How to Make a Martha Tent Mushroom Fruiting Chamber

We created this comprehensive Martha tent set up and maintenance guide to help anyone interested in learning Martha tek or the Martha technique for mushroom growing. It includes step-by-step instructions for building a Martha setup, setting up and dialing in environmental controls (humidity, air flow, gas exchange, and spore filtration) and includes a troubleshooting guide for identifying potential issues with your grow.

Marthas are the surest way to grow consistent and beautiful flushes of mushrooms year-round. All in all, they’re a solid solution for beginner to intermediate mushroom growers working for a variety of species, growing techniques, spaces and budgets.

The following is our complete step-by-step process to building and maintaining your own Martha Tent, using materials you can find online or at your local hardware or hydroponic store.

Martha Tents are one of the most effective ways to fruit mushrooms indoors. Search any mushroom forum, Reddit page, or Facebook group and you'll find dozens of versions of Martha Tent builds few to none that are exactly identical. Although Martha Tents may come in all shapes and sizes, those who have found success in growing mushrooms attribute it to the ability to balance four conditions: humidity, fresh air exchange, temperature, and light.

Martha Tents control two of these conditions: humidity and fresh air exchange (for exhausting carbon dioxide), while the environment outside of the tent determines the temperature and light conditions. All in all, it’s a balancing act that only works if all four conditions are balanced and the environmental systems of your tent are working in tandem.

• Humidity: Mushrooms will dry out or not fruit at all if the environment is too dry. Therefore, humidity is dispensed and monitored by your humidifier and humidity controller to maintain a proper moisture content inside the Martha Tent.
• Fresh Air Exchange: Like humans, mushrooms inhale oxygen and exhale carbon dioxide. Meaning, if the air inside the tent isn’t constantly refreshed, they may suffocate. Excess carbon dioxide is exhausted by our fresh air exchange fan, allowing oxygen to freely circulate throughout the tent.
• Temperature: Most mushrooms fruit well in temperatures between 55-80 degrees Fahrenheit. It’s recommended to place your tent in a temperature controlled environment. Some builds will utilize heating pads or heated water humidifiers when the ambient temperatures of your tent’s environment are cooler than 55 degrees Fahrenheit.
• Light: Unlike plants, mushrooms don’t photosynthesize. However, they still require some ambient light in order to fruit properly. By placing your tent in an area with indirect light or supplemental lighting, it will help your mushrooms determine where to fruit and the color of their fruit bodies.

If you manage all four of these conditions properly, you will have beautiful mushrooms in no time.

Materials

• Greenhouse Tent
• Fresh Air Exchange Fan
• Ultra-Sonic Humidifier
• Humidity Controller
• Hose Clamp
• Poly Pre-Filter cut down to size
• Drip Tray

Optional

• 4 inch Ducting
• Foam (cut to fit a window)

The first step is to build your greenhouse tent. Ideally, you’ll want to use a greenhouse tent that has five shelves; if this isn’t the case, we suggest you remove the bottom shelf and place it at the top. If you decide to do this, you’ll want to reinforce the bottom of your tent to maintain its structural integrity. (Although we decided to use a transparent tent, some growers may opt to use an opaque stealth tent. Opaque tents work just as well as long as you install supplemental lighting at the end of the building process.)

There are a few reasons why we prefer to create extra shelf space at the top.

• It allows you to maximize the total grow space inside your tent
• It creates space at the bottom for your humidifier
• And lastly, your fresh air exchange fan will sit at the top, which will help pull humidity through the tent and exhaust CO2.

Once you’ve finished building your greenhouse tent, you’ll want to place it on top of a drip tray. This drip tray will help seal and capture any excess moisture. If you aren’t able to find a drip tray, you can simply use a folded tarp and clamps as an alternative.

The next step is to install your humidification system. You’ll need both your ultrasonic humidifier and the humidity controller, which will be used to monitor and control the ambient humidity inside the Martha Tent.

The ultrasonic humidifier will be placed at the bottom of the tent, with the electrical wires threaded underneath the bottom of the greenhouse plastic. Make sure that any electrical component is not sitting in the drip tray where it is more likely to have direct contact with water. Pro tip: Make sure to not place any mushrooms in the direct line of the humidifier if you decide to use the bottom shelf. This will ensure that your mushrooms are not oversaturated with water, and that the humidity is dispersed evenly throughout the tent.

