The Role of Light in Mushroom Cultivation

When thinking about mushroom cultivation, one often imagines dark and humid environments, such as cellars or dense forests. However, the question of whether fungi really need light to grow is more complex than it seems.

Indeed, although fungi do not perform photosynthesis like plants, light still plays a crucial role in their development and growth.

In this article, we explore in detail the role of light in mushroom cultivation and how to optimize this aspect to succeed in your crops. We will also examine the negative effects of a lack of light.

Fungi and Photosynthesis

Unlike plants, fungi are heterotrophic organisms: they do not perform photosynthesis and therefore do not use light as an energy source. Fungi feed by decomposing organic matter, whether plant, animal, or other. However, this does not mean that light is unimportant to them.

Indeed, light is involved in several vital processes in mushrooms, notably the regulation of certain aspects of their development, such as fruiting and growth orientation.

The Role of Light in the Mushroom Life Cycle

Although mushrooms do not need light to produce energy, light plays an essential role at different stages of their life cycle. Here are the main effects of light on mushrooms:

Fruiting Stimulation

For many mushroom species, light is an important trigger for fruiting (the formation of mushrooms from mycelium). For example, oyster mushrooms (Pleurotus spp.) require light exposure to produce sporophores (fruiting bodies).

This light can be natural or artificial, as long as it falls within an appropriate spectrum (white light or blue light).

Orientation and Growth Direction

Mushrooms use light to orient their growth. In the laboratory, it is common to see sporophores moving toward the light source, a phenomenon known as positive phototropism.

This can be observed, for example, in Coprinus and Agaricus mushrooms. This light response helps mushrooms find ideal conditions for spore dispersal.

Impact on Mushroom Quality

Adequate exposure to light can improve the color, texture, and even nutrient content of certain mushrooms. Mushrooms that grow in total darkness can sometimes be pale or less visually appealing.

On the other hand, controlled light can produce more robust and aesthetically pleasing mushrooms. The quality of the mushroom can thus be optimized through careful light management.

Light Requirements Vary by Species

It is important to note that not all mushrooms have the same light requirements. Here are some examples of specific needs for different common species in mushroom cultivation:

• Oyster Mushrooms (Pleurotus spp.): These mushrooms generally require diffuse light to initiate fruiting. An intensity of 500 to 1000 lux for 12 hours a day is often recommended.
• Button Mushrooms (Agaricus bisporus): This species mainly develops in darkness or under very low light. Intense light can even inhibit fruiting.
• Shiitake (Lentinula edodes): Shiitakes also require moderate light to initiate fruiting, but too intense light can cause burns or defects on the mushroom caps.

Light During Incubation Phase?

During the incubation phase, light is generally not necessary for the majority of mushroom species. This phase, crucial for the initial development of the mycelium, focuses more on creating an optimal environment in terms of temperature and humidity.

Incubation Conditions

• Darkness or Low Light: Most mushrooms prefer to be incubated in darkness or under very low light. This promotes rapid and efficient colonization of the substrate by the mycelium, avoiding any unnecessary energy spent reacting to light.
• Temperature and Humidity: During incubation, it is essential to maintain temperature and humidity levels suitable for the mushroom species being cultivated. These two factors are the most critical at this stage, as they directly influence the speed and success of substrate colonization.

Exceptions

Some species can tolerate low ambient light, but this is generally not necessary. For shiitakes, low light might even have a positive impact on the "pop corning" and "browning" phases. That said, for the rest, darkness will be preferable. In fact, it can be advantageous to avoid light to save energy and maintain a more stable environment for the mycelium. 

Transition to Fruiting

Once the substrate is fully colonized by the mycelium, light becomes a crucial factor to trigger fruiting. At this stage, introducing adequate light allows mushrooms to start forming fruiting bodies, thus initiating the next stage of their life cycle.

What Light to Use for Mushroom Cultivation?

Depending on your fruiting space, you may sometimes be content with a natural light source, if you have a cellar with a small window, for example. But if your growing space is too dark, the use of artificial light will be necessary to have beautiful, good quality fruits.

Here are some tips for choosing the appropriate light:

Light Spectrum

Light in the blue spectrum is generally effective for mushroom fruiting. So you will look for spectra with a minimum of 6000 kelvin, in cool whites. Full-spectrum LED or fluorescent lamps are often used.

Intensity and Duration

A moderate light intensity (500 to 1000 lux) for about 8 to 12 hours a day is sufficient for most mushrooms. A day/night cycle is often simulated to mimic natural conditions.

Temperature and Humidity

Light can increase ambient temperature. It is therefore crucial to monitor environmental conditions, as mushrooms also require specific levels of temperature and humidity for optimal growth.

Beware of Overheating

It is essential to avoid excessive heat. If your lamps are too close to the terrarium or mycelium, this can cause overheating or burns, which can damage your mushrooms or prevent fruiting formation. Make sure to leave enough space and carefully monitor any signs of burning, especially if you use very powerful grow lights.

Example of abnormal growth of grey oyster mushroom caused by a lack of light.

The Impacts of a Lack of Light on Mushroom Cultivation

A lack of light can have several impacts on mushroom development, especially during the fruiting phase. Here are some potential effects:

Abnormal Growth:

Mushrooms may develop longer stems and smaller caps as they try to "stretch" toward a light source.

Color and Appearance:

The color of the mushrooms can be affected. For example, some mushrooms may become paler or have uneven pigmentation.

Primordia Development

The formation of primordia (young mushrooms) can be delayed or inhibited, as light often acts as a trigger for this phase.

Quality and Yield

The overall quality of the mushrooms can be compromised, with less optimal texture and density. Yield can also be reduced if light conditions are not adequate.

Conclusion: Adapting Light to the Needs of Mushrooms

In conclusion, although mushrooms do not need light to feed, light remains a key factor for certain stages of their life cycle, especially fruiting.

Each mushroom species has specific light requirements, and it is important to understand these needs well to optimize the growth and quality of your crop.

As a grower, you can adjust the light according to the species you cultivate to achieve the best possible results.