Martha tent sizing and setup checklist

Key takeaways

• A standard 4-tier Martha tent (about 27 x 19 x 63 in, roughly 500 L) holds about 16 five-pound blocks, or 12 with the fan on the top shelf. A 5-shelf tent holds about 20, or 16 with the fan on the top shelf.
• Size the tent by blocks and by which species can share one climate, not by strain count. Check the shelf load rating, which runs 20–50 lb by brand.
• Run an ultrasonic humidifier from a humidity controller to hold about 85–95% RH. Put the exhaust fan at the opposite end from the mist, on a cycle timer or CO2 controller, to keep CO2 under about 1,000 ppm, lower for oysters.
• Long, thin stems with small caps usually mean the tent needs more fresh air, or more light if it sits somewhere dark. Pins that form and then stall mean you should check humidity first.
• Switch the fan off, bag a block with sporulating mold where it sits, and carry it out unopened. Clean the empty tent between grows with detergent, then 70% isopropyl or undiluted 3% hydrogen peroxide.
• A tent costs about $150–480 to set up, but the blocks, not the tent, set most of your cost per pound.

Settings at a glance. Each figure is a starting point. The first column links to the section that explains it and cites its source.

Setting	Starting point	Source
Humidity	85–95% RH, toward the top while pins form (lion's mane 80–90% once growing); controller on at 88%, off at 93%	UC Cooperative Extension and North Spore; the 88/93 band is from our humidifier guide
CO2	Under about 1,000 ppm, lower for oysters (UC Cooperative Extension: under 600 ppm)	North Spore and UC Cooperative Extension; guides disagree on the exact ceiling
Fan cycle	2 minutes every hour, or 15 minutes every 4 hours, then adjust by what the stems show	GroCycle
Humidifier output	About 150–250 mL/hr of mist for a 4-tier tent	Our humidifier guide
Room temperature	60–80°F, out of direct sunlight	North Spore
Light	A cool-white (6500–9000K) LED strip, 12 hours on and 12 off, only if the tent sits somewhere dark	GroCycle

A Martha tent holds more blocks than a monotub or shotgun chamber without the cost of building a room. This guide covers sizing, shelf layout, humidity, fresh air and monitoring, then cleaning, costs and the signs you've outgrown the tent.

Jump to a section:

• What a Martha tent is
• Size and blocks per shelf
• Hardware checklist and setup order
• Airflow and fresh air
• Humidity and probe placement
• Stretched stems, stalled pins and cracked caps
• Monitoring temperature and humidity
• Cleaning and contamination
• Costs
• Tracking strains and flushes
• When to move up
• FAQ

What is a Martha tent, and who is it for?

A Martha tent is a wire shelving rack inside a zip-up plastic cover, used as a mushroom fruiting chamber. Most growers build one from a shelved mini greenhouse. The name comes from the first one, a Martha Stewart portable closet wrapped in clear plastic (GroCycle).

Covers come in a few kinds. Plain clear PVC (vinyl) lets you see in. Reinforced covers have a mesh grid inside the plastic. Christow calls its mesh-reinforced polyethylene (PE) cover stronger than standard PVC (Christow), and North Spore's BoomRoom II uses reinforced vinyl (North Spore — affiliate link: we may earn a commission at no extra cost to you). Reinforced covers are translucent rather than clear, which is fine, because mushrooms need little light. Skip models with a mesh "screen roof" unless you plan to seal it.

A Martha tent suits growers who have had success with kits, single bags or a shotgun chamber and want to fruit more at once. North Spore says beginners and growers with limited space may prefer a monotub, and experienced growers after higher yields a tent. It also names the trade-off: losing one monotub to contamination is not the same as losing a whole tent (North Spore — affiliate link: we may earn a commission at no extra cost to you).

A Martha tent is for fruiting, not incubation. GroCycle says the tents work best with substrate that is already fully colonized, so colonize your bags and jars somewhere else first.

What size Martha tent do you need?

Choose a Martha tent by how many blocks you fruit at once. A 4-tier tent holds about 16 five-pound blocks and a 5-tier about 20, or four fewer with the fan on the top shelf. Most Martha tents share a footprint of about 27 x 19 in; extra shelves make them taller or more tightly spaced, not wider. North Spore lists its 5-shelf 27 x 19 x 63 in tent at 18 cu ft, about 510 L (North Spore — affiliate link: we may earn a commission at no extra cost to you).

