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Temperature is the one setting you can’t see in a tray. You can see light. You can feel when the mix runs dry. A room that sits a few degrees too cold looks just like a room that’s right, until the seed comes up slow.
Humidity hides the same way. Too little and the leaves go limp. Too much, with warm air that barely moves, and you get the fuzzy white growth every grower dreads.
The good news is that microgreens aren’t fussy. Most crops share one comfortable range. The research shows where that range holds and where some crops ask for something different.
Key Takeaway
Most microgreens grow best in the 60°F to 75°F (15°C to 24°C) temperature range. The sweet spot ensures they germinate efficiently, soak up sunlight for photosynthesis, and grow into healthy plants. So, if you want your microgreens to flourish, you’ve got to keep an eye on those temperature and humidity levels.
Read on for the temperatures trials found for sprouting and growing, and how to keep humidity from turning into mold.
What temperature do microgreens need to grow?
Aim for a room between 15.6 and 21.1°C (60 and 70°F) once your trays are growing. That’s the air temperature Penn State Extension gives for microgreens. For germinating seed, it puts the soil a little warmer, at 15.6 to 23.9°C (60 to 75°F) (Sánchez & Berghage, 2025).
Research growers land in the same place. Look at how scientists set up their growth rooms and the numbers repeat. Kale and mustard microgreens grew at 21°C (69.8°F) by day and 17°C (62.6°F) at night in one trial (Brazaitytė et al., 2021). Four Brassica crops grew at about 21°C (69.8°F) in another (Ying et al., 2020). A third trial ran 25°C (77°F) by day and 20°C (68°F) at night (Flores et al., 2024).
Notice the pattern in those trials. Days run warmer and nights a few degrees cooler. A home grow space does that on its own when the heat drops overnight, so a small swing is normal. What hurts a tray is a big swing, or a room that stays well outside the range for days.
Where you put the tray matters as much as the thermostat. A shelf near a door or a heating vent can run several degrees off from the middle of the room. For more on setting up a space, see our guide to microgreens growing conditions.
What temperature do microgreen seeds need to germinate?
Seed is more forgiving than most growers think. Temperature changes how fast it sprouts far more than whether it sprouts at all.
One 2025 study germinated rocket (arugula) and radish seed for microgreens at eight temperatures, from 5 to 35°C (41 to 95°F). In plain water, rocket sprouted at 84% or better at every temperature. It did best from 8 to 20°C (46.4 to 68°F). Radish topped 94% from 15 to 25°C (59 to 77°F), and it still beat 75% at 5°C (41°F) (Toscano et al., 2025).
Speed told a different story. Both crops sprouted faster as the dish warmed from 5 to 25°C (41 to 77°F). At 25°C (77°F), rocket took about a day and a half on average and radish about two days. Going warmer than that didn’t speed either one up (Toscano et al., 2025).
So a cold room rarely kills your seed. It slows it down. Slow, uneven germination means a tray that grows at two different heights and is hard to harvest in one cut. In a cool basement or garage, a seedling heat mat under the tray brings the mix up to speed. Pick one with a thermostat so it can’t cook the seed.
Not every crop fits the cool-season mold. Millet is a warm-weather grass, and its microgreens behaved like it. Six millets germinated and yielded best at 35°C (95°F), and seedlings lost vigor at 15°C (59°F) and at 40°C (104°F) (Sadayandi et al., 2025). If you grow a warm-season crop, give it more heat than your brassicas.
Germination usually happens under cover, in the dark. Here’s why the blackout stage matters and how long to keep trays covered.
Do microgreens grow better warm or cool?
Warmth buys you size. But it can cost you flavor and nutrition. So the right number depends on what you want from the tray.
Hemp microgreens grown in an aeroponic system show the trade. At 28°C (82.4°F), they made 46% more shoot mass than cooler trays. The same warm trays had 33% less vitamin C and 22% less sugar (Vetchinnikov et al., 2025).
Heat changes shape too. Mustard microgreens stretched taller at 28°C (82.4°F) than at 18°C (64.4°F), no matter which light color they grew under. Arugula responded to light color instead. Blue light made it stretch, and more so at the cooler 18°C (64.4°F) (Kong et al., 2023).
Tall isn’t always bad. Some buyers want long stems. But a tray that stretches fast can flop, and leggy greens look tired in a clamshell. If your trays keep stretching, a slightly cooler room is worth trying before you change anything else. Our guide to microgreens lighting covers the light side of stretching.
Cool nights can help with more than shape. Fenugreek microgreens grown at 22°C (71.6°F) by day and 17°C (62.6°F) by night, under long days of light, gained about 22% in height and 20% in chlorophyll (Kumar et al., 2024). Light hours changed in that trial too, so temperature can’t take all the credit.
