How Fast do Mushrooms Grow – The Fastest Mushroom Included

Mushroom growth speed depends on the species and conditions, but most edible varieties grown at home reach harvestable size within 3 to 7 days of pinning (the point when tiny mushrooms first appear).

Oyster mushrooms are the fastest and most beginner-friendly cultivated species, colonising a substrate in 10 to 12 days and producing harvestable flushes within a week after that.

Wild mushrooms often appear to grow overnight because they develop rapidly in warm, humid conditions, and their small early-stage size makes them easy to miss until they reach a noticeable size.

This guide covers how mushrooms grow, how fast different species develop, what conditions accelerate or slow growth, and how to get started growing your own.

I grew my first mushrooms in a spare bedroom using a basic oyster mushroom kit bought from a garden centre, not knowing what to expect from the timeline.

The speed surprised me: within two weeks of setting it up there were harvestable mushrooms, and the second flush came ten days after that.

The whole process felt unlike growing any other food because the biological mechanisms are so different from plants.

Understanding what a mushroom actually is, and how its growth biology works, makes cultivating them far less mysterious and much easier to get right.

What Is a Mushroom? The Biology Behind the Growth

Mushrooms are not plants. They belong to the kingdom Fungi, a separate category of life from both the plant and animal kingdoms.

Understanding this distinction explains a great deal about how they grow, what they need, and why they behave so differently from vegetables.

The mushroom itself is the fruiting body of the fungus: the reproductive structure that produces and disperses spores, in the same way that an apple is the fruit of an apple tree.

The main body of the fungus is the mycelium, a network of fine thread-like structures called hyphae that spreads through soil, wood, compost, or whatever substrate the fungus is growing in.

The mycelium is what you see as white, cobweb-like threads when you break apart a rotting log or dig into compost that mushrooms are growing through.

This distinction matters for growers because the visible mushroom is just the endpoint of a longer process.

The mycelium must first colonise the growing substrate, accumulate enough energy reserves, and then receive the right environmental triggers (typically a drop in temperature, increase in humidity, or fresh air exchange) to begin producing fruiting bodies.

Understanding this cycle allows you to manage the conditions that drive each stage.

Spores, Hyphae, and Mycelium: The Growth Cycle

Each mushroom produces millions of spores from structures on the underside of the cap. Spores are single-celled reproductive units, either of compatible mating types.

When a spore lands in a suitable environment, it germinates into hyphae.

When hyphae of compatible mating types meet and fuse, they form the dikaryotic mycelium: the fully formed fungal body that is capable of producing fruiting bodies under the right conditions.

This is why home cultivation uses either spore syringes (which require the spores to germinate and mate) or, more reliably, spawn (pre-colonised grain, sawdust, or other substrate inoculated with established mycelium).

Spawn skips the germination and mating stages and produces colonisation much faster, which is why all practical home cultivation uses spawn rather than starting from spores.

How Fast Do Mushrooms Grow?

Mushroom growth speed varies enormously between species, growing conditions, and the stage of development being measured.

It helps to separate the question into two distinct phases: colonisation (mycelium spreading through the substrate) and fruiting (the development of visible mushrooms from pin stage to harvest).

Do Mushrooms Really Grow Overnight?

The appearance of large mushrooms seemingly from nowhere overnight is one of the most common observations in gardens and lawns.

The reality is more interesting than magic: mushrooms develop through several stages, most of which are invisible or very difficult to see at small sizes.

The pin stage mushrooms, tiny white or brown dots just a few millimetres across, are easy to miss against the soil or among grass.

Once conditions are right (typically warm overnight temperatures combined with moisture from rain or dew), these pins expand rapidly.

Cell expansion in fungi is driven by water uptake rather than the cell division that drives growth in plants, which means a mushroom can increase dramatically in size within hours once expansion begins.

The practical result is that a mushroom that was pinhead-sized at dusk can genuinely be 3 to 4 inches (8 to 10 cm) across by morning, particularly in warm humid summer weather.

This is not growth from nothing; it is the final rapid expansion phase of a mushroom that has been developing slowly and inconspicuously for days beforehand.

How Does Rain Affect Mushroom Growth?

Rain does not make mushrooms grow faster in terms of the underlying biological timeline, but it does provide two things mushrooms need simultaneously: moisture and humidity.

The water uptake that drives the rapid expansion phase requires both adequate soil moisture and high ambient humidity to prevent the growing mushroom from drying out before it reaches full size. Rain delivers both at once.

After sustained rain followed by warm temperatures, the conditions are optimal for the expansion phase to proceed without interruption, which is why mushrooms after rain are larger and more numerous than those that develop in drier conditions.

A mushroom growing during dry weather may stall in its development and dry out before reaching full size; the same species after rain expands fully and quickly.

This is also why mushrooms appear across a lawn or garden all at once after rain: the entire network of mycelium in the soil experiences the same moisture trigger simultaneously and initiates fruiting across a wide area at the same time.

The Fastest Growing Fungus in the World

The stinkhorn fungi, particularly Phallus impudicus (common stinkhorn) and the related Dictyophora indusiata (veiled lady), are among the fastest growing organisms on Earth.

