Pinning

After twenty years of running a mycology supply business and helping thousands of cultivators troubleshoot their grows, I can tell you that understanding pins is absolutely fundamental to successful mushroom cultivation. These tiny structures represent one of the most exciting yet frustrating stages in the entire growing process, and frankly, they're where most beginners either celebrate their first success or wonder what went wrong.

What are pins?

Pins are tiny, initial structures that form when mycelium transitions from vegetative growth to reproductive growth, eventually developing into mature fruiting bodies or mushrooms. Think of them as baby mushrooms in their earliest recognizable form, though they're incredibly delicate and can disappear as quickly as they appeared if conditions aren't just right.

Understanding Pins vs. Primordia: The Technical Distinction

Perhaps you've heard the terms "pins" and "primordia" used interchangeably in mycology circles. While they're closely related, there's actually a subtle but important difference that becomes critical when you're troubleshooting problems or timing your environmental adjustments.

Primordia represent a slightly earlier stage in the mushroom fruiting process - the absolute first stage where hyphae begin to change and form structures that no longer look like regular mycelium. These appear as little balls on your substrate. I often describe them to customers as looking like tiny white pearls scattered across the surface.

Pins come next. They're usually more elongated and no longer ball-shaped, and they start to develop what will become the cap, although this can be barely noticeable in some mushroom species. In my experience, pins are when you can start to see the basic mushroom architecture taking shape, even if it's just a pinhead-sized bump with a slightly wider top.

The progression from hyphal knots to primordia to pins typically happens over 2-4 days, though I've seen it occur faster with oysters and slower with shiitakes. Sometimes the stages blur together so quickly that you miss the distinction entirely, which is perfectly normal.

Visual Identification: What Pins Actually Look Like

Pins appear as tiny, white or colored bumps on the surface of the mycelium or substrate, gradually taking on the shape of the mushroom species being cultivated. But let me give you the practical details that help with real-world identification.

Fresh pins typically range from 1-3mm in height and look like tiny white dots or small bumps emerging from the substrate surface. With oyster mushrooms, they often appear as clusters of small white points that seem to emerge overnight. Shiitake pins tend to be more brownish and dome-shaped, while Psilocybe species show characteristic elongated pins with slightly enlarged tops.

The key identifying feature that distinguishes pins from contamination is their organized, purposeful appearance. Contamination usually looks chaotic or fuzzy, while pins have a clean, structured look even at their tiny size. I always tell beginners to use a magnifying glass during this stage; it saves so much confusion and unnecessary panic.

Timing: When Pins Appear in Your Growing Process

Depending on the mushroom species you're growing, it can take 3 to 14 days from when you put your mushrooms in fruiting conditions for visible mushroom pins to form. However, timing varies dramatically based on species, substrate preparation, and environmental management.

From my supply business records, oyster mushrooms typically begin pinning within 3-7 days of initiating fruiting conditions. They're remarkably fast and forgiving, which is why I recommend them for first-time growers. Shiitakes usually take 7-14 days but require that cold shock treatment first. Lion's mane often pins within 5-8 days but can be sensitive to humidity fluctuations during this period.

Critical timing considerations: You absolutely must wait for full colonization before triggering fruiting conditions. Visual confirmation is the best way to tell when your substrate is ready for fruiting conditions, and several factors including temperature variations and spawn rate can influence colonization timing. Rushing this stage is probably the most common mistake I see, and it leads to poor pin sets or contamination.

Environmental Triggers: What Actually Causes Pin Formation

Pin formation isn't random; it's a coordinated response to specific environmental changes that signal to the mycelium that conditions are right for reproduction. Understanding these triggers gives you powerful control over your grows.

Fresh Air Exchange (FAE): Increasing fresh air exchange promotes pinning by reducing carbon dioxide levels around the substrate, simulating natural conditions mushrooms encounter when growing in the wild. Most cultivators aim for CO2 levels around 600-800 ppm for normal pinning, compared to the 1000+ ppm that mycelium prefers during colonization.

Light exposure: Exposure to indirect light or specific light wavelengths can trigger pinning in many mushroom species, acting as a signal that conditions are favorable for fruiting. I've found that blue spectrum light (5000-6500K) at low to moderate intensity (500-1000 lux) works best, typically on a 12-hour cycle.

Temperature changes: Many species require temperature drops to initiate pinning. Shiitakes particularly benefit from a 10-15°F temperature drop for 24-48 hours, while oysters can pin at stable temperatures if other conditions are met.

Humidity management: Maintaining relative humidity of 90-95% during the pinning stage is essential, as lower humidity can cause pins to dry out and abort, while higher humidity can lead to mold and bacterial contamination.

Encouraging Pin Formation: Practical Techniques

After years of troubleshooting grows that "just won't pin," I've developed a systematic approach that works reliably across most species. The key is understanding that pinning is a stress response; you're essentially convincing the mycelium that its survival depends on reproduction.