Volumes are approximate, based on real products' listed dimensions and volumes rather than the rounded sizes shown. Some 5-shelf tents fit a fifth shelf into the 63 in frame with closer spacing; others are about 76 in tall. The extra-wide row is the Gardman 7600 (True Value). Measure your closet or corner, height included, before you order.

How many blocks fit on each shelf?

A Martha tent shelf holds about four 5-lb fruiting blocks. North Spore rates each 25.5 x 17.5 in shelf of its tent at "20lbs or 4 fruiting blocks", with 12.5 in between shelves (North Spore — affiliate link: we may earn a commission at no extra cost to you). Load ratings vary by brand: Midwest Grow Kits rates its frame at 50 lb per shelf (Midwest Grow Kits). Check yours before you load a shelf with wet trays.

Two layout details change the count:

• The fan shelf. Most DIY builds put the exhaust fan on the top shelf. North Spore advises against putting trays on the shelf with the fan, because they block airflow and spore filtration (North Spore). With an in-tent fan, a 4-tier tent fruits about 12 blocks.
• Monotubs. A lidless monotub takes a whole shelf. A 66-qt latch tote is 13 7/8 in tall (Sterilite), so it won't fit between North Spore's 12.5 in shelves unless you take a shelf out. Measure your own tent's spacing first.

Can every strain share one tent?

Only species with similar needs can share a Martha tent, because the tent has one climate. North Spore notes that species "cannot all be grown together", and gives shiitake as an example that prefers it cooler and wetter (North Spore). Our fruiting temperature guide gives target ranges for oysters and lion's mane.

To compare strains, spread each strain across shelves rather than giving it a shelf of its own. Then a warm or dry shelf can't pass for a weak strain. Mississippi State Extension gives the same rule for farm trials (Mississippi State Extension).

What hardware does a working Martha tent need?

A working Martha tent needs a tent, a humidifier, a humidity controller, an exhaust fan with a timer, and a drip tray. Here is the checklist, with what each part does:

• Tent with frame and zip cover. Most kits include the wire shelves, so you don't need a separate rack.
• Ultrasonic humidifier. Size it with our humidifier guide: about 150–250 mL/hr of mist for a 4-tier tent. Feed it distilled or RO water, because ultrasonic units throw tap-water minerals into the air (EPA).
• Humidity controller. The controller reads a probe inside the tent and switches the humidifier on at a low setpoint and off at a high one.
• Exhaust fan. A small fan works for a 4-tier tent. A 4-inch inline fan on a speed controller gives you more room to adjust. If you can't duct it out a window, clamp a filter over the fan's exhaust to catch spores, as GroCycle's and North Spore's builds do.
• Repeat-cycle timer or CO2 controller to run the fan.
• Drip tray or tarp under the whole tent to catch condensation. Keep plugs and power strips out of it, as North Spore advises. Plug the humidifier, fan and controller into a GFCI-protected outlet or a plug-in GFCI, which the CPSC recommends wherever electrical equipment is near water (CPSC).
• Hygrometer for a second reading and for checking shelves. A model that records highs and lows, or logs to your phone, shows the overnight dips the symptom table asks about.
• A spot that holds temperature. The tent has no heating or cooling of its own. North Spore suggests a place out of direct sunlight that stays between 60 and 80°F (North Spore). Our fruiting temperature guide gives species ranges.
• A light, only if the tent sits somewhere dark. Most gourmet species use light as a cue to fruit and form normal caps. UF/IFAS says oyster fruiting "is triggered by light and lower temperatures" (UF/IFAS). In a closet, add a cool-white LED strip on a 12-hours-on, 12-hours-off timer; GroCycle suggests 6500–9000K (GroCycle).

In what order do you set it up?

Set up a Martha tent in this order once you have the parts:

1. Place the tent on its drip tray or tarp, out of direct sunlight, somewhere that stays between 60 and 80°F.
2. Plug in safely. Run the humidifier, fan and controller from a GFCI-protected outlet, with plugs and power strips out of the tray.
3. Put the mist and the exhaust at opposite ends of the tent (airflow layout).
4. Hang the humidity probe at canopy height in the middle of the tent, out of the mist (probe placement).
5. Set the controller to switch the humidifier on at 88% and off at 93% RH (humidity).
6. Set the fan timer to 2 minutes every hour, or 15 minutes every 4 hours (fresh air).
7. Add a light on a 12-hours-on, 12-hours-off timer if the tent sits somewhere dark.
8. Load fully colonized blocks, about four to a shelf, and keep trays off the fan's shelf (blocks per shelf).