Stinkhorns expand at approximately 0.5 cm per minute during their active growth phase, which means the growth is fast enough to see with the naked eye if you watch carefully.

The rapid cell expansion generates enough mechanical force that the tissues stretch and crackle audibly as the fruiting body pushes up through the soil.

The extraordinary smell of stinkhorns, strongly resembling rotting flesh, is not a flaw but a highly effective spore dispersal mechanism.

The spore mass (the gleba) is carried by flies attracted to the smell; the flies collect spores on their feet and body and transport them far from the parent organism.

Dictyophora indusiata is found across tropical regions of Asia and is considered a delicacy in Chinese cuisine, harvested at the egg stage before the smell develops.

Where Can You Grow Mushrooms?

One of the most appealing aspects of mushroom cultivation is the flexibility of growing location.

Unlike most edible crops, mushrooms do not need light to grow (they do not photosynthesize) and thrive in cool, dark, humid conditions that are often available in spaces unsuitable for other growing projects.

What Conditions Do Mushrooms Need to Grow?

Temperature

Most cultivated mushrooms have two temperature preferences: a warmer temperature for colonisation (mycelium spreading through the substrate) and a cooler temperature for fruiting (producing mushrooms).

This temperature drop mimics the natural seasonal shift from summer to autumn and is often the trigger that initiates fruiting.

Humidity

Mushrooms are composed of approximately 90% water. Maintaining high ambient humidity around the fruiting substrate, typically 80 to 95% relative humidity during the fruiting stage, is essential for the mushrooms to expand fully without drying out.

In a dedicated growing space, a small ultrasonic humidifier achieves this easily.

For kitchen counter kit growing, misting the block with a spray bottle twice daily keeps the surface moist enough for the smaller scale involved.

In the UK, where ambient indoor humidity is often already higher than in dry US climates, maintaining adequate fruiting humidity is often easier, particularly in older homes and in autumn and winter.

In centrally heated homes in both countries, humidity drops significantly during the heating season, making supplemental humidification more important.

Fresh Air Exchange

Unlike most organisms, developing mushrooms are sensitive to elevated carbon dioxide levels. As mycelium and fruiting bodies metabolise, they release CO2.

If this accumulates, it triggers the plant to produce long, thin stems with small or misshapen caps as it reaches upward seeking fresh air.

This is the most common cause of odd-looking mushrooms in beginner growing attempts.

The solution is simple: brief fresh air exchange twice daily. For a grow bag or fruiting chamber, opening the bag or container for a few minutes twice a day is sufficient.

This fans out the accumulated CO2 and replaces it with fresh air. Some growers use a gentle fan on a low setting for a few minutes as an alternative.

The distinctive long stems and small caps of commercial enoki mushrooms are deliberately induced by restricting fresh air exchange; for all other cultivated species, good fresh air exchange produces the properly-formed mushrooms you want.

Light

Mushrooms do not photosynthesize and do not need light to grow.

However, light does affect the direction of growth: fruiting bodies grow toward light (phototropism), which is why mushrooms cultivated in a bag or box with a hole in one side all grow toward the opening.

Normal ambient room light is sufficient; direct intense light is not needed and may dry out the surface of the substrate if it generates heat.

How Long Do Mushrooms Live?

A mature mushroom in the wild or in a growing setup has a relatively short lifespan.

Once the cap has opened and the spores begin to drop, the mushroom’s primary function is complete and it begins to deteriorate.

Most species remain in good condition for 3 to 7 days after reaching full maturity before softening and eventually decomposing.

The practical implications for cultivated mushrooms are straightforward: harvest before the cap fully flattens or the edges begin to curl upward.

At that point the mushroom is still at its best for eating. Waiting for full spore release results in a mushroom that has passed its prime and is beginning to decompose.

For home cultivation, checking the grow block twice daily and harvesting promptly as mushrooms reach the right size produces the best quality.

Wild Mushrooms: Safety and Identification

Wild mushrooms that appear in gardens, lawns, and parks range from edible to severely toxic or deadly.

The critical rule, with no exceptions, is never eat a wild mushroom unless it has been positively identified by someone with significant practical experience in mushroom identification, or verified against multiple authoritative field guides with physical specimens in hand.

If you find mushrooms in your garden and have children or pets, the simplest safe approach is to remove them by digging out the fruiting bodies before they are touched.

Wear gloves when handling any unidentified wild mushroom. Note that the mycelium remains in the soil regardless of removing the mushrooms, and new fruiting bodies will appear under the right conditions; regular removal prevents sporulation and gradually reduces the visible population.

Mushrooms appearing in bark mulch are very common because mulch provides ideal mycelium habitat: moist, rich in organic carbon, and protected from drying out.

These are almost always saprophytic fungi breaking down the organic material in the mulch, which is a beneficial process for soil health, but the mushrooms themselves should be treated as unidentified and not consumed unless properly identified.

Getting Started Growing Your Own Mushrooms

Home mushroom cultivation has become significantly more accessible in recent years.