What happens if microgreens get too cold or too hot?
Too cold, and everything slows down. Seed takes longer to sprout, and growth drags. In the germination study above, the coldest dishes were the slowest by far (Toscano et al., 2025). A cold tray isn’t a dead tray. It’s a late one, and late trays throw off a harvest schedule.
Too hot brings two problems. The first is stretching, as the mustard trial showed. The second is disease. Penn State Extension notes that damping-off is favored by warm, humid conditions. It’s the only disease or pest its hydroponics class has run into with microgreens (Sánchez & Berghage, 2025).
Moving air is the simplest fix for heat that builds up around trays. A small fan keeps warm, wet air from sitting on the leaves. Clip-on or shelf fans that run quietly all day work well on a grow rack. Here’s our full guide to microgreens airflow.
What humidity do microgreens need?
No study has pinned down one best humidity for microgreens. But the trials themselves give a clear working range. Research growth rooms keep relative humidity between about 50 and 80% as microgreens grow.
Turnip greens and amaranth grew at 50 to 60% (Toscano et al., 2021). Kale and mustard grew at 60% (Brazaitytė et al., 2021). Four Brassica crops grew at 73% (Ying et al., 2020), and another eight cultivars at 79% (Flores et al., 2024). All of those trays came out healthy enough to measure.
Dry air is the risk at the low end. In one trial, lettuce microgreens grew on a gel instead of soil. At 50% and 30% humidity, the plain gel couldn’t keep leaf water above 88%. A version mixed with biochar held it above 90% (Tang & Tan, 2026). The lesson for a home grower is simple. In dry air, a growing mix that holds water does a lot of the work for you.
If your home runs dry in winter, a few tools help. A mister wets seed evenly during germination. A humidifier can lift a whole grow room. The one below is built for greenhouses and large rooms, so it’s sized for commercial racks, not a single shelf.
Can high humidity cause mold on microgreens?
Yes, and it’s the problem most growers meet first. The usual culprit is damping-off. Seedlings collapse at the base, and you may see white fuzz on the mix. Penn State Extension links it to warm, humid conditions (Sánchez & Berghage, 2025).
It can wipe out a tray. In a beet microgreen trial, a Pythium water mold added to the growing mix caused damping-off in 96% of seedlings from untreated seed. Coating the seed with a helpful Trichoderma fungus cut that to 19%. With a lighter dose of the mold, it fell to 5% (Pill et al., 2011).
You don’t need a lab to lower the risk. Keep leaves dry. Penn State recommends watering from below, as with an ebb-and-flow tray. It keeps leaves and stems dry, which helps avoid disease (Sánchez & Berghage, 2025). Mesh-bottom trays nested in a solid tray make bottom watering easy.
Then keep the air moving and avoid warm, still corners. If you water on a timer, our post on automated microgreens watering systems shows the setups. For the food safety side of growing, see the microgreens safety research hub.
How do you check temperature and humidity where microgreens grow?
Measure at the tray, not on the wall. The thermostat in your hallway tells you about the hallway. A shelf near the floor and a spot under a warm light can run a few degrees apart.
A small digital meter that reads both temperature and humidity does the job. Set it at leaf height in the middle of your trays and leave it there for a day. Check the low reading overnight and the high reading in the afternoon. That swing tells you more than any single number.
Wireless meters save you the trips. They send readings to your phone and keep a history, and some will alert you when the room drifts out of range. That’s handy for a grow space in a garage or basement you don’t visit every hour.
Once you know what your space really does, the fixes are small, like a heat mat for cold seed or a fan for still, warm air. Change one thing at a time and watch the next tray.
Wrap-up: what temperature and humidity do microgreens need?
Keep your grow space near 15 to 24°C (60 to 75°F), with the seed a little warmer than the air as it sprouts. Expect cold to slow a tray and heat to stretch it. Hold humidity in the range research rooms use, and keep the air moving so damp, warm corners can’t feed mold.
Temperature is one of several things that decide how a tray turns out. For the rest of the picture, from seed to harvest, start with growing microgreens: what actually controls a tray.
260 studies on temperature and growing stress
This guide cites 11 studies. Our research database holds many more on temperature and other growing stress. Here are the newest on temperature and humidity.
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The list updates on its own each week as new papers come out.
Microgreens temperature and humidity: frequently asked questions
Can you grow microgreens in a cold basement?
You can, but plan on slower trays. Cold air delays sprouting more than it stops it, so the main cost is time. A thermostat-controlled heat mat under the trays during germination closes most of that gap. Watch for still, damp air near the floor, where mold likes to start.