Why ultrasonic, and why a controller?

An ultrasonic humidifier keeps misting when the tent is near 90% RH, where an evaporative (wick) humidifier slows down, and a controller keeps it from misting nonstop. Water evaporates more slowly as air nears saturation. The controller runs the humidifier between your on and off setpoints, so the tent holds a band instead of overshooting and wetting the blocks. North Spore and GroCycle both build their tents around an ultrasonic unit on a humidity controller (GroCycle, North Spore — affiliate link: we may earn a commission at no extra cost to you).

If you use a dual-outlet controller such as the Inkbird IHC-200 (Inkbird), don't run the fresh-air fan from its second outlet. That outlet switches on only when humidity climbs above your setpoint, so it can dump excess moisture but won't give you scheduled fresh air.

Compare humidifiers by output in mL/hr (one US gallon a day is about 158 mL/hr), not by room-size ratings. Room-size ratings are for humidifying a house, where EPA advises staying at or below 50% RH (EPA), not a tent near 90%.

Which fan, and where does it go?

Pick a humidity-rated fan and mount it at the opposite end from the mist, outside the tent on a short duct where you can. Most inline fans aren't built for fog, so check the rating. AC Infinity rates its CLOUDLINE S4 and A4 fans for 35–85% RH and its humidity-proof CLOUDLINE H4 for 35–95% RH.

Any 4-inch inline fan moves far more air than a tent needs at full speed. A 200 CFM fan moves the air of a 500 L tent about 11 times a minute. A University of California Cooperative Extension guide gives oysters 4–6 air changes an hour while they crop (UC Cooperative Extension). So run a big fan on a low setting and short cycles, not flat out.

How should you lay out airflow and humidity?

Put the mist in at one end of the tent and the exhaust at the other, so the fan pulls the mist across every shelf on its way out. Keep blocks out of the mist's direct path, as North Spore advises, so they don't get soaked. North Spore's and GroCycle's DIY builds put the humidifier at the bottom and the exhaust fan on the top shelf (North Spore — affiliate link: we may earn a commission at no extra cost to you). North Spore's BoomRoom II flips it, misting in at the top and exhausting at the bottom (North Spore — affiliate link: we may earn a commission at no extra cost to you). Either works. Mist and exhaust at the same end don't.

Fog doesn't climb on its own. Ultrasonic mist is fine droplets, and the fan's airflow decides where it goes. With the fan off, it hangs in the air and slowly settles.

Why run the tent under negative pressure?

Run the tent under negative pressure so spores and CO2 leave through the fan's filter or a duct. The fan pulls air out, and fresh room air leaks in low. North Spore and GroCycle both prefer it (North Spore — affiliate link: we may earn a commission at no extra cost to you). GroCycle adds that a fan pushing air in blows spores out through the gaps in the cover. Duct the exhaust to a window if you can; GroCycle notes that some people develop allergies after long exposure to oyster mushroom spores.

An intake filter is optional. A dense one, such as HEPA, needs a proper inline exhaust fan to pull air through it; a small PC-style fan can't.

How much fresh air does the tent need?

A Martha tent needs enough fresh air to keep CO2 under about 1,000 ppm, and lower for oysters; outdoor air is about 426 ppm (NOAA). The UC Cooperative Extension guide keeps oysters under 600 ppm and shiitake under 1,000 ppm while they crop. North Spore lists under 1,000 ppm for fruiting blue oyster (North Spore — affiliate link: we may earn a commission at no extra cost to you). For lion's mane it lists under 1,000 ppm while fruiting and 500–700 ppm while pinning (North Spore — affiliate link: we may earn a commission at no extra cost to you). Guides disagree on the exact ceiling.

You don't need a CO2 meter to start. GroCycle starts the fan at 2 minutes every hour if your timer has 1-minute steps, or 15 minutes every 4 hours if it only has 15-minute steps, then adjusts. North Spore describes its BoomRoom II fan as giving "a constant supply of fresh air" instead. Whichever you use, adjust by what the stems show.

