Why Microgreens Mold and How to Prevent It

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Microgreens have gained popularity in the past couple of years with restaurants and local growers. These small greens are great for garnishes to dishes because of their looks and tastes. Microgreens are harvested seedlings from popular vegetables. However, there are issues with growing microgreens that could ruin the crop. 

One of the most frequent concerns microgreens gardeners raise is why plants mold. The reason is that its often difficult for beginners to know the difference between mold and root hair. You need to understand the difference, and when it is mold and how to act.

So, why microgreens mold and how can you prevent it. There are several reasons for why microgreens mold such as: 

  • Environmental: soggy, humidity
  • Airflow and Lighting
  • Growing devices
  • Seed Issues

There are ways to prevent the growth of mold in the microgreen plants such as:

  • Sanitizing the seed
  • Preventing overseeding
  • Using good quality
  • Control the environment

Growing microgreens is a great side business for some, while others it is a good hobby to start. No matter the reason for growing the microgreens, it is helpful for the grower to understand the process of mold growth and how to prevent it. 

Why Microgreens Mold

Microgreens are vegetable greens that are harvested just after the cotyledon leaves have developed and true leaves have emerged. They are visually pleasing and have good nutritional value. The microgreens are essentially seedlings of edible vegetables and herbs. If done accurately, they will grow to become healthy and nutritious. 

RELATED: The 14 Most Nutritious Microgreens to Grow and Eat

To grow microgreens are easy, but one of the more common problems faced by growers is the invasion of mold. The reason why microgreens get sick and fall over is that the environment they grow in may be too damp or there is not enough light. Other factors may the temperature or even lack of airflow. Let us go deeper into the reasons your microgreens can mold and what you can do about it. 

Mold Types

First, you need to be able to differentiate mold from the root hair. Mold is not root hair that grows on the microgreen roots (make sure to know the difference). Microgreen root hair is white and fuzzy. Mold is a fungus that comes in various forms. Mold on microgreens presents itself as spider-web like material that is white or yellow. There is another mold that can present in a blue/grey fashion with round particles.  

Mold is slimy to touch and does have a musty smell. The mold will be located on the microgreens, soil around the microgreens, and sometimes below the soil level on the roots. 

Mold will kill or stunt the growth of the microgreens. However, you can fix it. If you find the mold fast enough, you can take the microgreens out of the contaminated soil and fix the issues that we will be discussing below. 

Problems that Cause Mold

Just like with any plant process, you should be aware of how things could affect the growing process. There are a couple of different ways that mold can affect the microgreens process.

Soggy Environment and Room Humidity

When it comes to growing microgreens, there should be a good environment for growth to happen. When there are problems with the environment, then you will most likely have problems with the production of your microgreens. 

When microgreens are grown in a soggy environment, then the microgreens have a high chance of mold growth. Mold likes to grow in warm and wet places, which would make your microgreens a huge target. To stop the soggy environment from happening, you should have moisture control measures in place, which we will be discussing in the prevention of mold.

Room humidity plays a big part in the problem of mold growth. Again, mold likes to grow in warm and humid places. If your place has a high humidity (more than 50-60%), you are are at high risk to see mold start to grow on your microgreens. 

Light and Airflow

Microgreens like most plants need light. There is always a balancing act when it comes to how much light to give a plant. Sometimes when the plant has too much light, it will be overwhelmed and die. If the plant is missing enough light, the plant could not produce normally due to nutrients and nourishment being lost. 

Microgreens desire the right amount of light, whether from the sun or artificial lighting. When there is a lack of that balance, the microgreens could either stunt production or start to grow the mold that is listed above. 

Airflow, rather a lack of, is another issue that microgreens could experience when in the growing process. Microgreens need enough airflow in the soil and environment to allow for the plant to be successful. If the airflow is poor in the environment and soil, mold will most likely start to grow. Airflow should also be combined with the right type of air. Microgreens need air that is not humid to avoid mold.

Environment: Grow Areas

Microgreens are pretty easy to grow as long as you have the right grow areas to put them in. The environment for the microgreens is important to avoid stunting growth, killing, or mold in the microgreens.

Soil issues will be a problem for mold growth for microgreens. If the microgreens are in soil that does not have the right nutrients, lack of airflow, and lack of drainage, the microgreens will mold. The soil needs to be consistent for the microgreens to ensure that they will grow successfully. 

Grow devices or planters should be designed to allow the microgreens to grow upwards and allow for room for the plants. If the microgreens are grown in a planter that does not have holes on the bottom, there will be mold issues due to drainage issues. If the planter is not big enough, there will be seedling overcrowding, which will cause mold issues. 

Seed Issues

Microgreen seeds are easy to find now that microgreens have become so popular in the past couple of years. However, you want to make sure that if you are getting microgreen seeds, you are educated on what types, where to buy, and how to grow.

When seeds are bought from a non-reputable seller, there could be an increased chance of mold growth. Seeds need to be good quality from a good seller to be more successful. Seeds also need to be handled (before planting) with care because there could be an increased mold growth if the seeds were improperly cared for. 

Overpopulation of seeds in your planter is another way that may cause mold will grow. If the seed roots do not have enough room in the planter, there will be overpopulation. That means there is not enough room for adequate airflow and drainage in the soil. Mold will grow in this case. 

Prevention of Mold

There are ways to prevent the growth of mold in the microgreen growing process. Most of these techniques were learned the hard way, but now there is knowledge of how to make sure mold doesn’t destroy the microgreen crop. 

Sanitize the Seed

Seed issues are unfortunate when trying to grow the microgreen crop. If you are buying your seeds from a reputable supplier, you will not have to make this step.

