Common Myths About Mushroom Farming, Busted: What Really Happens Behind the Farm Door

By CJ's Mushroom Farm | Marasandra Village, Bengaluru Rural, Malur Taluk, Kolar District, Karnataka.

Do mushrooms really grow on manure? Do they need sunlight? Is a longer shelf life a sign of quality? Mushroom farming is surrounded by myths, and most of them fall apart once you see how a mushroom is actually grown. In this post, we bust eight common myths with research-backed facts and a look at how we are building CJ’s Mushroom Farm.

Myth 1: "Mushrooms are grown on manure, so they must be dirty"

This is probably the most common myth, and it comes from half a truth. Button mushrooms (Agaricus bisporus) do grow on a specially prepared compost, and manure is one ingredient in it. But the compost is a carefully engineered growing medium, and it goes through a process designed to make it safe and selective for mushrooms.

Commercial compost is made in two phases. In Phase I, microbes break down the raw materials and generate a lot of heat by themselves. Research at Penn State has recorded temperatures above 80°C in Phase I composting. In Phase II, the compost is moved into a closed, controlled space for pasteurization and conditioning. The goal is to free the compost of unwanted organisms such as insects, nematodes and harmful microbes. A Penn State food science study on manure-based mushroom substrate found that a standard Phase II process can be an effective control measure for human pathogens. Phase II also gets rid of ammonia, which is toxic to mushroom mycelium. Helpful microbes convert it into microbial protein.

At CJ's Mushroom Farm, our compost is built on wheat straw, chicken manure, oil cake, seed hulls and gypsum, along with small amounts of nutrient and mineral supplements in a carefully balanced, proprietary blend. In our outside bunker, we observe the compost heating itself up to about 72–76°C through natural microbial activity. It then moves to a closed pasteurization tunnel with no external heating source, where controlled pasteurization and conditioning are designed to reduce harmful pests, pathogens and weed seeds. Our composting is usually done in 13 days. When raw materials are low in moisture or the sun is strong, we extend a phase by 2–3 days so the compost is ready by day 15.

You can read the full story in The 15-Day Composting Secret.

A final honest note: a clean growing medium is only one part of food safety. Hygiene across the whole chain matters just as much, as we explain in Chemical-Free Doesn't Mean Zero Risk.

Three-step infographic showing compost heating itself in an outdoor bunker, moving to a closed pasteurization tunnel with no external heating source, and being ready for spawning by about day 15.

Two-panel illustration showing white button mushrooms grown in the dark in a growing room, then selected top-grade mushrooms exposed to UV light in a separate chamber after harvest.

Myth 2: "Mushrooms need sunlight to grow"

Plants need sunlight because they photosynthesize. Mushrooms don't. Fungi have no chlorophyll, and they get their energy by feeding on organic material. University extension guidance confirms that fungi can grow in complete darkness. That's why commercial white button mushrooms are grown in dark, climate-controlled rooms. At our farm, we grow in the dark too.

Light isn't entirely irrelevant for fungi. Some species use it as a signal to orient their growth or start fruiting. But for a button mushroom, light is not an energy source. Sunlight is simply not what a button mushroom grows on.

Where UV does come in is after harvest. Published research shows that when mushrooms are exposed to UV light, a compound in their cells called ergosterol converts into vitamin D2. A major 2018 review in the journal Nutrients found that UV-exposed mushrooms can generate nutritionally relevant amounts of vitamin D, while the same review notes that an ordinary serve of unexposed mushrooms provides very little. At CJ's Mushroom Farm, UV exposure is a separate step. Selected top-grade mushrooms are exposed in a dedicated UV chamber after harvest, not during growing.

Everything we say about vitamin D is based on published research. Independent lab testing of our own harvest is still pending, and we will share results when we have them.

To understand the science, read The Sunshine Vitamin: Why Mushrooms Are the Perfect Plant-Based Powerhouse, Vitamin D: The Sunshine Nutrient and Your Health, and Farm Fresh vs Vitamin D Enriched: Which One Should You Choose?

Myth 3: "Mushroom farming needs acres of land"

Mushrooms grow up, not out. Beds are stacked in racks inside growing rooms, so a small footprint can produce a lot. A sustainability study commissioned by the US Mushroom Council reported an average annual yield of 7.1 pounds per square foot, partly because beds are stacked vertically. An Indian Council of Agricultural Research (ICAR) review also notes that mushroom production, grown in racks indoors, needs comparatively little land. Mushrooms use agricultural waste like straw as their growing medium, and they need less land, water and capital than many crops.

