Growing your first mushrooms is exciting, but it can also raise a lot of questions.
What should early pins look like? How quickly will the mushrooms grow? When should you harvest them? Is the first crop supposed to be large? What happens after it is picked?
The first crop produced by a mushroom block is called the first flush.
Once fruiting begins, some mushroom species can change dramatically from one day to the next. A cluster that looks tiny in the morning may be noticeably larger by the following day.
This guide explains what to expect during your first mushroom flush, from the earliest signs of pinning through to harvest and preparation for another crop.
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What is a mushroom flush?
A mushroom flush is one crop of mushrooms produced by a colonised block.
The first flush begins when small mushroom pins form and ends when the mature mushrooms are harvested.
After the first harvest, the mycelium may rest before producing another crop.
These later crops are called:
- Second flush
- Third flush
- Additional flushes
The number and size of flushes vary.
They can be affected by:
- Mushroom species
- Genetics
- Temperature
- Humidity
- Fresh-air exchange
- The condition of the block
- How much water remains in the substrate
- Care after harvesting
The first flush is often the most substantial, but this is not guaranteed.
Some blocks produce a modest first crop followed by a strong second flush.
What happens before the first flush?
Before mushrooms can fruit, the mycelium needs to grow through the substrate.
With a complete Mushroom Lab grow kit, the process begins by adding the included liquid culture to the all-in-one grow bag.
The mycelium then colonises the grain and substrate inside the sealed bag.
During colonisation, you may notice:
- White growth spreading from the inoculation points
- Small white patches becoming larger
- Mycelium gradually moving through the grain
- More of the substrate becoming covered
- The bag becoming increasingly firm as colonisation progresses
Do not move into fruiting conditions too early.
The grow bag should reach the correct stage before being opened or prepared for fruiting.
Always follow the species-specific instructions supplied with your kit.
For a broader overview of mushroom-growing times, read our guide explaining how long different mushrooms take to grow.
When is a mushroom block ready to fruit?
A mushroom grow bag is generally ready to begin fruiting once the substrate is sufficiently colonised.
The appearance can vary between species.
Some mushroom mycelium becomes thick and bright white, while other species may produce thinner or less uniform-looking growth.
Do not assume every species should look identical.
Signs of healthy colonisation may include:
- White mycelium distributed through the substrate
- Previously loose substrate becoming more connected
- No obvious patches of green mould
- No strong unpleasant smell
- No large areas of unusual discolouration
The exact fruiting point depends on the species and the instructions supplied with your kit.
Starting too early may reduce performance because the mycelium has not fully established itself throughout the available substrate.
What is mushroom pinning?
Pinning is the beginning of visible mushroom formation.
The first tiny mushrooms are called:
- Pins
- Primordia
- Pinheads
These are the earliest visible structures that develop into mature mushrooms.
Pins can look very different depending on the species.
Oyster mushroom pins
Oyster pins often begin as small groups of tightly packed bumps.
As they develop, tiny caps become visible.
The cluster may appear dense and compact before beginning to expand.
Lion’s Mane pins
Lion’s Mane may begin as small white growths that gradually develop into rounded clusters.
The familiar hanging spines usually become more obvious later.
Speckled Chestnut pins
Speckled Chestnut mushrooms may begin as tightly grouped small brown structures.
The caps become more defined as the cluster matures.
King Oyster and Black Pearl pins
These may develop thicker stems and more individual-looking mushrooms than clustered oyster species.
The shape can vary depending on humidity and fresh-air exchange.
How long does pinning take?
There is no single timeline that applies to every mushroom species.
Pinning can be affected by:
- Mushroom variety
- Fruiting temperature
- Humidity
- Fresh air
- Light
- Condition of the colonised block
- How recently fruiting conditions were introduced
Some oyster mushrooms can respond quickly once suitable fruiting conditions are provided.
Other gourmet species may take longer.
Do not assume a block has failed simply because pins do not appear immediately.
Maintain suitable conditions and avoid repeatedly changing the setup.
What should healthy mushroom pins look like?
Healthy pins are usually:
- Firm
- Well formed
- Appropriate in colour for the species
- Gradually increasing in size
A healthy cluster should continue developing once conditions remain suitable.
Some variation is normal.
Not every pin will necessarily become a mature mushroom.
A block may produce more early pins than it can support through to full maturity.
What are mushroom aborts?
An abort is a young mushroom that begins developing but stops growing.
Aborts may remain small while the surrounding mushrooms continue to expand.
Possible causes include:
- The block directing resources towards stronger mushrooms
- Low humidity
- Environmental changes
- Unsuitable temperature
- Drying
- Stress during early development
A small number of aborted pins does not automatically mean something is wrong.
