The Role of Light in Mushroom Cultivation

When we think of growing mushrooms, we often imagine dark, damp environments, like caves or dense forests. However, the question of whether mushrooms actually need light to grow is more complex than it seems.

Indeed, although fungi do not carry out 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 growing mushrooms and how to optimize this aspect for successful cultivation. We will also look at the negative effects of a lack of light.

Mushrooms and Photosynthesis

Unlike plants, fungi are heterotrophic organisms: they do not carry out photosynthesis and therefore do not use light as an energy source. Mushrooms 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 fungi, including the regulation of certain aspects of their development, such as fruiting and growth orientation.

The Role of Light in the Life Cycle of Mushrooms

Although fungi do not require 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:

Fruit Set Stimulation

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

This light can be natural or artificial, as long as it is in a suitable spectrum (white light or blue light).

Orientation and Growth Direction

Mushrooms use light to guide 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 the mushrooms Coprinus and Agaricus . This response to light helps the mushrooms find ideal conditions for the dispersal of their spores.

Impact on Mushroom Quality

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

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

Light Needs 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 mycological cultivation:

• Oyster mushrooms (Pleurotus spp.): These mushrooms generally require diffused light to initiate fruiting. An intensity of 500 to 1000 lux for 12 hours per day is often recommended.
• Button mushrooms (Agaricus bisporus): This species grows mainly 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 in the Incubation Phase?

During the incubation phase, light is generally not necessary for the majority of fungal 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 very dim light. This promotes rapid and efficient colonization of the substrate by the mycelium, avoiding any unnecessary energy spent in reaction to light.
• Temperature and Humidity: During incubation, it is essential to maintain temperature and humidity levels appropriate for the species of mushroom 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 shiitake, low light could even have a positive impact on the pop corning and browning phase. That said, for the rest, darkness will be preferable. In fact, it may be beneficial to avoid light to save energy and maintain a more stable environment for the mycelium. 

Transition to Fruition

Once the substrate is completely colonized by mycelium, light becomes a crucial factor in triggering fruiting. At this point, the introduction of adequate light allows the fungi to begin to form fruiting bodies, beginning the next stage of their life cycle.

What Light Should You Use for Growing Mushrooms?

Depending on your fruiting space, you can sometimes make do with a source of natural light, if you have a cellar with a vent 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 right light:

Specter of Light

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

Intensity and Duration

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

Temperature and Humidity

Light can increase the 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 lights are too close to the terrarium or mycelium, it can cause overheating or burning, which can damage your mushrooms or prevent fruiting bodies from forming. Be sure to leave plenty of space and watch carefully for any signs of burning, especially if you are using very powerful grow lights.

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

The Impacts of a Lack of Light on Mushroom Growing

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

Abnormal Growth :

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

Color and Appearance :

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

Development of Primordia

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

Quality and Performance

The overall quality of mushrooms may be compromised, with less than optimal texture and density. Yield may 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, notably fruiting.

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

As a grower, you can adjust the light based on the species you are growing to achieve the best possible results.