This is good news for small and marginal farmers, and it is part of why we believe every region can have its own small-scale mushroom farm. For the story of how we use vertical space, see Farming Vertically: How We Grow More Mushrooms on Less Land.

Cut-away illustration of a compact mushroom growing house with stacked racks of white button mushrooms, contrasted with the outline of a large open field.

Myth 4: "Farm-grown mushrooms are 'forced' or artificial"

Growing mushrooms indoors can sound unnatural, but fruiting is a natural response to the environment. A scientific review of how Agaricus bisporus starts forming mushrooms describes the critical factors as a drop in temperature, a drop in carbon dioxide in the growing room air, and the breakdown of a natural volatile compound the fungus itself produces to inhibit fruiting. Separate research shows that temperature reduction drives the later development of the tiny mushroom buds, while carbon dioxide level influences how many fruiting bodies form.

In other words, the mushroom is responding to environmental cues, much like it would in nature. A farm that manages temperature, humidity and fresh air is giving the fungus those cues on a reliable schedule. It's closer to a greenhouse than a laboratory. If you're curious about the bigger picture of how we think about sustainable growing, read How Mushrooms Are Grown: A Behind-the-Scenes Look at Sustainable Farming.

Myth 5: "Mushrooms are just vegetables with no real nutrition"

Mushrooms are used like vegetables in the kitchen, but biologically they are fungi, a kingdom of their own. Fungi are genetically closer to animals than to plants.

Nutritionally, food composition data for button mushrooms list potassium, selenium and B vitamins, along with a modest amount of protein, at very low calories. The exact figures vary between databases and growing conditions, so we avoid quoting a single number here. What we can say is that mushrooms are far from empty food. Vitamin D is the special case, because unexposed mushrooms provide very little. That's the reason UV exposure matters in published research and why we treat our UV-exposure step as a separate, carefully handled stage. For why we chose this particular variety, read Why Button Mushrooms? The Science Behind Choosing This Variety.

Myth 6: "A longer shelf life means a better mushroom"

Fresh mushrooms are among the more perishable foods in your kitchen, and science explains why. Reviews of postharvest biology describe a very high respiration rate, high water content and no protective outer layer to prevent water loss. This is also why browning and spoilage show up quickly.

Methods exist to extend shelf life, from modified-atmosphere packaging to coatings and washes. But a longer shelf life doesn't automatically mean a fresher or better mushroom. It can simply mean a longer time between harvest and your plate. Our approach is built around daily harvest and same-day delivery to retailers, with no cold storage, so freshness reaches you while it counts. We explain this philosophy in Why Farm-Fresh Mushrooms Have a Shorter Shelf Life, and Why That's a Good Thing. And when you're at the store, our Farmer's Checklist will help you spot a genuinely fresh mushroom.

Illustration of a white button mushroom at the button, cup and flat stages, showing they are one species at different stages of maturity.

Myth 7: "Button, cup and flat mushrooms are three different mushrooms"

White button mushrooms, cremini (often called baby bella) and portobello all belong to the same species, Agaricus bisporus. They are essentially the same mushroom at different stages of maturity. Buttons are harvested young, before the cap opens. As the mushroom matures, the cap expands, flavor becomes more developed, and the texture changes. Some brown-capped varieties are different strains, but the species is the same.

At CJ's Mushroom Farm, we grow only white button mushrooms. If you want to know how a single mushroom behaves in the kitchen at each stage, our post One Mushroom, Every Stage: A Cook's and Scientist's Guide to Buttons, Cups & Flats goes deeper.

Gloved hands mixing dark, crumbly compost into garden soil beside healthy green seedlings.

Myth 8: "Once harvesting ends, the compost is just waste"

After the mushroom crop is done, what remains is called spent mushroom substrate or spent mushroom compost. Penn State Extension describes it as high in organic matter, which makes it useful as a soil amendment and conditioner. It mainly improves soil structure and provides a few nutrients. The same guidance recommends using substrate that has weathered for several months in most gardens, because fresh material can carry higher levels of soluble salts that stress seedlings and salt-sensitive plants.

So spent mushroom compost is best seen as an organic soil amendment, one that returns organic matter to the soil and closes the loop on the farm. It's not a miracle product or a complete fertilizer, and it should be used sensibly. To use it well, read Spent Mushroom Compost 101: What Every Gardener Should Know Before Using It and Black Gold: Compost After Mushrooms Are Gone.