Follow the specific instructions of your humidity controller for usage.

Start by setting the low range of humidity to 70% (meaning the humidification system will turn on when humidity drops to that level) and a high range of 90% (meaning the system will turn off when it hits 90%). This will make the average humidity around 85% which works well for the majority of grows. Make adjustments as needed if your mushrooms are showing signs of being either too dry or too wet. We’ll go over the symptoms of both conditions at the end of this article.

Alternatively, you may see some growers use an external humidification system that looks something like this:

This is a DIY humidification system that uses a pond fogger to generate humidity inside of the bin, while a computer fan pushes the humidity through a duct and into the tent. To make this system, cut two holes into the lid of a Tupperware bin with one hole sized to fit a computer fan and the other sized to fit 4 inch ducting. Position the computer fan to be pushing air into the bin. Attach both the ducting and fan to the lid with duct tape. The pond fogger should have a float ring that allows it to sit on top of the water inside of the bin. Thread the power cord out through the top and plug it into an outlet. You will need to cut an additional 3.5-4 inch hole into your greenhouse plastic near the bottom of the tent. Thread your 4 inch ducting through the hole and secure it with duct tape.

Although this system does work, there are a few drawbacks.

Though this system provides a large reservoir for water, pond foggers aren’t particularly reliable and tend to have fairly short lifespans. For this reason, we like to use the ultrasonic humidifier and refill it more often. This is up to your own personal preference.

The third step is to install your fresh air exchange fan. Because you’re exhausting air out of your tent, you’ll be making what is called a negative pressure system. This means you’ll be making a vacuum inside the tent. In a positive pressure system you’d be pushing fresh air into the tent causing it to balloon outwards, but this comes with the downside of losing the ability to direct spores and moisture out of a duct or through a filter.

Though you’ll see positive pressure builds elsewhere on the internet, we prefer negative pressure systems for a few reasons:

• You’re able to exhaust spores and CO2 outside of the tent
• As the air is filtered through the fresh air exchange fan, oxygen rich air is pulled in from the bottom of the tent

Simply place your fan on the top shelf, with the exhaust end facing the back of the tent. Run the wires down the back underneath the bottom of the greenhouse plastic.

Since you’ll be altering your tent to grow mushrooms, you’ll need to cut a hole in the back of the tent that’s big enough to fit your fan, but small enough to create a tight seal. Trace the inside of your fresh air exchange fan on the plastic of the tent with a sharpie, and then cut it out with some scissors.

Once you create an opening for your fan, gently guide your fan through the opening. At this point, your fresh air exchange fan should be able to balance upright on the top shelf.

The last step is to attach a filter to the back of your fresh air exchange fan to capture any excess spores so that they don’t permeate your living spaces. You can use a 4 inch hose clamp to attach your filter to the back.

Once you’ve attached the filter, you now have a fully functioning Martha Tent. Although this build works great inside closed spaces without access to a window, you can also choose to duct your spores outside a window if one is available using flex foil ducting.

Using ducting to exhaust the air outside of your Martha Tent is a good idea when there is a window available and your tent is placed in a home or living space. This is also a good idea for people who may be sensitive to spores or particulates in the air.

Building a duct is fairly simple. By placing your Martha Tent near a window (out of direct sunlight), you can attach a 4 inch duct to the back of the fresh air exchange fan, and seat the end of the duct through a fitted piece of foam. Be sure to remove any filters prior to installation.

And voila! You’ve finished building your very own Martha Tent!

As we discussed earlier, mushrooms rely on the fine balance between: fresh air exchange, humidity, temperature, and light. 

In some ways, the dynamic interaction between these conditions are what make mushroom growing a blend of art and science.

In the video tutorial, we placed our tent in a climate controlled out-building away from direct sunlight. Our spores and CO2 were ducted outside with the fresh air exchange fan - and our humidification system will maintained proper moisture content inside of our tent.

The placement of your tent may vary depending on your set-up, but this set-up can be replicated in a multitude of ways with a few minor adjustments.