A CO2 controller is the most precise option: it runs the fan only when CO2 climbs past your setpoint. Inkbird's ICC-500T costs $159.99 (Inkbird). Its sensor is rated to 95% RH, non-condensing, so mount it like the humidity probe, out of the mist.

Size the fan and humidifier together

Fresh air and humidity pull against each other, because every bit of room air the fan pulls in has to be brought up to fruiting humidity. We made a rough estimate from saturation vapor density at 20°C (HyperPhysics). A fan moving 50 CFM of 68°F, 40% RH room air around the clock would need about 700 mL/hr of mist to hold 90%. That's several times the 150–250 mL/hr that suits a 4-tier tent. North Spore makes the same point more simply: run the fan faster and you'll refill the humidifier more often (North Spore — affiliate link: we may earn a commission at no extra cost to you).

What humidity should a Martha tent run at?

A Martha tent should run at about 85–95% RH, toward the top of that range while pins form. The UC Cooperative Extension guide gives oysters 95% RH to pin and 85–92% while they crop. North Spore lists 95–100% for blue oyster pins and 85–95% for the growing mushrooms (North Spore — affiliate link: we may earn a commission at no extra cost to you). For lion's mane it lists 80–90% once it's growing.

Vendor controller settings start lower than that: GroCycle switches the humidifier on at 80% and off at 90%, and North Spore's Martha guide at 70% and 90%. To stay inside the 85–95% target, use the tighter band from our humidifier guide: on at 88% and off at 93%, with short mist bursts, which avoids overshoot.

Where does the humidity probe go?

Hang the humidity probe at canopy height in the middle of the tent, out of the mist stream and off the plastic wall. A sensor with water on it reads the water, not the air. Sensirion, which makes the sensor chips in many hygrometers, says liquid water makes its sensor "non-responsive to RH changes in the air" (Sensirion). So a probe in the fog reads high and shuts the humidifier off early. North Spore puts its probe on the top shelf, "slightly to the side so it's not directly in line of the humidifier's fog".

What does condensation on the walls tell you?

Condensation on the walls is a rough cue, not a hygrometer. Water beads on a surface colder than the air's dew point (University of Minnesota), the temperature at which that air would be saturated (National Weather Service). By our calculation, at 70°F and 90% RH that's a wall only about 3°F cooler than the air. A tent in a cool room fogs its walls at a lower humidity than one in a warm room, so use the probe for the number.

Water running down the walls onto blocks does mean the tent is too wet and too little air is moving. Watch the caps too: Penn State Extension finds bacterial blotch where caps stay wet for 4 to 6 hours or longer (Penn State Extension).

What do stretched stems, stalled pins and cracked caps mean?

In a Martha tent, long, thin stems usually mean too much CO2, stalled pins mean low humidity, and cracked caps mean the air is too dry. Use this table as a first check, then confirm with the probe.

What you see	Likely cause	What to do first
Long, thin stems with small caps	CO2 too high, or too little light	Add fresh air; check that the tent gets some light
Fuzzy stems	Too much CO2 or moisture	Add fresh air
Pins form, then stall or shrivel	Humidity low or dipping, often overnight when the humidifier runs dry	Check the RH log and the water tank; then cut any draft blowing on the blocks
Cracked or browning caps	Drying: low humidity or air blowing across the caps	Raise RH, or lower the fan speed and shorten the cycles
Water sitting on caps, wet spots	Too wet, with still air	Cut the mist, add gentle air movement, keep the temperature steady

The table follows GroCycle and North Spore, which tie skinny stems to high CO2 and stalled pins or cracked caps to low humidity (GroCycle, North Spore — affiliate link: we may earn a commission at no extra cost to you). A Mushroom Business advisory on button mushroom beds adds that too much dry air blown over them stalls the pins (Mushroom Business). Heat can abort pins too, so rule out temperature as well. For blocks that won't pin at all, or pin on the sides of the bag, see why mushrooms aren't pinning.

How do you monitor temperature and humidity in a Martha tent?

Monitor a Martha tent with one probe or logger at canopy height in the middle of the tent, and check the other shelves now and then. The fixed probe is your steady reference from flush to flush. Shelves can differ, though. Which shelf runs warmer or wetter depends on where your humidifier, fan and lights sit. In Penn State's study of mushroom production rooms, the bottom trays were the coolest and driest under two of three air layouts (Penn State).

