It happened faster than seemed right. One day, the tiny gray pinheads of mushrooms were just beginning to emerge from a two-inch cut in a bag of sawdust; the next, they were huge, scalloped hand-like lobes. They looked practically in motion, like muscular forearms reaching out of a wormhole.

It was early summer and I was growing blue oyster mushrooms on my kitchen counter. It was more dramatic than I could have imagined.

It started out benignly enough. About two months into lockdown, the ecology of my Instagram feed began to shift away from sourdough bread and toward mushroom grow kits. These kits are blocks of compressed waste from sawmills, which have been implanted with the mycelium of wood-eating fungus. (Mycelium are the fine, hairlike tendrils that are the principal part of any fungus; mushrooms are merely the fruiting parts — similar to apples on a tree.)

The mycelium, delighted to find themselves nestled in a cocoon of their favorite food, grow threads, digesting sawdust as they go, probing for a bit of air and moisture, which they cannot find, because the blocks are encased in plastic bags.

That is where the fungal gardener comes in: If you cut an X in the plastic and spritz that X with water a few times a day, the mycelium will find their way to that spot, communicating across their many tendrils to coalesce into solid flesh, and will burst forth as mushrooms.

Sacks of sawdust filled my friends’ counters, each frothing over with bulbous lion’s mane or disgorging scaly oyster mushrooms. The kits for growing pink oysters, which emerge as a cascade of salmon shingles, were particularly photogenic.

I called two mushroom farms that had supplied the bulk of my friends’ kits and learned business was booming. “It’s been a very steep increase in sales,” said Matt McInnis, one of the founders of North Spore, in Portland, Maine, which was started in 2014 by three friends who went mushroom foraging together in college. Sales of introductory mushroom growing supplies had increased 400 percent during the pandemic over the previous spring, he said.

Smallhold, a farm in Brooklyn that had previously supplied restaurants with mushrooms and installed mini mushroom farms in commercial kitchens, also had a spike when it pivoted to at-home mushroom kits as restaurant orders dried up, the farm said. Customers tagged Smallhold in endless posts of sculptural mushroom clusters that emerged, somehow, nearly overnight.

“Mushrooms are mysterious and ephemeral,” Andrew Carter, 35, a founder of Smallhold, had warned me before I took my kits home. He said they were more like growing animals than plants, but not quite that either; after all, fungi are a kingdom of life all their own. “They may not look like anything for a while and then all of a sudden there’s mushrooms,” he said. “It’s unlike anything people have seen.”

Trendy Trash Monsters

Across Asia, mushrooms have long been prized, for food and flavor, medicinal and ritualistic purposes, and in poetry and prose. Rich mushroom foraging traditions have been passed down for centuries in several parts of Europe as well, where going to a forest on the weekend to pick mushrooms is still a common family outing. In France, virtually every town has its own mushroom expert, trained by the government.

Colonizers brought these traditions to the Americas, where Native American people had also been eating foraged mushrooms forever. In regions like Appalachia, wild mushroom hunting — particularly for morels — remains part of the rural foodways.

And while urbanites tending mushrooms in cramped apartment kitchens may seem a far leap from those traditions, their interest in fungi — along with the continuing rise of meat-shunning diets — is a small component of a global passion. Mushroom import and export is an enormous worldwide business, with the mushroom market expected to reach $86.6 billion by 2025, according to the market research company IMARC.

That passion may also have to do with new applications of mycelium, and novel research into its seeming world-saving potential.

Fungi thrive on waste and decay. They are, in essence, trash monsters, making value out of chaos. “Mushrooms are decomposers,” Mr. McInnis, 33, said. “If you provide them with an opportunity to consume something they will.”

And they’ll do it fast: Crops of mushrooms are known to emerge fully formed overnight, sometimes pushing up unthinkably heavy loads of earth and pavement in the process. No one yet knows how it is possible for a soft thing to heave so much.

Beyond decomposing dead organisms (like rotting trees, or waste from sawmills, as is the case with the at-home kits), they can infiltrate almost anything, chewing through rock, plastic and even radioactive materials. Some species have shown promise in cleaning up environmental waste sites, happily digesting toxins and blooming into benign fruit.

There is renewed scientific investment into many compounds found in mushrooms, including psilocybin, which has shown promise for treating depression in clinical trials. Lion’s mane, an edible (and non-psychedelic) mushroom, is believed by many consumers to be good for the brain, and a study published in 2011 showed the mushroom reduced memory loss symptoms in mice.

It remains to be seen if those results could translate to humans, but one study in older people found that daily lion’s mane supplements improved their mental functioning. (“Lion’s mane is having a real moment right now,” Mr. McInnis said. “It’s our best seller.”)

In a world where the construction industry produces more than one-tenth of all greenhouse gases, fungi may become a sustainable building material; mycelium grow obscenely quickly and can be coaxed to take the shape of architectural molds. So far, tinkering researchers have managed to guide it into the form of compostable bricks and rather organic-looking chairs. Some fashion designers are also experimenting with mushroom leather.

In the late 1990s, the biologist Suzanne Simard published a paper detailing how trees in a forest can exchange nutrients by way of underground mycelium. Since then, researchers have found that fungi so thoroughly infiltrate the roots of most every plant in the wild that they are inextricable from the plants themselves.

They serve as a brokers of vital nutrients, and in some cases may be responsible for the very traits that define the plant species, like the sweetness of a tomato or the ability of a coastal grass to tolerate salty water. Some research suggests fungi entwined in tree roots may even serve as information highways, passing information about threats between trees.