The Standard Pinning Protocol:

1. Initiate fresh air exchange: Aim for 3-5 air exchanges per hour to maintain ideal CO2 concentration. I use small computer fans on timers for consistent results.

2. Introduce light gradually: Start with 6 hours of indirect light daily, then increase to 12 hours once pins appear. Avoid direct sunlight, which can dry out pins quickly.

3. Maintain surface moisture: The substrate surface should glisten but never have standing water. I mist the walls of growing chambers rather than directly spraying the substrate.

4. Monitor temperature: Most species pin best at 65-75°F, which is usually cooler than their optimal colonization temperature.

For stubborn substrates that won't pin, sometimes a gentle "shock" helps. Cold shocking involves refrigerating the colonized substrate for 12-24 hours, then returning it to normal growing conditions. Temperature shock is a method used for pinhead initiation and increasing yield, though it's somewhat controversial among growers.

Environmental Requirements: The Critical Parameters

Successful pinning requires precise environmental control, and small deviations can mean the difference between abundant flushes and complete failure. Let me share the specific parameters I've found most reliable.

Humidity Control: Aim for relative humidity of 90-95% during the pinning stage. I use digital hygrometers in every growing environment because analog gauges are notoriously inaccurate. Too low and pins desiccate; too high and you get bacterial problems or overlay formation.

Air Exchange Management: If CO2 levels are above 1000-1200 ppm, pin set can be adversely affected. Fresh air exchange serves multiple purposes: it removes excess CO2, provides oxygen, and creates the evaporation that signals fruiting time. I've found that passive air exchange through holes with polyfill works better than aggressive fanning for most species.

Temperature Precision: Optimum air temperature for most species during fruiting is 65-75°F, though species-specific requirements vary. Consistent temperature matters more than perfect temperature; fluctuations stress pins and cause abortions.

Lighting Specifications: Most cultivated mushroom species require at least some exposure to light to initiate proper pin formation. Natural daylight through a window works perfectly, or you can use standard fluorescent bulbs. LED grow lights designed for plants are usually too intense and can actually inhibit pinning.

Development Timeline: From Pins to Harvest

Once pins have formed, the duration from pinning to fruiting typically ranges from 5 to 12 days, depending on the mushroom species and growing conditions. But there's considerable variation, and understanding normal development helps you distinguish between healthy growth and potential problems.

Days 1-3 post-pinning: Pins elongate and develop recognizable caps. This is the most critical period for maintaining environmental stability. Any major changes in humidity, temperature, or air flow during these first days often causes pin abortion.

Days 4-7: Rapid expansion phase. Pins develop quickly, elongating and expanding into recognizable mushroom caps and stems within a few days. During this phase, mushrooms can double in size daily under optimal conditions.

Days 8-12: Final maturation and spore development. Caps fully expand and spores begin forming. Harvest timing can be estimated from pin appearance, as mushrooms typically reach maturity within several days to a week after pinning begins.

Species-specific timing varies significantly. Oysters are remarkably fast, often ready for harvest 5-7 days after pinning. Shiitakes take longer, usually 8-12 days. Lion's mane can be unpredictable, sometimes taking 14+ days to fully develop.

Pin Abortion: Understanding the Problem

Aborts are small pinning mushrooms that cease to grow and never reach full maturity, with caps typically turning black or dark blue. Unfortunately, pin abortion is extremely common and frustrating, but it's also largely preventable once you understand the causes.

Primary causes of pin abortion:

Environmental stress: Any deviation from ideal temperature range (68-77°F), humidity levels, or CO2 concentration can induce stress, leading to stunted growth observed in aborts. Even brief temperature spikes or humidity drops can trigger abortion.

Resource competition: If substrate produces too many fruits, the water-holding part of the substrate doesn't have enough moisture to support all the fruits (fruits are about 90% water), so pins start aborting. This is particularly common with overly-rich substrates or heavy spawn rates.

Inadequate fresh air exchange: High CO2 levels are a major cause of pin abortion. Poor air circulation also prevents proper evaporation, which is essential for healthy development.

Direct water damage: Direct hard misting will cause fragile primordia to abort. Too much water/moisture will cause aborts - you aren't watering them like a plant, just replacing lost moisture.

Contamination stress: Introduction of pathogens or competing fungi can be detrimental, resulting in aborted growth. Contamination doesn't always present obvious visual signs initially.

Preventing Pin Abortion: Proven Strategies

After dealing with countless frustrated customers whose pins keep aborting, I've developed a systematic approach to prevention that addresses the most common failure points.

Environmental stability: The key insight is that pins are incredibly sensitive to change. Once pinning begins, maintain rock-steady conditions. Small amounts of aborts (under 20%) throughout the mushroom cake is absolutely normal, but more than 20% of aborted mushrooms indicates sudden changes in fruiting conditions or poor environmental conditions overall.