Temperature differences move the humidity reading too. At 90% RH, a 1°C (about 2°F) difference shifts relative humidity by roughly 5 points with the same moisture in the air (Sensirion).

How do you check the shelves?

Check the shelves with a second hygrometer:

1. Compare the two meters side by side for an hour and note the difference. The TempPro (formerly ThermoPro) TP49 is rated ±3% RH above 80% (TempPro), so two cheap meters can disagree by several points.
2. Survey the tiers. Move the second hygrometer from shelf to shelf, letting it settle on each.
3. Decide. If the shelves agree within about 2°F and a few points of RH, one probe is enough. If the bottom shelf runs cool, raise the tent off a cold floor. Unless you're comparing strains, you can also put strains that like it warmer or cooler on the shelf that suits them.
4. Recheck when you move the humidifier or fan, or when the season changes.

In Penn State's button-mushroom rooms, more uniform conditions didn't give more or better mushrooms, though the mushrooms grown in the coldest, driest air were the poorest. So permanent probes on every shelf are optional; the survey is there to catch a shelf that runs too cold or too dry.

How accurate is a hygrometer at 90% RH?

A hygrometer at 90% RH is less accurate than its label suggests, and capacitive sensors can read a few points high after days in humid air (Sensirion). So hold a band, not a single number, and treat readings in the high 90s as approximate.

To find a meter's offset, seal it in a container with a small cup of table salt, dampened until it's wet through but no water pools. Saturated salt holds about 75% RH (Greenspan, National Bureau of Standards). Leave it at a steady temperature at least overnight, until the reading stops changing, then note the offset. The test checks only 75%, not the 90% your tent runs at.

Why log conditions instead of spot-checking?

A logger records the whole curve, including the dips between humidifier cycles and overnight, where a spot check shows one moment (Greenhouse Grower). For temperature, a probe in the substrate tells you more than air readings alone; see our fruiting temperature guide.

Our own sensor, Hypha Aeris, logs CO2, temperature and humidity for the zone it sits in. It isn't for sale yet; reservations are planned for 2027. We're aiming for around $160 at full retail for Gen 1, though final pricing isn't set yet. With an Aeris in the zone, each block's Grow Summary in Hypha shows the conditions in the zones it lived in, stage by stage. On the free plan you see the last 7 days of sensor history, including in the Grow Summary; Pro shows all of it. Hypha works without any hardware, and it can't take readings from other brands' sensors yet.

How do you keep a Martha tent clean?

Keep a Martha tent clean by emptying it between grows, scrubbing every surface with detergent and water, then disinfecting with 70% isopropyl or 3% hydrogen peroxide. Scrub before you disinfect: organic material shields microbes from disinfectants (CDC), and mold on hard surfaces comes off with detergent and water (EPA).

Between grows:

1. Unplug the humidifier, fan and lights. Alcohol is flammable, so let every surface dry and air the tent out before you plug them back in.
2. Empty the tent. Pull out spent blocks and debris, and take out or cover the humidity probe. Sensirion lists isopropanol among the substances that can contaminate its humidity sensors or even damage them irreversibly (Sensirion).
3. Scrub the shelves, walls and drip tray with detergent and water, then let them dry.
4. Disinfect every hard surface. Use 70% isopropyl alcohol: spray, leave it at least 30 seconds, then wipe. Or use ordinary 3% hydrogen peroxide, undiluted, kept wet for several minutes. The CDC calls 3% peroxide "stable and effective" on surfaces, and weaker solutions need longer contact (CDC).
5. Clean the fan blades and grille, the light strip and the probe housing, which all collect spores. Wipe the probe housing with a dry or damp cloth, not alcohol.
6. Clean the humidifier as our humidifier guide describes.

During a grow, spot-clean drips and debris with a cloth rather than misting disinfectant inside a loaded tent. Keep alcohol and peroxide off blocks, pins and fruit. Penn State Extension recommends spraying alcohol on mushrooms infected with dry bubble to kill them, so it kills healthy ones too (Penn State Extension). Empty the drip tray and wipe it dry whenever water pools.