However, seed issues account for some of the reasons that either growth production is stopped, ruined by mold, or never started. There are ways that microgreen farmers can stop the problems before it even starts, though. 

Sanitizing the seed will help the microgreen growing process. To sanitize the seed, there needs to be a chemical that is introduced. That chemical is hydrogen peroxide. This chemical will strip any bacteria from the seed to ensure that it does not come with many complications.  

First, get a bowl of water and put just a small amount of hydrogen peroxide into the water solution. For every 1 liter of water you can add 200ml of food grade 3% hydrogen peroxide. Next, put the seeds into the bowl and soak for a few hours. Once the soaking process is complete, you can lay the seeds out on a paper towel to dry. 

This process will also reduce the germination time that it takes the seeds to sprout.

Prevent Overseeding

Microgreen seeds are quite small. They are the seedlings of vegetables and herbs that we use in our most common dishes. However, these seeds will grow into seedlings that need room for growth. 

Overseeding the microgreens will cause mold, but there is an easy enough solution: give them room. Microgreen seeds should be placed far enough away to allow the roots enough space to “root down.” Do not place seeds right next to each other but rather spread them out. If you have trouble getting it right, then try this microgreen seeding density calculator. The calculator can help you to figure out how much space to leave based on the container they are using and the type of plant they want to grow. 

Quality of Seeds

Microgreen seeds are found in most places that sell plant seeds now due to their popularity and good nutritional values. Just like with buying any product, the buyer should do their research on the seller and the quality of the product. The microgreen seeds should be of good quality to ensure good production and less chance of molding.

To get the right quality of seeds, you should identify what type of microgreens you are going to be growing. After you have made your choice, research on good quality seeds should be done to ensure knowledge of what the seed should look like, where to buy it and how the growth process should be done.

Other things that can be done to get good quality seeds would be looking at reviews from other buyers, asking on forums for information, looking into the seller’s business, and asking questions to the seller. There are tons of resources to find the right quality of seeds for microgreens. 

Environmental Prevention

The most important part of prevention for mold growth on microgreens is environmental control. Making sure that microgreens have the right environment will not only help with the production value but also prevent the growth of mold.

Moisture Control

To control the environment that the microgreens are being produced in, there should be control in how much moisture the microgreens are exposed to. Moisture, like with warm/humidity is a major problem for mold growth on the microgreens. There are a couple of ways that moisture prevention can be applied.  

Get trays, planters, or containers for the microgreens that do allow for drainage. This will eliminate the moisture issue within the soil. Most of these containers will have holes on the bottom, which will allow for the water that was not captured by the plants to drain out. 

The soil that you use with microgreens should be set up to help control moisture. Use soilles medium like coconut coir, or get soil that has nutrients in it, such as nitrogen, phosphorus, and potassium. Good soil will need to be able to retain some of the water, so it should have perlite and vermiculite in it to add a “sponge-like” element. Also, adding peat moss or coconut coir will help improve the airflow within the soil.

Humidity Control

Microgreen seedlings will need to be in the right type of environment to grow successfully. Humidity will cause issues of mold growth as well as stunting the growth of the microgreens. Mold likes to grow in warm and wet places, so allowing microgreens to be in a humid area is not advisable.

To control humidity, you should know how much humidity is in the area that you are using. You can measure this by having a thermometer that also reads humidity in the room. These are affordable and easy to buy at your local stores. The thermometer is called a hygrometer. 

Once you know the humidity, the next step is to control it. If the humidity is above 60%, the environment will allow for mold production. Buying and using a dehumidifier will work if the humidity is above 60%. The environment would be best suited around 50-60% humidity. If the humidity of the environment is below 50%, you could use a humidifier. Using a humidifier should be monitored to avoid over-moisturizing the environment.


Growing microgreens needs the right lighting in the environment to control the type of growth the microgreens have. Microgreens do well under most circumstances, but there is some control needed if to avoid mold growth.

The first light that can be used for preventing mold is sunlight. This is the most cost-efficient way to grow microgreens, but the hardest the control for mold growth. Depending on where the microgreens are being grown, the sunlight can be inconsistent. You should consider that you’ll need a minimum of 6-8 hours of sunlight.

If you can’t provide enough natural sunlight, an alternative light that can be used for preventing mold is LED Grow lighting. This type of lighting is a little more expensive but more easily controlled. It is consistent lighting for the microgreens and allows for more consistency within the growing process. You can schedule to turn on and off the grow light (a good reference is to allow for 12-15 hours of light on).


Airflow is another way to prevent mold from growing on the microgreens. Airflow is important in the environment for the microgreens in the quality of air as well as airflow in the soil.

You want to make sure that there is enough air for the microgreens to “breath”. Also, the quality of air should be controlled so that no toxins or chemicals are being exposed to the microgreens. Allowing for fresh air is best for the growth of the microgreen.

Airflow in the soil is also important to cut down on the chances of mold growth. Allowing for the soil to have the right nutrients, prevent overseeding, and using the right container for the microgreens will ensure that the right airflow is available. 


Growing microgreens is easy and rewarding when you finally can harvest those nutritious and healthy greens. However, when you have to deal with mold during the growing process it can cause you to lose your crops. As you are now aware, there are many ways to prevent this from happening. So there is no need to panic if you find that your trays are starting to grow some mold. Just try the tips we have shared and you should be well equipped to have your microgreens turning out just fine.

The sooner you can detect any mold the better of you are. You want to avoid having the mold grow so that you are unable to remove it. Then you will have to throw away the batch and start over. 

Microgreens Corner
Microgreens Corner
We are Janette & Jesper, and we love microgreens.


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