It is common for a cluster to naturally prioritise some mushrooms over others.
How quickly do mushrooms grow after pinning?
Once pins are established, growth can become surprisingly fast.
Oyster mushrooms in particular can increase noticeably in size each day.
The speed depends on:
- Species
- Temperature
- Humidity
- Fresh-air exchange
- Available moisture
- Size of the developing cluster
This is one of the most enjoyable stages of home mushroom growing.
Check the mushrooms daily because harvest time can approach quickly.
Why do mushrooms sometimes seem to grow overnight?
Mushrooms can expand rapidly because their growth is different from the growth of many plants.
Once the fruit body has formed, cells can expand quickly as water moves through the developing mushroom.
This can make growth appear sudden.
A cluster may look compact one evening and much larger the following morning.
The final stages before harvest can be especially quick in oyster mushrooms.
What conditions does the first flush need?
The main fruiting conditions are:
- Suitable humidity
- Fresh-air exchange
- Indirect light
- An appropriate temperature
The balance between these factors matters.
Too little humidity may dry the developing mushrooms.
Too little fresh air may change their shape.
Strong direct sunlight may increase temperature and reduce humidity.
For more detail, read our complete guide to mushroom fruiting conditions at home.
How much humidity does the first flush need?
Young pins can be sensitive to dry conditions.
Humidity helps prevent them from drying out before they develop.
Possible signs that the growing area is too dry include:
- Pins stopping
- Dry mushroom edges
- Cracking
- Yellowing
- Browning
- Hard or dry areas on Lion’s Mane
The goal is to maintain humidity around the fruiting area without repeatedly soaking the mushrooms.
Follow the misting guidance supplied with your kit.
Should you spray water directly onto the mushrooms?
Avoid assuming that more water always produces better results.
The purpose of misting is usually to support humidity around the growing area.
Repeatedly soaking mature mushrooms can cause water to remain on the fruit bodies.
Depending on the setup, you may be instructed to mist:
- Around the fruiting area
- The inside of a humidity tent
- The walls of the growing enclosure
Use a clean spray bottle and follow the instructions supplied with your kit.
Why is fresh air important during the first flush?
Mushrooms use oxygen and release carbon dioxide.
If the fruiting area is too enclosed, carbon dioxide can build up.
This can affect mushroom shape.
Oyster mushrooms with insufficient fresh-air exchange may produce:
- Long stems
- Small caps
- Thin clusters
- Stretched growth
Lion’s Mane may develop:
- Branching growth
- Coral-like structures
- Shorter or less defined spines
Fresh air is important, but strong direct airflow can dry the mushrooms.
The aim is regular air exchange without placing the cluster directly in front of a powerful fan.
Do mushrooms need light during the first flush?
Mushrooms do not use light in the same way plants do.
However, many species benefit from indirect light during fruiting.
A normal room with soft daylight is often suitable.
Avoid:
- Strong direct sunlight
- Hot windowsills
- Constant intense lighting
The kit does not usually need to sit directly beside a window.
A bright room with indirect light is generally enough.
How can you tell when oyster mushrooms are ready to harvest?
Oyster mushrooms grow in clusters.
They are generally harvested once the caps have expanded but before they become overmature.
Watch the edges of the caps.
As the mushrooms mature, the caps gradually flatten and expand.
Avoid waiting until the cluster becomes very old, dry or heavily curled.
Because oyster mushrooms can develop quickly, check them daily as they approach maturity.
Harvest guidance can vary between oyster species, so follow the instructions supplied with your kit.
When should you harvest Lion’s Mane?
Lion’s Mane changes gradually as it matures.
The hanging spines become longer and more defined.
A healthy mature Lion’s Mane is usually:
- White to cream
- Dense
- Covered in visible hanging spines
Do not wait until the mushroom becomes heavily yellow, brown or dry.
Some slight cream colouring can develop naturally as the mushroom matures.
For more detailed guidance, read our complete Lion’s Mane growing guide.
When should you harvest Speckled Chestnut mushrooms?
Speckled Chestnut mushrooms develop clustered brown caps with distinctive pale markings.
As they mature:
- The stems lengthen
- The caps expand
- The cluster becomes more open
Harvest before the mushrooms become overmature or begin deteriorating.
Their stems are edible, so the full cluster can be used in cooking.
When should you harvest Black Pearl King Oyster mushrooms?
Black Pearl King Oyster mushrooms naturally produce thicker stems than many clustered oyster species.
They are usually harvested once the mushrooms have developed substantial stems and mature caps.