Keep the surfaces in the tent smooth and wipeable, with no wood or cardboard shelf liners. In a study of mushroom-farm surfaces, Trichoderma spores persisted more on rough wood and concrete than on smooth glazed tile (PubMed).

What do you do with a contaminated block?

A block with sporulating mold comes out of the tent right away, unopened. North Spore says to remove green mold immediately, before it spreads. For sporulating orange mold, it says to seal it in a bag without disturbing it, because disturbing it releases a cloud of spores (North Spore — affiliate link: we may earn a commission at no extra cost to you). Moving air spreads spores: writing about cobweb mold, Penn State Extension warns that "very little air movement is required to dislodge spores" (Penn State Extension).

So put on an N-95 respirator, gloves and eye protection first, EPA's minimum protection when disturbing mold (EPA). Then switch the fan off, slip a bag over the block where it sits, seal it, carry it out of your grow space and throw it away unopened. North Spore advises sanitizing the area after disposal: wipe the shelf with a cloth dampened with 3% hydrogen peroxide, keeping it off nearby blocks.

Contamination isn't only green. North Spore lists green, blue, grey or black patches, and orange for Neurospora. It adds that on certain kinds of mycelium, a blue stain may be natural bruising rather than mold (North Spore — affiliate link: we may earn a commission at no extra cost to you). If you aren't sure, check it against our contamination ID guide; if you still aren't sure, treat it as contamination.

How do you track contamination?

Track contamination as a percentage per batch and per strain. Count incubation losses (contaminated blocks out of the blocks you inoculated) apart from tent losses (blocks that contaminate while fruiting, out of the blocks that went into the tent). Then look at the pattern.

A Cornell Small Farms guide with Fungi Ally says substrate or sterilization problems show up through an entire batch. Problems with air, surfaces or tools at inoculation show up spotty and inconsistent (Cornell Small Farms and Fungi Ally). So one batch failing while others on the same shelves stay clean points upstream, to its spawn and substrate. Our pink oyster grain spawn guide shows what contaminated spawn looks and smells like. Blocks from several batches going at once point at the tent: the humidifier, standing water, stale air or a missed cleaning.

On Hypha's free plan, the strain performance view shows each strain's contamination rate, separately for spawn and bulk. The rate counts finished blocks marked contaminated, out of all finished blocks, for blocks started in the last 90 days or for all time. Its bulk rate also counts bulk blocks that contaminated while still colonizing, so it isn't the tent-only number. Tag a block "suspect" while you watch it, and when you bag it out, finish it as Failed with the contaminated flag so it counts.

What does a Martha tent cost to build and run?

A Martha tent costs about $150–480 to set up and about $5 a month in electricity to run. Budget mushroom-supply parts come to about $150, mid-range parts about $300–340, and a turnkey kit $479. Prices below are from the makers' and vendors' own pages on 19 October 2026. Three budget parts were marked down from their list prices that day. At Midwest Grow Kits' list prices ($54.99 humidifier, $34.99 controller, $12.99 timer), the budget build is about $178.

Part	Budget	Mid-range
Tent with frame	Midwest Grow Kits 4-tier, $49.99	North Spore BoomRoom II, 5 shelves, $99.99
Humidifier	Midwest Grow Kits Mushroom Monsoon 3 L (no mL/hr rating published), $39.99	AC Infinity CLOUDFORGE T3, $69.99
Humidity controller	Midwest Grow Kits digital controller, $27.99	Inkbird IHC-200, $45.99, or none (the T3 has its own)
Exhaust fan	Midwest Grow Kits Fresh Air Amplifier (no humidity rating published), $24.99	AC Infinity CLOUDLINE H4, $99.00
Fan timer	Midwest Grow Kits 24-hour dial timer (30-minute steps), $8.99	North Spore repeat-cycle timer, $27.99
Total	about $152	about $297–343

The totals cover the parts in the table. Add a drip tray or tarp and a hygrometer (the TP49 was $9.99 on sale). Add a fan filter if you can't duct outside, and a light if the tent sits somewhere dark. A few notes on the parts:

