Proper Microgreens Airflow: Without it, They Wilt and Mold

During the first few months of starting JPure Farms, we spent a lot of time fussing about microgreens airflow.

If you grow microgreens indoors (greenhouse, vertical or container farm, micro-urban farm, basement urban garden, or windowsill), then microgreens airflow and ventilation are essential considerations.

What are the symptoms of poor ventilation when growing microgreens indoors?

Are you just starting out and wanting to know about microgreens airflow and ventilation?

Or do you have a specific problem with your grow room ventilation system?

Efficient microgreens airflow is vital in growing healthy plants. Proper ventilation supports plant transpiration and avoids depleting the grow room CO₂ supply. Ventilation fans maintain adequate room humidity and temperature. And fresh air intake and circulation stop pest, mold, and rot issues.

You may be asking yourself, “why do grow rooms need ventilation?”

Okay, but how do I vent my microgreens grow room?

And what kind of fan do I need to buy?

But just putting a fan in the corner doesn’t give you a sound microgreen ventilation system for your grow room.

I promise you will know how to implement proper microgreens airflow by the time you finish reading this post.

Why Do You Need Proper Microgreens Airflow?

When we started JPure Farms in the summer of 2019, we were in the basement of my partner Stephen’s home.

There was one interior door and one exterior door, and a two-panel window.

We started small, a vertical stand with three rows for our microgreens.

We closed the windows and covered them with black cloth during the first two to three days before germination.

After they germinated, we had a fan in the door to the outside bringing in the fresh air and circulating it during the day.

No problems.

Prevent Pests and Diseases

Until about day four or five.

That’s when we started finding pests like spider mites, white flies, and fungus gnats in the soil.

Even though we had good air circulation during the day, it turned out that we made a few mistakes.

We closed the window and the door in the evening, watered the plants and put them under grow lights.

These pests laid their eggs in the damp topsoil.

And while the daytime fan slowed their reproduction, it wasn’t enough to prevent them from eating out young seedlings.

If we were going to make a business of this, we needed something better or different.

Stop the Wilting With Temperature Control

Well, you can imagine the heat in an underground basement during the summer.

The room was a standard US bedroom, 11 ft x 12 ft (132 square feet).

The good news was the room was air-conditioned.

We did some research, asked around, and found the best microgreen grow rooms maintain a temperature between 75- and 85-degrees Fahrenheit.

All plants love fresh air. Microgreens are no exception.

We added a small oscillating fan from Amazon.

And we started growing again until we hit the next hurdle.

Sure, adequate ventilation helps circulate the air in a way that better maintains cool temperatures.

But we forgot one thing.

There wasn’t an air conditioner return vent in the room.

Exhaust fans, the kind that blows air out of the room, get rid of excess heat in the room, while oscillating fans blow cool, fresh air on the plants.

One of the other problems we recognized was the high-powered grows light also generated heat.

The microgreens started to wilt.

It seems that a difference of just a degree or two radically affected the health of our microgreens.

Time for something different.

This time we went big!

Preventing Mold with Dehumidifying

We learned that even though the room was cool, it was drier than the environment inside the microgreens’ cells.

Plants emit water vapor throughout the day, which increases the humidity.

Moisture was leaving the microgreens cells and moving into the air in the room.

The process, called transpiration, was what was causing the microgreens to dehydrate and wilt.

Not only did we have to control the temperature, but we also had to control the high humidity.

So, we decided to turn close off the air conditioning vent and get a dehumidifier, like this one from Amazon.

And this time we decided to create a “real” microgreens indoor grow room.

We bought some panda plastic film to cover the walls.

We got a 5.5 Mil 10′ x 100′ roll from Amazon.

What we learned was mold is in the air around us.

Mold can remain dormant within an extensive range of temperatures.

It starts growing when it has a food source and air that is moist, warm, and not circulating.

And if not controlled, most temperatures above 70^oF will cause their rapid growth.

Also, because of the water in the room for growing the microgreens, the humidity was closer to 70%.

After germination, it took us weeks to keep the humidity between 50 and 55%.

