Mold on microgreens: why does it happen and what to do?

When growing microgreens, many people face such a problem as mold. More about why mold on microgreens appears, and how to prevent mold, you may read below.

The appearance of mold on microgreens

Quite often, users confuse mold on microgreens with root hairs. If you are a beginner, it is quite easy to get confused.

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However, several methods will help you find the differences. The microgreens business is popular, so you need to know all the subtleties.

The root hairs are very thin and resemble eyelashes. Root hairs and fuzzy hairs growing form at the roots and make the new seedling bigger.

The root hairs help improve nutrient absorption. Root hairs are practically odorless and form around the roots.

Visually, the root hairs resemble fluffy cotton wool. Root hairs can be seen when microgreens begin to germinate. However, root hairs may appear even around adult bushes.

Determination of mold on microgreens

It is extremely important to correctly determine that mold on microgreens is precisely a sign of a problem.

After all, beginners frequently confuse it, as already mentioned, with root hairs. Mold can take the form of threads that resemble cobwebs. Mold can actively infect the roots, under favorable conditions for it.

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Often, mold on microgreens develops if there is no good drainage, no air circulation, and there is not enough light. There are several signs of mold on microgreens that helps separate the mold from the root hairs.

Among which:

  • an unpleasant odor;
  • the white web appears above the soggy soil surface, and covers the greenery;
  • slimy texture;
  • the appearance of black, purple, and blue spots on microgreens.

Moisture in microgreens

It is not uncommon for people to notice microgreens trays sweating due to mold.

It is caused by pathogens that destroy seedlings at the roots and provoke their death. You risk losing not only one bush but the entire crop.

Pathogens thrive because of a favorable environment.

This is typically caused by not getting enough air in. In this case, fungi begin to develop and multiply, moving between plants.


The defeat will wait not only for the root hairs but also for the stem.

Mold on microgreens will soak up all the nutrients, causing the moldy plant to drop off at the base. Root hairs may turn brown and have a slimy texture.

During the fall of plants, the problem with the lack of air increases. Therefore, pathogens can take over the entire container or stagnant air area.

Causes of unpleasant odor in microgreens

Often people notice that microgreens give off an unpleasant odor.

This suggests that mold on microgreens has begun to develop actively.

Under normal conditions, microgreens have an earthy flavor similar to broccoli or onions.

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If you notice the aroma of rot and swamp, then you should carefully examine everything. An unpleasant smell appears due to the humidity of the tray.

These are ideal conditions for mold to grow. Therefore, such microgreens should be thrown away. It cannot be used.

Mold spots on microgreens

Frequently, the mold affects the surface of the seeds.

You can see signs of mold on the stems and leaf plates. Beginners tend to confuse root hairs with mold.

However, they are present in the root only.

The principle of the microgreen rinse test

The use of a special test helps beginners to determine if there is mold on microgreens. This helps to understand if you are dealing with mold or root hair.

You need to follow a few simple steps.

First, spray the microgreens with water using a spray bottle.

If after spraying, the white fibers do not disappear, then you are faced with mold on microgreens.

If the white hairs are less fluffy after spraying with a spray bottle, then root hairs are present.

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If the root hairs do not change when wet, then you should consider throwing the tray away. You will also need to change the potting mix to avoid problems.

Mold prevention on microgreens

There are a few tips to help prevent mold on your microgreens:

  1. Microgreens should be planted in containers with drainage holes.
  2. The growing medium must be clean.
  3. Constantly monitor how wet the growing medium is.
  4. Allow the air in microgreens to circulate properly using fans.
  5. Light up your microgreens every day. The light must be about 6-10 hours a day.
  6. Seeds that cause you doubts are best soaked and disinfected. To do this, use hydrogen peroxide.
  7. Don’t place microgreen seeds too tightly.
  8. Disinfect containers before growing microgreens.
  9. You should also disinfect pallets using food-grade hydrogen peroxide.
  10. Water your microgreens using the bottom watering.

Causes of mold form on microgreens

Reproduction of fungi and mold is carried out if favorable conditions are created.

Excess moisture

For mold to grow microgreens, a sufficient amount of water is required. Therefore, plants should not be watered abundantly.

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Given that microgreens have a shallow root system, watering should be done every day. The soil should be lightly watered, not flooded.

You can check the quality of watering with your fingers.

Apply some pressure to the growing medium. The soil should be loose, not muddy.

If you prefer to use hydroponics to grow microgreens, then the pads should be kept moist during germination.

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Once the microgreens grow up, you also need to deal with hydration. If it starts to dry out, then water has to be poured into the bottom of the container.

The abundance of moisture and poor drainage cause microgreens mold to grow. Therefore, if your area has high humidity levels, you additionally need a dehumidifier.

It must be kept on so that the humidity indicators are 50-60%.

If you are growing microgreens outdoors, then planting should not be very dense. This prevents the development of mold on microgreens.

Poor air circulation

It is not uncommon for mold to develop on microgreens if it is poor air circulation in the trays. If you notice traces of mold in the containers, then you need to take them outside. Fans can also be placed nearby. As the airflow increases, the humidity decrease.

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However, fans can be harmful. They can spread mold spores to other containers.

Wrong growing medium

It is important to choose the right growing medium. It provides excellent drainage quality, so the root hairs are aerated. The growing medium should not be reused for the next season. After all, this causes mold to develop on microgreens.

If you decide to reuse the medium, then it needs to be sanitized. Food-grade hydrogen peroxide or a bleach solution is suitable for this.