• CLOUDFORGE T3. The T3 puts out 8.11 fl oz an hour, about 240 mL/hr, and has humidity triggers built in, read from a corded sensor probe (AC Infinity). AC Infinity rates it for 30–85% RH, so keep it outside the tent, run its mist tube in, and route the probe into the tent at canopy height. On its own it mists below one trigger point and stops above it, with no band to set (AC Infinity manual). Add the IHC-200 if you want one.
• Fresh Air Amplifier. Midwest Grow Kits says many growers mount it low as an exhaust; mounted high, it pushes air in instead (Midwest Grow Kits). So keep it low, and if your humidifier sits low too, run its mist tube up to the top shelf so mist and exhaust sit at opposite ends. The Mushroom Monsoon's tubing stretches to 66 in (Midwest Grow Kits).
• Timers. The budget build's timer switches in 30-minute steps (Midwest Grow Kits), so the shortest fan run it can give is 30 minutes. That's too coarse for either of GroCycle's fan schedules. A repeat-cycle timer can run 1–2 minute bursts: North Spore's runs from 5 seconds to 30 minutes on and up to 60 minutes off (North Spore). Swapping one into the budget build adds about $19.
• Turnkey. North Spore's BoomRoom II Automated system ($479) bundles the 5-shelf tent with a humidifier, humidity controller and fresh-air fan (North Spore — affiliate link: we may earn a commission at no extra cost to you). Its Myco-Mister II is an 80 W humidifier rated up to 2,000 mL/hr (North Spore — affiliate link: we may earn a commission at no extra cost to you). That's far more than the 150–250 mL/hr a tent this size needs. Run it in short bursts on the controller, and expect a bigger power bill than the estimate below.

What does it cost to run?

Electricity for a Martha tent runs about $5 a month. A 24 W humidifier misting half the day, a 4-inch inline fan running around the clock at about 20 W, and a humidity controller use about 0.85 kWh a day. At the US average residential rate of 18.31 cents per kWh in July 2026 (EIA), that's just under $5 a month. A fan on a cycle timer uses much less.

Water can cost more than power if you buy distilled water by the gallon. A humidifier rated at 240 mL/hr that mists half the day goes through about 3 L of water a day, roughly 23 gallons a month.

What is your cost per pound?

Cost per pound is your monthly costs divided by the fresh pounds you harvest that month:

Cost per pound = (build cost ÷ months you expect to use it + monthly electricity + water and supplies + blocks or substrate) ÷ fresh pounds harvested

Add your time if you want a farm-style number. Here is an illustrative example, not a benchmark:

• Tent and power. The $297 mid-range build spread over two years is about $12.40 a month. Add about $5 of electricity. Water and other supplies are left out of this example, so add your own.
• Blocks. Eight bought 5-lb blue oyster blocks at $18 each cost $144 (North Spore — affiliate link: we may earn a commission at no extra cost to you).
• Yield. Five specialty mushroom farms in a USDA-funded SARE study averaged 0.88 lb per 5-lb block they started, across species and counting lost blocks. SARE notes that most farms rotate blocks out every 2–4 weeks rather than leave them in for 8. Cornell's trial blocks in the same study, left to fruit for 8 weeks, gave 1.36–1.63 lb (SARE). Eight blocks at 0.88 lb give about 7 lb.
• Result. About $161 ÷ 7 lb ≈ $23 a pound before water and supplies. At 1.5 lb a block, about what Cornell's blocks gave, it's about $13 a pound.

The tent and power are only about $1.50–2.50 of each pound; the blocks are the rest. Making your own blocks, and getting more from each one, is what moves the number.

How do you track strains and flushes across tents?

Track each block's strain, parent, spawn date, dry substrate weight and shelf, and each flush's pin date, harvest date and fresh weight. Biological efficiency (BE) is the fresh weight of all flushes divided by the dry weight of the substrate, as a percentage (PMC). The UC Cooperative Extension guide gives oysters 100–200% and shiitake 50–145%. It can top 100% because you're comparing wet mushrooms to dry substrate. If you dry your harvest, log the dried weight too.

A spreadsheet works, but it gets messy once you're tracing blocks back through several generations of grain and culture across more than one tent. In Hypha, make each tent a zone, and tag each block with its shelf. Create each block as a transfer from the jar or bag it came from, so every harvest traces to its lineage; a parent can't be attached later. A flush records its date, fresh and dry weight, and notes.