Ready-to-fruit kit blocks, pre-inoculated with oyster or other species, are available from most garden centres in the UK and from specialist suppliers and many garden centres in the US.

These require no specialist knowledge or equipment and produce harvestable mushrooms within 10 to 14 days of starting.

The Simplest Starting Point: Ready-to-Fruit Kits

• What you get: A block of colonised substrate (typically straw, sawdust, or grain) already fully run through with mycelium; it just needs humidity and fresh air to produce mushrooms
• What you need to do: Open the bag or cut an X in the surface; mist with water twice daily; keep at room temperature (65 to 75 degrees F / 18 to 24 degrees C); harvest when caps are fully formed but before edges curl
• What to expect: First pins in 5 to 10 days; harvestable mushrooms 5 to 7 days after pinning; two to four additional flushes over the following 4 to 8 weeks
• In the UK: Available from most large garden centres, specialist mushroom suppliers (Back to the Roots, Hericium kits from Forest Fungi and similar), and online retailers; oyster mushroom kits are the most widely stocked
• In the US: Available from North Spore, Fungi Perfecti, and garden centres; oyster kits are most common; shiitake log kits are also popular

Outdoor Log Cultivation for Long-Term Production

Inoculating freshly cut hardwood logs with shiitake or oyster mushroom dowel spawn is one of the most rewarding long-term cultivation methods.

The process requires more patience (6 to 12 months before the first harvest) but produces mushrooms for 3 to 6 years from a single log with almost no ongoing maintenance.

Use freshly cut oak, beech, or hornbeam logs (4 to 6 inches / 10 to 15 cm in diameter, 3 to 4 feet / 90 to 120 cm long); drill holes in a diamond pattern across the log; hammer in inoculated wooden dowels; seal each hole with wax; stack logs in a shaded, moist position; and wait.

In the UK, this method suits the naturally cool, moist climate very well and log cultivation is increasingly popular among allotment growers.

Frequently Asked Questions

How long does it take to grow mushrooms from scratch?

From purchasing spawn or a kit to first harvest: approximately 2 to 4 weeks for oyster mushrooms using a ready-to-fruit kit or pre-colonised bag.

From inoculating your own substrate with spawn to first harvest: 5 to 8 weeks for oyster, 3 to 5 months for shiitake on sawdust, 6 to 18 months for shiitake on logs.

The timeline depends entirely on the species and method. For the fastest possible results, a ready-to-fruit oyster mushroom kit is the most reliable choice.

Can I grow mushrooms in an apartment?

Yes. Oyster mushroom kits require nothing more than a kitchen counter or spare shelf, room temperature conditions, and twice-daily misting.

They produce no strong smell during growth (the mushrooms themselves smell pleasant, like fresh oyster mushrooms) and generate no mess beyond the occasional water droplet from misting.

Apartment growing is one of the most common mushroom cultivation approaches, and small-scale kit growing is specifically designed for this context.

Why are my mushrooms growing slowly?

The most common causes of slow mushroom growth are temperature too low (below 60 degrees F / 15 degrees C for most species), insufficient humidity (less than 80% around the fruiting surface), high CO2 from inadequate fresh air exchange, or the substrate not being fully colonised before fruiting conditions were applied.

Check temperature first: this is the most common single factor. Then check that the surface of the substrate stays visibly moist after misting.

If both are correct, increase the frequency of fresh air exchange by opening the growing container or bag twice daily for a few minutes.

Are the mushrooms growing in my garden safe to eat?

Not unless you can positively identify them. Wild mushrooms in gardens include species ranging from completely harmless to fatally toxic, and appearance alone is not a reliable guide.

Some deadly species closely resemble common edible ones.

Unless you have specific training and experience in mushroom identification, or have had the specific mushrooms confirmed by an expert, do not eat them.

If you want to eat fresh mushrooms, cultivate them yourself from verified spawn or kits, where you know exactly what species you are growing.

Do mushrooms grow back after picking?

Yes. The mycelium in the substrate continues to live after harvesting the fruiting bodies and will produce additional flushes under the right conditions.

Most cultivated species produce two to five flushes from a single substrate block before the available nutrients are exhausted.

To encourage subsequent flushes, remove all stumps from the previous harvest completely (any remaining stump tissue can become a contamination point), soak the block in cold water for 2 to 4 hours, then return it to fruiting conditions. The next flush typically appears 7 to 14 days later.

Final Thoughts

Mushroom cultivation is one of the most accessible and rapidly rewarding food-growing projects available to anyone with a small indoor space.

The biology is different from plant growing in ways that make it fascinating: you are working with a living organism that processes its environment, triggers growth through environmental cues, and produces food through breakdown of organic material rather than photosynthesis.

Once you understand the basic requirements of temperature, humidity, and fresh air exchange, the process becomes highly predictable.

For anyone curious enough to try, a simple oyster mushroom kit is the ideal starting point.

Within two weeks you will have a clear practical understanding of how mushrooms grow, what they need, and how satisfying it is to harvest and eat something you have cultivated yourself.

From that foundation, expanding into shiitake logs, more exotic species, or larger indoor setups is a natural and very enjoyable next step.