The possibilities feel endless, and provoke a certain mysticism in the mycologically minded: “The more you talk about mushrooms, the more you want to talk about mushrooms,” said Mr. Carter, of Smallhold, grinning a little. “Some people think that’s by design, as a way to spread their spores.”

A 2008 TED Talk by the renowned mycologist Paul Stamets, on the properties of mushrooms, has been viewed nearly three million times. In 2015, Anna Tsing published “The Mushroom at the End of the World,” which contemplates fungi’s role in the ruins of capitalism; it proved to be a rare academic book that managed to cross over into the popular market.

More recently, the documentary “Fantastic Fungi,” released in 2019, espoused the wonders of the below-ground fungal kingdom normally hidden from view. It was narrated by the actress Brie Larson, embodying the role of an omniscient mushroom.

Smallhold, which opened in a shipping container in the Williamsburg neighborhood of Brooklyn in 2017, has seen the sudden interest in fungi firsthand; in three years, the company has grown to 25 employees from two, and is still hiring. That’s likely linked, in part, to an expanding interest in eating mushroom varieties beyond the kind found in grocery stores: For decades, the only mushrooms the average consumer in the United States had access to were button, portobello or cremini varieties.

All three are actually the same species, just at different stages of growth. “It’s an illusion of diversity,” Mr. McInnis said. In a kingdom that contains more than a hundred thousand known species (the total number is likely to be several million), of which some 3,000 are edible, this amounts to a monoculture, not unlike our overreliance on just a few varieties of grains and vegetables.

The sudden interest in at-home mycology, specifically, seems to have a particular resonance with our times. In our ruined global moment, watching something busily transform trash into fleshy, sculptural, delicious fruit is a comfort, so it’s little wonder they’ve become popular in a pandemic.

In my apartment, once the cycle began, it didn’t stop for weeks. Every five or six days, one of my six mushroom kits would disgorge a pile of fleshy appendages, always faster than seemed reasonable. Each time I was newly shocked.

Six kits for two people quickly proved an outrageous excess. We had pounds and pounds of mushrooms to consume. I cooked oyster mushroom bourguignon, mushroom tacos, mushroom pastas. I sliced the bulbous lion’s mane into thick steaks and seared them in butter. When a few mushrooms sat out too long and shriveled, I boiled them into a mushroom stock for ramen. It was incredible. Still, we could barely keep up.

A Most Promiscuous Nature

As sourdough bakers know, any given room is already full of fungi spores (yeast is fungi; the diversity of yeasts in the air that come to colonize a sourdough starter will result in a distinct flavor of bread, a sort of fungal terroir).

This promiscuous nature means that fungi grow rooms must be kept sterile to avoid cultivating unwanted crops, a condition that lends itself well to a pandemic. “It’s a very clean process already,” Adam DeMartino, 36, Smallhold’s other founder, said. Smallhold farmers wore personal protective equipment even before the pandemic.

I took no such precautions growing fungi in my home. I watched, concerned, as a seemingly unrelated population of fungi produced orange bubbles on the surface of one of the Northspore kits before it had managed to put out any mushrooms. But within 24 hours the struggle for dominance appeared to resolve; the foreign fungi — perhaps a colony of wayfarers from the bag of golden oyster mycelium beside it — was gone, and pink oysters began to emerge.

One morning, sometime between the first and second crops, or flushes, of blue oyster mushrooms, I wanted to make a coffee scrub. (A fantastic thing — you mix spent coffee grounds with olive oil and slather it on in the shower. You come out feeling like a newborn seal.) I dumped the grounds from my morning espresso into a bowl on the counter to dry. I added more grounds the next morning, and then forgot about my plans. The bowl sat on the counter unattended.

A few days later, I noticed orange foam was burbling up within it. It was the same orange tint as the growths on one of the mushroom kits sitting on the opposite counter. Spores from the golden oysters had floated through my kitchen and landed on extremely suitable ground(s).

I was front row to a fungal safari. There were invisible exchanges — infestations — happening without my knowledge or consent.

This was the most action my apartment had seen in months. I felt proud that spores might find various hospitable substrates around my home: the grout in the kitchen tile, a musty corner of my old wood floor, the unfinished pine boards stained with water rings from the places I’d set down potted plants too soon after a watering. Fungal threads, for all I knew, could be probing, tendrilic, just beneath the surface right now. They might emerge and sporulate, as the kits had done, sending microscopic sentinels zooming around the room.

Sporulate: It’s a revolting word, but it is also erotic. (Revulsion and desire are not always so far apart.) Sporulation is, after all, fungal sex. The word suggests penetration, fertilization, mingling in places dim and dank. I always suspected my prewar apartment to be in a state of perpetual crumbling, but this was a new element. Add fungi, and it might not merely crumble — it might be gleefully decomposed.

My home wasn’t just the site of a mushroom orgy, it was a participant. I hoped fungal bodies would fruit from my walls and cascade from the fixtures.

Alas, this did not happen. My partner, unaware of my experiment, dumped it in the compost. I was comforted by the thought that the fungi would likely find a way to flourish at the local community garden compost heap, to turn the coffee into a rich black dirt by way of its own body, perhaps becoming the substrate for a seed to take root and emerge a tree — which would, inevitability, become the food for some other lucky fungi. The cycle of birth and decay would roll flamboyantly onward, eating itself alive.