Hypha's free plan holds 25 active blocks and one zone with a sensor; zones without a sensor don't count, so three tents fit as three zones. Every block counts as active until you archive it, including finished blocks and the grain jars and spawn bags behind your fruiting blocks, so a full tent can outgrow Free. Pro, $12 a month, raises that to 250 blocks and five monitored zones. It also adds cost per pound for blocks started from costed prep stock (pricing). That figure counts supplies and prep only, so add the tent, power and your time yourself.

Hypha doesn't record a pin date or work out biological efficiency, so note those yourself. It needs an internet connection to save an entry, with no offline mode yet, and it has no marketplace or shared strain library. For a comparison of other tracking apps, see our grow log guide.

When should you move up from a Martha tent?

Move up from a Martha tent when it's physically full, or when the room around it can't give it what it needs. A tent tops out at about 12–20 five-pound blocks, depending on its size and where the fan sits. Watch for these signals:

• Every shelf is full and blocks are waiting on the floor.
• No spot in your home holds the right temperature year-round. A tent has no heating or cooling of its own, so it's only as stable as the room it stands in. North Spore's tent kit comes without a heater (North Spore).
• Spores or damp still reach your living space after you've filtered the exhaust or ducted it outside.
• Chores eat your week. If refilling, hauling water and cleaning take more time than growing, a room with plumbed water and a drain starts to pay off.

Wide humidity swings aren't a reason to move up. They usually mean the controller needs the short mist bursts and 5–7 point deadband from our humidifier guide, not a bigger space.

What comes after a Martha tent?

If you've run out of shelves, the next step after a Martha tent is usually a second tent or a larger grow tent, not a built room. If the problem is temperature, a second tent won't fix it; the space it stands in needs heating or cooling. GroCycle names a larger hydroponics grow tent as the step up from a Martha (GroCycle). Several tents also let each one keep its own humidity, fresh air and light, and they make it easier to keep a contamination event to one tent.

A built room is a much bigger step. The Cornell and Fungi Ally guide sizes an 8 x 16 ft room at around 150 lb a week (Cornell Small Farms and Fungi Ally). A Transfarmation fruiting-room guide starts with a shell built to take constant humidity and frequent washing, ideally with a floor drain. It then covers temperature, fresh air, humidity and light (Transfarmation). Keep the room's humid air out of the rest of the house; EPA advises keeping indoor humidity below 60%, ideally 30–50% (EPA). Our grow room guide covers choosing the space, the walls and floor, fresh air, heating and safe wiring.

In Hypha, a new room is a new zone. Each block shows the zone it's in, and its history logs every move between zones. That way you can tell blocks that fruited in the tent from those that fruited in the room.

FAQ

What size Martha tent do I need for 10 strains?

The Martha tent size you need for 10 strains depends on how many blocks of each you fruit. Ten strains at two blocks each is 20 blocks, which fills a 5-shelf tent with the fan outside it; ten single blocks fit a 4-tier tent. Only species that like the same temperature and humidity can share a tent, so ten strains may need more than one.

Can I put a Martha tent in a closet?

Yes, you can put a Martha tent in most closets; North Spore says the tents also fit kitchens and basements. Measure the height first (a 4-tier tent is about 63 in tall), add a light, and filter the exhaust or duct it outside. The fan swaps tent air for closet air, so give the closet some air exchange too, such as a louvered door.

Do I need a humidifier, or will trays of water work?

A Martha tent with a fan needs a humidifier. GroCycle's low-tech build has no fan and no humidifier. A few small holes and a slightly open zipper let air in. A tray of wet perlite, or a spray bottle used a couple of times a day, keeps it humid (GroCycle). Replace a perlite tray when it smells or discolors, as you would any standing water. Once a fan pulls in fresh air, every air change has to be re-wetted, and trays can't keep up.

How much fresh air does a Martha tent need?

A Martha tent needs enough fresh air to keep CO2 under about 1,000 ppm, and lower for oysters. In practice, a low fan setting on a cycle timer does it; GroCycle starts at 2 minutes every hour. Add air if stems stretch, and check humidity first if pins stall. Don't aim the airflow straight at the pins.

Is a Martha tent better than a monotub?

A Martha tent is better than a monotub for growing more at once, and a monotub is better for starting small. North Spore says beginners and growers with limited space may prefer a monotub, and growers after higher yields a tent. A tent puts every block under one humidifier and one fan, which makes side-by-side comparisons easier, though shelves still differ. The trade-off is that one contamination can spread through the whole tent, where a monotub fails alone.