We lost a lot of crops to mold and some to root rot.

It was a balancing act as the dehumidifier pulled water from the surrounding air and returned it back dry.

Why Do You Need to Ventilate Your Grow Room?

Remember that air circulates more naturally outdoors.

To simulate or replicate that kind of airflow indoors, you need both a fan and an air extractor.

And microgreens love fresh air.

Place Oscillating Fans in the Grow Room

As we learned how to vent our grow room, we better understood that a microgreens ventilation system needed two types of fans.

Extractor fans that expel the hot and humid air
Oscillating fans that swing from side to side

The oscillating fans were easy to place in the room.

You can move them around quickly with electrical extension cords.

This way, you can find the best location in your grow room.

The bigger the room, the more fans you may need.

You want to be careful to avoid pointing the fans directly at the microgreens trays.

What’s called “windburn” can damage your plants, just like any strong outdoor wind can.

If you’re growing your microgreens on the windowsill at average room temperature, you should be okay.

But it doesn’t hurt to have a tiny fan moving the air, especially if you can’t open the window or it how outside.

Oscillating fans circulate and keep the air cool.

But oscillating fans alone won’t make the air in the microgreens grow room fresh.

Use Extractor Fans to Keep the Air Fresh

We eventually had to add an air extractor system in the basement window.

Those fans above your stove and in your bathrooms are extractor fans.

Extractor fan systems push out the old air and bring in the fresh air.

The extractor should be able to do this every three to five minutes.

So, you need to choose the right size fan.

How to Calculate Fan Size

You need some basic arithmetic and multiplication.

CFM stands for cubic feet per minute and measures a fan’s ability to circulate air.

The bigger the room, the higher the CFM rating.

To calculate the CFM of your microgreens grow room:

The dimensions: length x width x height
The exhaust efficiency: the length the air travels from your room to the outside (short 2, medium 3, long 4)

The fan CFM = Volume of room x Exhaust efficiency

Our original microgreens grow room was 11 ft x 12 ft x 9ft = 1188 cu ft

But we had a short window so CFM = 1188 x 2 = 2376.

According to the local hardware store, a fan should have a CFM rating high enough to replace the air in a 6ft x 6ft x 8ft space at a rate of eight times per hour.

Check out this video.

Managing CO2 Levels

When we grow microgreens or any plants indoors, we substitute fans and air conditioners for breezes and evaporation, grow lights for sunshine, and watering systems for rain and dew.

Microgreens need the CO2 that comes naturally with fresh outside air.

They need it throughout the day as part of the nutrient cycle.

They the CO2 and the grow lights for photosynthesis after germination.

If you have a sound ventilation system, one that circulates fresh air from outside and removes the old air from your grow room, you will boost your microgreens yield.

I bet you didn’t know that at night your microgreens reverse photosynthesis.

They take in oxygen and release carbon dioxide.

So, it is imperative that during the “day,” you extract the used air and circulate fresh air.

If your grow room doesn’t have an exhaust fan, add extra circulation fans.

We learned the hard way how important this is to maintain consistent microgreens health.

Other Factors to Consider for Microgreens Air Flow

When your business starts growing, you have to be able to deliver fresh produce consistently.

You may have to consider installing an industrial airflow device that delivers fresh air 24×7.

Using an evaporative cooler in conjunction with an exhaust fan is another way to cool your grow room in hot climates. They are more efficient than air conditioners and use about 10 times less energy.

Grow Rack Fans

Researchers at Brunel University have been experimenting with boos vertical farming yields by more than 20%. They have created a prototype growing system with built-in fans.

Microgreens Ventilated Growing System — Courtesy Brunel University

The Bottom Line

Microgreens ventilation systems control the humidity, temperature, airflow, and carbon dioxide required o grow healthy microgreens.

Good airflow is critical for growing healthy microgreens.
Low airflow leads to mold, pests, and root issues.
If you have a greenhouse or grow room, natural airflow plus fans work best.
Microclimates form around the microgreens trays. Continuous airflow can prevent depleting the CO₂
Good airflow can also help with cooling the air temperature.