Do not judge them using the appearance of Grey or Blue Oyster mushrooms.
Their natural shape is different.
Give the mushrooms enough room to develop and follow the harvest guidance included with the kit.
How do you harvest a mushroom cluster?
Use clean hands.
Support the mushroom cluster close to the base.
Depending on the species, it may be removed by:
- Gently twisting
- Carefully pulling
- Cutting cleanly near the base
Avoid damaging the surrounding block unnecessarily.
Remove loose mushroom material from the fruiting opening after harvesting.
Do not dig deeply into the substrate.
The block may still have enough energy and moisture to produce another flush.
Should you cut or twist mushrooms when harvesting?
Both methods can work depending on the species and cluster shape.
The most important points are:
- Keep handling clean
- Avoid tearing large sections from the block
- Remove the full mature cluster
- Avoid leaving excessive mushroom material behind
Large oyster clusters are often easy to remove by supporting the base and gently twisting.
A clean knife can also be used where appropriate.
How large should the first flush be?
There is no guaranteed first-flush size.
Harvest size varies because mushroom growing is a biological process.
Results are affected by:
- Species
- Genetics
- Colonisation
- Temperature
- Humidity
- Fresh air
- Moisture content
- Fruiting conditions
Two blocks of the same species may not produce identical harvests.
A smaller first flush does not necessarily mean the block is finished.
Some blocks produce stronger later crops.
Why is my first flush smaller than expected?
Possible reasons include:
- The block was fruited too early
- Humidity was too low
- Temperature was unsuitable
- Fresh-air exchange was limited
- The block lost moisture
- Environmental conditions changed
- The species naturally produces a smaller crop
Avoid judging the entire grow from one cluster.
Continue following the aftercare instructions because the block may produce another flush.
Why are my oyster mushroom stems long?
Long stems with relatively small caps commonly suggest insufficient fresh-air exchange.
The mushrooms are responding to elevated carbon dioxide around the fruiting area.
Increase fresh-air exchange gradually.
Avoid placing the cluster directly in front of a strong fan because this may cause drying.
Why are my mushroom caps dry or cracked?
Dry or cracked caps may be associated with:
- Low humidity
- Central heating
- Direct airflow
- Strong sunlight
- High temperature
- Rapid drying
Check the environment around the grow kit.
Move it away from radiators and direct sunlight.
Maintain humidity according to the kit instructions.
Why are my mushrooms yellow or brown?
Colour changes can have several causes.
Possible reasons include:
- Dry conditions
- Age
- Overmaturity
- Environmental stress
- Direct airflow
- Natural colour change
Lion’s Mane may develop cream or yellow areas as it matures.
Large dry or brown areas may indicate that the environment has become too dry.
Why did some pins stop growing?
Not every pin becomes a mature mushroom.
A cluster may naturally direct resources towards the strongest developing mushrooms.
Environmental conditions may also affect pin development.
Check:
- Humidity
- Temperature
- Fresh-air exchange
- Drying
- Recent changes to the setup
Maintain stable conditions rather than making several adjustments at once.
Why are mushrooms growing in an unusual shape?
Mushroom shape can be influenced by:
- Fresh air
- Humidity
- Temperature
- Light
- Available space
Different species also have very different natural forms.
Unusual growth does not automatically mean contamination.
Compare the growth with the expected appearance of the species.
What should you do after harvesting the first flush?
After harvesting:
- Remove loose mushroom material from the fruiting area.
- Follow the kit’s rehydration or resting instructions.
- Maintain suitable conditions.
- Allow the block time to recover.
- Watch for new pin formation.
The block may not begin another flush immediately.
A rest period is normal.
What is a second flush?
A second flush is the next crop produced after the first harvest.
The mycelium remains active inside the block.
If enough nutrients and moisture remain, it may produce another group of mushrooms.
The second flush may be:
- Smaller
- Similar in size
- Occasionally larger
Results vary.
Later flushes often take longer than the first.
How long does a second flush take?
The time varies depending on:
- Species
- Moisture
- Temperature
- Block condition
- Aftercare
Some blocks begin new growth relatively quickly.
Others require a longer resting period.
Continue following the kit instructions and avoid discarding the block immediately after the first harvest.
Can a mushroom grow kit produce a third flush?
Some mushroom blocks can produce a third or additional flush.
Later crops are often smaller because the block has already used much of its available water and nutrients.
The number of possible harvests differs between species and individual blocks.
Continue caring for the block while it remains healthy and productive.
Is the first flush always the biggest?
No.
The first flush is often substantial, but it is not always the largest.