Proper misting technique: Misting doesn't cause aborts if you provide adequate fresh air exchange for water evaporation. Mist chamber walls and let humidity levels build naturally rather than directly spraying substrate.

Air exchange management: During the first four days after pinning, air exchange and high humidity are extremely helpful to create a good pin set. I recommend increasing air exchange immediately after pinning becomes visible.

Resource management: For substrates with extremely heavy pin sets, selective thinning helps. If there's an excessive amount of pins that create little mushrooms, some pins can be knocked off to encourage fewer but larger mushrooms. This feels counterintuitive but often saves the flush.

Managing Pin Density: Quality vs. Quantity

Too many fruiting bodies causes nervousness among pickers and a sharp decline in quality. Professional growers have developed sophisticated techniques for controlling pin density that home cultivators can adapt.

Substrate manipulation: Heavy and damp casing reduces mycelium before shock and consequently produces fewer pins. Thicker casing layers also limit pin formation, giving you larger individual mushrooms.

Environmental control: The more gently the shock parameters change during pinning initiation, the fewer mushrooms form. Gradual transitions to fruiting conditions result in fewer but larger pins.

Selective removal: If pin density becomes excessive, early removal helps redistribute resources. The denser the pin set, the earlier you need to start separation and the smaller the fruiting bodies to remove. Remove pins when they're 2-3cm tall for best results.

Harvesting and Using Aborted Pins

Aborted mushrooms are safe for consumption and often more potent than full-grown mushrooms, making them valuable rather than waste products. Remove aborts as soon as possible to prevent potential contamination and allow remaining mushrooms to access more resources.

Identification: The distinctive feature of mushroom aborts are totally black caps or dark-blue caps, with growth that stops completely for 2-4 days. Don't confuse small healthy pins with aborts; aborts have distinctly darkened caps and won't continue growing.

Harvesting timing: The best thing to do when you see mushrooms stopped growing for 4-5 days is to harvest them from the kit. Leaving aborts too long can create conditions for secondary contamination.

Processing and storage: Aborted mushrooms can be dried and stored with other harvested mushrooms. They dry quickly due to their small size and store well for months when properly dehydrated.

Species-Specific Pin Requirements

Different mushroom species have varying pinning requirements and preferences. Understanding these differences is crucial for successful cultivation across multiple species.

Oyster Mushrooms: Prefer higher humidity and more frequent air exchanges. Generally, within 7 days of opening your colonized oyster mushroom kit and providing optimal conditions, you should see oyster mushroom pins forming. They're remarkably forgiving and pin reliably under a wide range of conditions.

Shiitake Mushrooms: Require a drop in temperature to initiate pinning. Cold shocking at 45-50°F for 12-24 hours dramatically improves pin formation. Much more tolerant to high CO2 levels and low light than oyster mushrooms.

Lion's Mane: Extremely sensitive to humidity fluctuations during pinning. Requires consistent 85-90% humidity and gentle air movement. Direct air flow causes pin abortion more readily than with other species.

Psilocybe species: Optimum air temperature during fruiting is 70-74°F. Particularly sensitive to over-misting and require excellent air exchange once pinning begins.

Troubleshooting Common Pin Problems

Problem: No pins appearing after 14+ days in fruiting conditions

• Check colonization completeness; uncolonized areas won't pin reliably
• Verify CO2 levels are dropping with fresh air exchange
• Ensure adequate but not excessive humidity
• Try cold shocking for temperature-sensitive species

Problem: Pins form but remain tiny and don't develop

• Usually indicates insufficient fresh air exchange
• Long stems, underdeveloped caps, and other deformities can result from inadequate lighting, too much moisture, or poor airflow
• Increase air circulation and reduce misting frequency

Problem: Uneven pin distribution across substrate

• Often indicates inconsistent moisture or air flow
• Check for dead zones in your growing environment
• Ensure substrate preparation was uniform

Problem: Pins appear healthy initially but abort within 2-3 days

• Lack of resources is a big cause - if there's too many pins, you can't get mushrooms
• Environmental fluctuations during critical early development
• Consider selective thinning for heavy pin sets

Frankly, pin management separates successful cultivators from frustrated beginners. Observing the pinning response allows cultivators to refine their environmental controls, optimizing conditions to maximize yield and mushroom quality. The investment in understanding this critical stage pays dividends in every subsequent flush, and the principles transfer across virtually all cultivated species.

Most importantly, patience during the pinning stage cannot be overstated. The easiest solution to mushrooms that are slow to produce is patience. I've seen countless growers panic and make environmental changes during pinning that ultimately harm their yields. Trust the process, maintain stable conditions, and let the mycelium do what it's evolved to do over millions of years.