on the cloves within the idea that life is easy and they don’t have to try hard. And then that clove grows the next year and makes a supremely mediocre result. As a farmer, I value thrift, so I would rather buy mediums when I am acquiring new stock, and I’ll carefully raise that crop and ideally harvest a better per-bulb yield than the starting seed. If you're willing to spend more money, go for medium-larges, but skip the jumbos, there's just no need, only some of them will be as large as the parents, and many won't be. Save the money and use it for fertility!
As for planting diseased stock- simply DON’T, unless you research how to treat that seed for what it had and know what the problem was.There are organic and natural options for the home gardener to treat infected seed. I haven’t done so yet but I’m looking into it for cases where I may have a blue mold or mite issue. Organic treatments usually involve a hot water immersion (at a specific temperature for a specific time to avoid boiling your garlic!) and/or some use of a light bleach or hydrogen peroxide solution.
Garlic that has lost its skins (by being harvested late or what have you) but looks otherwise healthy, is great planting stock. It won’t be great for storage usually so why not put it in the ground. You should be careful to not have your entire stock come from paperless bulbs though, because you may be slowly selecting your garlic for that tendency. Oftentimes though, it's not the garlic's fault and there won't be any issue with the next generation.
To size your plot, you should become familiar with how many cloves you’ll get per bulb. This varies heavily by variety. You may need to keep anywhere from 1/4th to 1/16th of your harvest back each year just to keep the garlic plot going. If you want to double your crop each year, you’re holding back ½ to 1/8th each year, etc.
Appendix of things I've seen garlic survive:
1. Random garlic cloves falling out of the box and into a highly compacted tractor tire path, and surviving through to harvest the next year as a large bulb. (Proof that all the TLC in the world may not matter, if it simply lands in damn good soil and has no disasters happen to it.) The paths were straw-mulched so it had straw above it, but the clove was laying on the ground and the roots dug in to the earth kind of sideways.
2. An entire section of my garlic garden getting covered 3 inches deep in water that froze solid for 4 months in winter, and then the ice thawed slowly through March and April and shoots still emerged in late April. (Lesson: the soil was not innately poorly drained, mucky soil. It was "okay" soil with a temporary moisture problem.)
3. One year, while working for another farm, while busting bulbs for seed, my boss had us throw away any clove with mechanical damage from being hit with a pitchfork tine- I asked if I could take the damaged ones home. I planted 100 cloves all with pitchfork tine impaling damage...they all came up. And they were all perfectly healthy and made decent bulbs. Basically if the growing tip is there, and the basal plate (the butt) is there, there's a good chance it will survive mechanical damage.
4. A newbie on the farm mixed up what was the top and bottom of the clove and planted their row upside down. 300 row feet of upside down cloves. The garlic knows its gravity and the upper stuff will go up and the down stuff down. It results in crook-necked garlic that is otherwise perfectly healthy.
5. One time I had to have last minute concrete work done and had no choice but to give permission for the cement truck to drive on part of my garlic (in November). It drove back and forth several times on a corner of the garlic patch- some in the direct tire path didn't make it but more than 70% came up, in the heaved ridges, edges, etc, of the tire paths.