A block may produce:
- A strong first flush
- A smaller second crop
- A modest first crop followed by a larger second flush
Biological variation is normal.
Judge the grow across the full productive life of the block rather than from one harvest.
Can you eat mushrooms from the first flush?
Yes.
Harvested mushrooms should be cooked and stored appropriately.
Use them while fresh.
Different species have different flavours and textures.
Blue and Grey Oyster mushrooms are versatile.
Lion’s Mane has a tender, fibrous texture.
Black Pearl King Oyster mushrooms are firmer and meatier.
Speckled Chestnut mushrooms have a rich savoury flavour.
How should freshly harvested mushrooms be stored?
For short-term storage:
- Keep the mushrooms refrigerated
- Avoid sealing them while wet
- Use breathable packaging where possible
- Cook them while fresh
Excess moisture can make mushrooms become soft or slimy.
Avoid washing them until you are ready to cook.
Common first-flush mistakes
Fruiting too early
Starting the fruiting stage before the substrate is ready may reduce performance.
Follow the instructions supplied with the kit.
Keeping the grow somewhere too dry
Radiators, direct sunlight and strong airflow can dry developing mushrooms.
Sealing the mushrooms into stale air
Humidity is important, but the fruiting area still needs fresh-air exchange.
Misting too heavily
The goal is suitable humidity, not constantly wet mushrooms.
Moving the kit repeatedly
Choose a suitable location and allow time for the mushrooms to respond.
Waiting too long to harvest
Some mushroom species mature quickly.
Check the cluster regularly once it approaches full size.
Throwing the block away after the first crop
Many healthy blocks can produce another flush.
Follow the aftercare instructions before deciding the block is finished.
A simple first-flush checklist
Before fruiting:
- Allow the bag to reach the correct colonisation stage
- Follow the species-specific instructions
- Prepare a suitable fruiting location
During pinning:
- Maintain humidity
- Provide fresh air
- Keep the kit in indirect light
- Avoid direct heat
During growth:
- Check the mushrooms daily
- Look for signs of drying
- Monitor mushroom shape
- Avoid repeated major changes
At harvest:
- Harvest at the correct stage
- Use clean hands
- Remove the mature cluster carefully
After harvest:
- Clean loose mushroom material from the opening
- Follow the rehydration guidance
- Allow the block to rest
- Watch for another flush
Frequently asked questions
What does first flush mean?
The first flush is the first crop of mushrooms produced by a colonised block.
How long does the first mushroom flush take?
The timeline varies by species and growing conditions.
Some oyster mushrooms develop quickly after pinning, while other gourmet mushrooms take longer.
How quickly do mushrooms grow after pins appear?
Some mushrooms can increase noticeably in size every day.
Oyster mushrooms are particularly fast once active growth begins.
Does every pin become a mushroom?
No.
Some pins stop developing while stronger mushrooms continue growing.
A small number of aborted pins can be normal.
Should I mist the mushrooms directly?
Follow the instructions supplied with your kit.
The goal is usually to maintain humidity without repeatedly soaking the mushrooms.
Why are my oyster mushrooms growing long stems?
Long stems with small caps commonly suggest insufficient fresh-air exchange.
Why is my Lion’s Mane growing like coral?
Branching or coral-like growth may be associated with elevated carbon dioxide and insufficient fresh-air exchange.
How do I know when mushrooms are ready to harvest?
Harvest timing depends on the species.
Oyster caps expand and flatten, while Lion’s Mane develops longer hanging spines.
Follow the harvest guidance supplied with your kit.
Will my mushroom kit grow again?
Many healthy mushroom blocks can produce another flush after harvesting.
Results vary depending on the species and growing conditions.
Is the second flush smaller?
Later flushes are often smaller, but this is not always the case.
Some blocks produce a stronger second crop.
Enjoy the process, not just the final harvest
Your first mushroom flush is one of the most rewarding parts of growing at home.
The changes can happen quickly.
Tiny pins develop into recognisable mushrooms, clusters expand and the block produces a fresh crop that can be harvested and cooked.
Do not worry if every mushroom does not look perfect.
Small differences in shape, size and growth speed are normal.
Focus on providing suitable humidity, fresh air, indirect light and temperature.
Observe how the mushrooms respond and make small adjustments when necessary.
After harvesting, continue caring for the block.
Your first flush may only be the beginning.
Explore more than 20 mushroom grow-kit varieties →
Written by The Mushroom Lab
We develop gourmet mushroom cultures and home-growing kits in Northern Ireland, with practical guidance designed to help new growers understand every stage from inoculation and colonisation through to fruiting, harvest and additional flushes.