• Just like humans, mushrooms inhale oxygen and exhale carbon dioxide.
• Since the Martha Tent is a sealed environment, without proper fresh air exchange carbon dioxide may build up inside your tent and suffocate your mushrooms.
• Installing a fresh air exchange fan allows you to exhaust excess CO2 and maintain proper levels of oxygen.

If you place trays of colonized mushroom mycelium inside of a closed tent without any alterations or fans for air exchange, your mushrooms would eventually suffocate due to high CO2 and lack of oxygen. This is because just like humans, mushrooms inhale oxygen while exhaling CO2.

Without constantly refreshing the air in the tent, the exhaled CO2 will build up and disrupt the mushroom growing process. This is why we installed our fresh air exchange fan. You can also use a carbon dioxide meter to get precise measurements of CO2 concentrations, though this isn’t necessary as long as you keep an eye on your mushroom growth, acknowledge symptoms of high CO2 (lack of growth, leggy stems, or coral like growth), and adjust accordingly.  

In the wild, lower levels of CO2 help indicate where a mushroom should fruit. Inside your grow tent, an abundance of fresh air will have the same effect. Just having great air exchange won’t guarantee beautiful flushes of mushrooms though. Without a system for managing ambient humidity your mushrooms will eventually turn brown, crack, or dry out due to overly dry air.

• Humidity ranges between 70-90%, depending on the species you're growing.
• Mushrooms may dry out or never grow if the environment lacks proper humidity.
• Conversely, mushrooms that are oversaturated with humidity may become soggy or have fuzzy stems.

Humidity is the next condition managed by your Martha Tent that influences mushroom growth.

Mushrooms are about 92% water, and for this reason, mycelium in the wild will wait until rainfall or humid conditions to produce mushrooms. So, along with a fresh air exchange fan, mushroom growers will add humidification systems in their tent in order to prevent mushrooms from drying out or not growing at all.

Fresh air exchange and humidity systems are the two primary components you’ll add to your Martha Tent. But, you’ll still have to account for the ambient conditions outside of your tent.

• Most mushrooms grow well between the temperature range of 55-80 degrees Fahrenheit.

Even with a fully built Martha Tent, most growers place their tents in areas that have some form of climate control. Regardless of the location you’ll want some control over the temperature surrounding your growing environment.

Under natural conditions, many mushrooms will fruit in response to seasonality, limiting the time period in which mushrooms grow. Growing mushrooms indoors year-round requires more consistent conditions.

Your tent should be placed in an environment that generally stays between 55-80 degrees Fahrenheit. Though keep in mind that the exact range tends to vary between mushroom species.

• Unlike plants, mushrooms don’t use light as an energy source. Though, they do need some light in order to determine where they will fruit and develop colorful fruit bodies.
• The smallest amount of light will work, whether it’s indirect light from a window or artificial.
• It’s generally advised to not place mushrooms in direct sun as it may raise the substrate, or growing chamber, to harmful temperatures.

Unlike plants, mushrooms don’t use light as an energy source to grow. But mushrooms are photosensitive; meaning the smallest amount of light helps determine the shape and color of the mushroom fruit bodies. Light can also trigger mushroom growth or indicate suitable fruiting environments. On the flipside, too much direct sunlight can cause your mushrooms to dry out or make it harder to control your other conditions.

Growers who place their Martha Tents in environments that lack light, such as a closet, will use supplemental lighting. Growers who place their tents in open living spaces will generally position it in an area away from direct sunlight.

So, fresh air exchange, humidity, temperature, and light are the four conditions of mushroom growing. By balancing all four, you can fruit beautiful flushes of mushrooms year round.

The best way to manage and adjust the conditions in your Martha Tent, is to observe how your mushrooms grow over time.

If you have skinny stems, or fruit bodies, or growth resembling coral, it could be because the carbon dioxide levels are too high.

If you have fuzzy stems, the cause could be excessive carbon dioxide or moisture.

If your caps are brown or cracked, it could be that there’s not enough humidity or that they were harvested too late.

If the fruiting bodies are pale, it could be because of a high temperature or because of a low light environment.

If there was no growth at all, it could be because of high carbon dioxide, high temperatures, or because your substrate wasn’t fully colonized, or because your substrate was too dry.

If your growth stopped after pinning, it could be due to low humidity, or a temporary drop in the humidity.