Summary graphic listing eight common mushroom farming myths with a short factual correction beside each.

Why we're busting these myths

We are a young farm in its development stage, and we believe trust is built by explaining things openly: what we know from published research, what we do on the farm, and what we are still testing. Mushroom farming isn't magic, and it isn't dirty or artificial. It's biology, patient process and careful hygiene working together.

Follow our journey

Want to see how it all comes together? Visit cjsmushroom.in to learn more about our farm and our White Button Mushrooms, watch our farm stories on our YouTube channel, and follow our day-to-day progress on Instagram, LinkedIn, and Facebook as we build toward our first harvest.

Disclaimer: CJ's Mushroom Farm is currently in its development stage. Nutrient and microbial claims discussed in this post, including those about our compost process, are based on published research and remain pending in-house research and independent laboratory testing of our own harvest.

References

For readers who want to dig into the research behind the claims in this post — full credit to the original authors:

Standard Phase II composting as a control measure for human pathogens in manure-based mushroom substrate: Inactivation of Human Pathogens during Phase II Composting of Manure-Based Mushroom Growth Substrate, Penn State Department of Food Science.
Phase I temperatures above 80°C, and the objectives of Phase II pasteurization and conditioning: Phase II pasteurization conditions during substrate preparation for Agaricus bisporus (Microbial Ecology study), UNESP institutional repository.
Pasteurization of insects, nematodes and pathogens, and conversion of ammonia into microbial protein in Phase II: Tom Volk's Fungus of the Month for April 2001: Agaricus bisporus, University of Wisconsin–La Crosse.
Definitions of pasteurization and Phase I and II composting: Common Terms, American Mushroom Institute.
Fungi as heterotrophs that can grow in complete darkness, and fungi's closer relationship to animals than plants: A Beginner's Guide to Growing Mushrooms at Home, Utah State University Extension.
Button mushrooms commonly grown in the dark, with light used as a signal by some species: Do Mushrooms Need Light?, GroCycle.
UV conversion of ergosterol to vitamin D2, and negligible vitamin D2 in an ordinary serve of unexposed mushrooms: A Review of Mushrooms as a Potential Source of Dietary Vitamin D, Cardwell et al., Nutrients (2018).
Average annual yield per square foot and vertically stacked beds: The Mushroom Sustainability Story, Mushroom Council.
Indoor rack-based mushroom production needing less land, water and capital: Status of mushroom production: Global and national scenario, Mushroom Research 32(2), ICAR.
Temperature drop, CO2 drop and a volatile self-inhibitor as critical factors in fruiting: Critical Factors Involved in Primordia Building in Agaricus bisporus: A Review, Molecules, MDPI.
Temperature reduction for primordia development and CO2 control of fruiting body number: Environmental regulation of reproductive phase change in Agaricus bisporus by 1-octen-3-ol, temperature and CO2, Eastwood et al.
Button mushroom food composition (potassium, selenium, protein, vitamins): Button mushroom nutritional sheet, Aprifel.
Short postharvest life from lack of a protective cuticle, high water content and high respiration: Damage and Browning in Edible Mushrooms (Agaricus bisporus), Iranian Journal of Plant Biology.
Respiration rate as the main limit on button mushroom shelf life, and modified-atmosphere approaches: Effect of short-term high CO2 treatment on quality and shelf life of button mushroom (Agaricus bisporus) at refrigerated storage, Journal of Horticulture and Postharvest Research.
Coatings and washes as shelf-life extension methods: Effects of Calcium Salts on Browning of Edible Mushroom Caps, Iranian Journal of Plant Biology.
Button, cremini and portobello as one species at different maturity stages: What's the Difference Between White, Baby Bella, and Portabella Mushrooms?, CulinaryLore.
Same species, different stages of maturation: Baby Bella Mushrooms: Everything You Need to Know, Fine Dining Lovers.
Spent mushroom substrate as a high-organic-matter soil amendment, and weathering before garden use: Spent Mushroom Substrate, Penn State Extension.
Soluble salts in fresh spent mushroom substrate: Spent Mushroom Substrate as a Component of Soilless Potting Mixes: Nutrient Changes During Composting, Penn State, via Forest Nursery Notes.

Note: These references support the general scientific principles discussed above (composting and pasteurization, mushroom biology, UV and vitamin D research, postharvest physiology and spent substrate use). CJ's Mushroom Farm has not yet conducted independent lab testing on its own harvest — that's planned for after our first crop cycle.