Should the temperature drop at night?
A small drop is fine and may even help. Many research growth rooms dim the lights and let the room cool by a few degrees overnight, like the kale and mustard trial above. Big swings are the thing to avoid.
Do microgreens need a humidity dome?
Only during germination. A cover or a second tray on top holds moisture around the seed and keeps it dark. Once the shoots are up and green, take it off so air can reach the leaves.
What humidity is too high for microgreens?
There’s no single cutoff in the research. Trouble rises when high humidity pairs with heat and still air. That’s the mix damping-off likes. If you see fuzz on the mix or stems collapsing, lower the humidity, add a fan and switch to watering from below.
Is a heat mat or a space heater better for microgreens?
For seed, a heat mat. It warms the mix where germination happens. A space heater warms the whole room, which matters more once trays are up and growing in a cold space.
References
Want to go deeper? The Microgreens World research database holds 250+ studies on temperature and growing stress in microgreens. Search the papers →
Brazaitytė, A., Miliauskienė, J., Vaštakaitė-Kairienė, V., Sutulienė, R., Laužikė, K., Duchovskis, P., & Małek, S. (2021). Effect of Different Ratios of Blue and Red LED Light on Brassicaceae Microgreens under a Controlled Environment. Plants, 10(4), 801. https://doi.org/10.3390/plants10040801
Flores, M., Hernández-Adasme, C., Guevara, M. J., & Escalona, V. H. (2024). Effect of different light intensities on agronomic characteristics and antioxidant compounds of Brassicaceae microgreens in a vertical farm system. Frontiers in Sustainable Food Systems, 8, 1349423. https://doi.org/10.3389/fsufs.2024.1349423
Kong, Y., Masabni, J., & Niu, G. (2023). Effect of Temperature Variation and Blue and Red LEDs on the Elongation of Arugula and Mustard Microgreens. Horticulturae, 9(5), 608. https://doi.org/10.3390/horticulturae9050608
Kumar, A., Singh, N., & Joshi, R. (2024). Deciphering the metabolic signatures of Trigonella microgreens as a function of photoperiod and temperature using targeted compound analysis and non-targeted UHPLC-QTOF-IMS based approach. Food Research International, 176, 113834. https://doi.org/10.1016/j.foodres.2023.113834
Pill, W. G., Collins, C. M., Gregory, N., & Evans, T. A. (2011). Application method and rate of Trichoderma species as a biological control against Pythium aphanidermatum (Edson) Fitzp. in the production of microgreen table beets (Beta vulgaris L.). Scientia Horticulturae, 129(4), 914–918. https://doi.org/10.1016/j.scienta.2011.05.018
Sadayandi, G., Thiruvengadam, T., & Thamenthiran, Y. (2025). Temperature-Dependent Variations in Growth, Agronomic Traits, and Sensory Attributes of Millet Microgreens. Madras Agricultural Journal, 112, 173–181. https://doi.org/10.29321/maj.10.se1228
Sánchez, E., & Berghage, R. (2025, December 16). Growing microgreens. Penn State Extension. https://extension.psu.edu/growing-microgreens
Tang, R., & Tan, J. (2026). Biochar-phytagel hydrogel enhances growth, nutrient uptake, and drought resilience of lettuce microgreens. Journal of Agriculture and Food Research, 25, 102573. https://doi.org/10.1016/j.jafr.2025.102573
Toscano, S., Cavallaro, V., Ferrante, A., Romano, D., & Patané, C. (2021). Effects of Different Light Spectra on Final Biomass Production and Nutritional Quality of Two Microgreens. Plants, 10(8), 1584. https://doi.org/10.3390/plants10081584
Toscano, S., Romano, D., Cafaro, V., & Patanè, C. (2025). Annual Garden Rocket and Radish as Microgreens: Seed Germination Response to Thermal and Salt Stress. Agronomy, 15(2), 361. https://doi.org/10.3390/agronomy15020361
Vetchinnikov, A., Uromova, I., Novik, I., Druzhkova, O., Dydykina, M., & Zhadaev, A. (2025). The effect of air temperature on the growth and development of hemp microgreens grown using aeroponics. E3S Web of Conferences, 613, 02004. https://doi.org/10.1051/e3sconf/202561302004
Ying, Q., Kong, Y., & Zheng, Y. (2020). Growth and Appearance Quality of Four Microgreen Species under Light-emitting Diode Lights with Different Spectral Combinations. HortScience, 55(9), 1399–1405. https://doi.org/10.21273/hortsci14925-20