This prevents problems with other batches of microgreens. Sterilization removes harmful substances that cause mold to develop.

It is appropriate to sterilize the pads for growing microgreens in the oven. You need to understand that the process takes a lot of time and effort.

Therefore, many manufacturers advise throwing away old containers and replacing them with new ones.

Detailed methods for preventing mold on microgreens

If you want to prevent mold on microgreens, there are a few guidelines you have to follow.

Container selection

It is better to use trays with holes in the bottom. This prevents the microgreens from molding.

Thanks to this, the water flows down, preventing mold in the root system from becoming excessively moist, rotting, and moldy microgreens. You can drain the water from the drip tray to reduce the humidity of the environment.

Container cleaning

To prevent mold growth, containers should be cleaned before use. This prevents the new batch from becoming contaminated with germs and bacteria.

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Trays can be sterilized using warm water with a little soap added.

After that, the containers should be sprayed with food hydrogen peroxide, and wait a third of an hour. Next, the container is washed and dried.

Seed disinfection

Quite often, mold spores are found in microgreen seeds. Therefore, you need to disinfect all your equipment.

The mix must consist of a few tablespoons of white vinegar with food hydrogen peroxide in equal proportions. Soak the seeds in the solution and wait 10 minutes.

Grapefruit extract is allowed. Grapefruit extract is believed to have disinfectant properties. You need to prepare the correct solution.

To do this, add a few drops of grapefruit extract to 1 liter of water. Microgreens seeds should also be soaked for 10 minutes.

As you know, it is recommended to soak the seeds before planting. This allows you to remove seeds that do not sprout because they are empty inside. Therefore, you can combine soaking and disinfection.

Frequently, there are opinions that microgreens seeds can be treated not only with hydrogen peroxide but also in distilled white vinegar.


You need to keep them for a quarter of an hour. Fortunately, you can buy vinegar in the nearest store.

If you bought seeds from an unverified manufacturer, it is best to process them with hydrogen peroxide several times.

Application of sterile growth medium

The medium intended for growing microgreens must be sterile. Therefore, it is recommended to use soil that is sold in bags. No need to take it from the yard.

It is important to pay attention to the composition of the mixture for growing microgreens. Choose soil that has peat moss or perlite added.

This provides better air circulation and drainage. Combined with the right containers, this prevents microgreens from molding.

Proper seeding frequency

As already mentioned, overseeding encourage mold growth. In the future, when growing microgreens, air circulation deteriorates. Due to overseeding, microgreens are affected by mold. Especially if the conditions are hot and warm.

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In summer, it is recommended to reduce the planting and seed density. On average, thinning is done by half.

Humidity control

As already mentioned, due to high humidity, mold growth will increase. If your area has high humidity levels, you should install a dehumidifier. Humidity indicators should be at the level of 50-60%. Humidity can be reduced if you increase the airflow.

Mold control

If you notice signs of mold on microgreens, take your time to throw away the plants and containers.

There are several ways to help save the situation and the harvest.

Spraying with a disinfectant solution

Mix some food-grade hydrogen peroxide and grapefruit extract. Pour into a spray bottle and start spraying. This kills the microgreens mold.

You do not need to make the solution strong because there may be burns on the leaves.

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Grapefruit extract contains citric acid. It contributes to the destruction of mold and is a natural disinfectant.

The action of hydrogen peroxide can be seen when oxygen begins to be released. The process allows the surface to be oxidized and decomposed.

Growing microgreens in soil

Microgreens can be grown both in soil and hydroponically. However, most users find that planting in the soil increases the ability to control mold on microgreens. If your area has high humidity levels and mold has started to appear, transplant the microgreens into the soil.

Removal of infected areas

This option is appropriate if a small area of microgreens is affected. You can remove infected stems to prevent the mold from spreading further. The rest of the plants need to be treated with grapefruit extract or hydrogen peroxide.

Fan application

If you use a fan, you can improve air circulation. This destroys mold spores. After just a few days of active use of the fan, you notice that the amount of microgreen mold has been significantly reduced. You can also take the tray outside.


As already mentioned, mold prefers to thrive in moist, warm, and dark environments. Therefore, to combat it, plants should be provided with enough light. If the natural lighting is not enough, you can install LED plant lights.

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First, it improves the growth of microgreens. Secondly, you definitely can promote mold growth.

Can you eat moldy microgreens?

If you notice that the microgreen has been affected by mold, it is not recommended to consume it. Yes, mold has likely developed on the surface, which does not bring anything bad to your health. However, you run the risk of filling your body with harmful bacteria that disrupt the digestive system.

If you notice mold, it’s best to throw away the microgreens right away. Believe me, you will only benefit from this.


Can you eat microgreens with mold?

If mold has formed on microgreens, do not use them. After all, it is a danger to your health. It is best to discard the plants so that the white fuzzy growth does not spread to the remaining crop.

Can you wash mold off microgreens?

It is believed that water helps to remove signs of mold. However, some spores remain, infecting the remaining plants.

Why are my microgreens going mouldy?

Several reasons provoke the formation of mold. This is due to excess moisture, dense planting of microgreens seeds, and insufficient lighting. There is also a high chance of infection if you use untreated seeds.


As you can see, microgreen mold can develop for numerous reasons. Therefore, it is essential to properly care for the plants, and monitor the conditions of humidity, lighting, and temperature around them.

Irene Harper

I am a fan of healthy eating, so I studied a lot of information on how to grow microgreens on my own.

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