Every year at about this point in the growing season, Alley Swiss has a ritual he performs. It’s one that humans have done for thousands of years, as they cultivated one of our oldest, most beloved food crops.

Mr. Swiss, an organic farmer, walks out into his garlic field in the Okanogan Valley of north-central Washington, looking for guidance: Is the garlic ready?

Harvest has already begun in the South, the Gulf States and lower-elevation areas of the Southwest. “But pretty much coast to coast in the North, it’s usually mid-July,” Mr. Swiss said, with some varieties requiring even more patience.

But he doesn’t simply look at the calendar and start digging. He watches, and he waits. If you know how to look, he said, the garlic will tell you when it is time.

Mr. Swiss has been growing garlic in this semiarid zone an hour below the Canadian border for 10 years, since he and his wife, Phoebe Swiss, took over one of the oldest certified organic farms in the state of Washington. Filaree Garlic Farm has been certified since 1978, and garlic has been grown there for about 35 years, with 30 acres — a projected harvest of some 20,000 pounds — currently about to come due.

All of it will be sold as “seed garlic,” as the bulbs are called, not to restaurants or groceries. Of course, they’re not seeds, exactly. Each clove tightly packed within a head is popped out and planted separately by Filaree’s customers, most of whom are home gardeners. (About 20 percent of sales are to commercial growers and garden centers.)

But growing and selling seed garlic isn’t the only thing that Filaree Garlic Farm does. With more than 100 varieties in its collection, it has a responsibility that many of its customers may not realize: It acts as a seed bank for garlic genetics from around the world.

Today, wild garlic is found only in parts of Central Asia, but it may once have grown wild from China to India, Egypt and Ukraine, according to Philipp W. Simon, a research leader at the Agriculture Department’s Agricultural Research Service and a professor in the University of Wisconsin-Madison’s department of horticulture. From those ancient beginnings, garlic has traveled the globe to become one of the world’s most important vegetable crops.

“The varieties we grow are really the work of cultures who have been growing and selecting them for thousands of years,” said Mr. Swiss, whose catalog lists varieties like Romanian Red, Thai Purple, Sicilian and Transylvanian. “Garlic was something people could take with them while traveling from area to area. They could plant it where they ended up, and the garlic evolved as they did that.”

Garlic asks for an investment of time, going in the ground in fall and remaining there until the following summer. But Mr. Swiss is in no rush, and Filaree’s other specialties include organic asparagus crowns, sweet potato slips and seed potatoes — all vegetative rootstocks that, like garlic, are carefully stored from year to year as future “starts.”

Business in this pandemic year has been brisk at Filaree, as it has been for most suppliers of the raw materials of food gardens. “When you’re surrounded by so much economic devastation,” Mr. Swiss said, “doing business feels awkward. But we’re happy people want to grow food.”

He shared his knowledge on harvesting, curing and storing garlic — and how to plant this fall as an investment for years to come.

Hardneck or Softneck?

There are two principal types of garlic: hardneck and softneck.

They’re grown the same way, but one has a bonus harvest. Hardneck varieties produce delicious scapes, or seed stalks, two to four weeks before the bulbs are ready. Scapes should be removed, and they make great pesto that can be frozen; they can also be sautéed or grilled.

About two-thirds of Filaree’s field comes out in July, but the latest-to-mature are softnecks called silverskins, which are harvested as late as early August. They are the most common type sold in supermarkets, because of their long storage life.

“We plant our field chronologically, so we can work from one side to the other at harvest,” Mr. Swiss said. “Though weather does play tricks, so it isn’t always as precisely organized as that image lays out.”

Read the Leaves

That’s how you’ll know when to harvest.

As July approaches, Mr. Swiss has his gaze on the garlic leaves. When four or five green leaves remain close to the top of the plant, and the rest are near crispy-brown with no green left, then you are within harvest range. “At that point, take a couple of samples,” he said. “Dig a bulb and take a peek — which, after waiting eight or nine months, is such fun.”

Notice he didn’t say pull, but dig, or at least loosen the soil with a spading fork at a safe distance from the bulbs, before lifting the plants.

What is Mr. Swiss looking for? “I look for mature bulb development in the ‘shoulder,’ where the bulb curves toward the stem,” he said. “There should be clear definition between neck and bulb; an immature bulb simply curves into the neck.”

The shoulder develops in the last few weeks before harvest, as the bulbs swell in the summer heat.

Weather, however, can upset the natural order. When conditions are too wet close to maturity, it can cause issues with bulb-splitting and rot. “I might jump the harvest and start at six green leaves,” he said. “But I don’t go past four, even if it’s very dry.”

That’s because garlic left in the ground too long is prone to deterioration of the bulb wrappers — the lower portion of the leaves — and it’s also prone to rot.

And while garlic dug before full maturity, or left too long in the ground, may still be edible, it won’t cure or keep as well.

Curing the Garlic

After the harvest, hardneck plants — untrimmed, but cleaned up — are hung in bundles in the barn. Softneck plants are cured on racks, because plants may slip out of knots made to bundle and hang them.

Whatever the setup, there are three crucial ingredients for curing, Mr. Swiss said: “Airflow, relative darkness and heat — those three factors will affect the quality of the garlic and the length of time it stores.”

Gardeners with no outside shelter can lay plants out in a relatively dark room on a rack made of screening or hardware cloth, with airflow below and a fan directed on the bulbs.

“In optimal conditions like our hot, dry summers here, curing takes only two or three weeks,” Mr. Swiss said. “But it can take longer. If you’re in a humid place, the fan goes a long way.”

Bring the Temperature Down

Heat is important for curing, but when you’re storing garlic, you’ll need to cool things down.

After curing, trim the dried roots and stem, and peel off the dirty, outermost layer if you like, but leave the lower portion with at least four of the old leaves on. Each leaf is a bulb wrapper, and the more wrappers, the better storage.

The ideal storage conditions are cool and dark, and neither too humid nor too dry — about 50 degrees and around 65 percent humidity.

You can store garlic in temperatures as low as 38 degrees, Mr. Swiss said, but there will be consequences: “Once you take garlic out of that temperature, it sprouts quicker than bulbs stored closer to 50, because you’re playing with plant’s vernalization cycle.”

In other words, the bulbs perceive that they’ve been through winter and that spring has arrived, so they wake up.

A Primer on Planting

Hardneck and softneck bulbs should be planted in a sunny spot with well-drained soil, three to five weeks before frost is in the ground. In frost-free zones, plant in November or December.

The biggest cloves yield the strongest plants, so plant those. (The smaller ones, you can eat.)

Plant in a grid, placing each clove root side down (point up) about two to three inches below the soil surface, with cloves spaced five to eight inches apart in all directions.

The key is making sure you have enough room between rows to cultivate and weed, because garlic does not compete well with weeds, especially early in its growth. A layer of mulch applied after planting helps suppress the weeds. (More information on growing garlic, and the varieties that best match various regions, is available here.)

And maybe most important: Remember to plant plenty of garlic to cure and store, because you’ll need more than just what you’re going to eat. If you want future crops, you’ll need something to replant.

“There are not many vegetables where saving seed is as straightforward,” Mr. Swiss said. “By simply setting some bulbs aside to put back in the ground in fall, you get to participate in an act both ancient and with hope for the future.”

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