Is it getting hot in here, or is it just weed? Creating a comfortable environment or sticking to a grow room chart for cannabis temp and humidity is something many growers find challenging. When you're done reading this, you'll see how easy it can be. 

 

Without proper control of moisture levels, your greenery dehydrates, drowns, and eventually dies. Don't freak out; we've got life-saving tips to achieve optimum weed temp and humidity.

 

We discuss why humidity and temperature are so important and how to get them right to keep plants happy through all growing stages. 

 

Importance of maintaining optimal humidity and temperature for cannabis 

What is the best temperature and humidity for growing weed? To know how to optimize the ideal temp and humidity for cannabis and why it’s essential, you must first understand cannabis plants' respiration process. 

 

  1. During photosynthesis, plants must convert the sugars absorbed into energy to help the flora grow. 
  2. To transform sugar into energy, they must derive carbon dioxide from the air. 
  3. Carbon dioxide enters through the plants' pistils which function like tiny pores. 
  4. The intake of carbon dioxide causes flora to lose water to the environment. 
  5. Relative humidity dictates the amount of water loss your marijuana crops suffer. Extremely low levels cause plants to suck too much water from their roots, and extra high humidity leads to water retention below ground level. 

 

Temperature and humidity go hand in hand. If the former is off, your plants suffer even with optimal levels of the latter. The crops get damaged differently based on whether it's too hot or cold. 

 

Some cannabis seeds develop into plants that handle extremely warm or chilly climates. Generally, a grow room temp lower than 60°F and higher than 80°F causes heat stress and stunts the growth of most crops. 

 

If it's overly hot, cannabis becomes susceptible to root rot, heat burn, and reduction of terpenes and resin. When the temperatures are too cold, plants produce lower yields and are vulnerable to mold when paired with high humidity. 

 

Maintaining the ideal temperature and humidity for weed gives you generous harvests of vibrant colored buds with strong aromas and potent THC and CBD counts. Some strains turn a gorgeous purple shade with cold exposure, so maintaining optimal temperatures affects your final product.

 

Sticking to a chart for cannabis temp and humidity is essential because crops absorb enough moisture from the leaves when the levels are ideal. This process prevents them from storing excess water in the roots or struggling to hydrate and sucking moisture out of them and the stems. 

 

Ideal temp and humidity for weed growing

 

Factors affecting levels of humidity for weed plants 

Finding the perfect humidity in a grow room (relative humidity, or RH) is crucial for growing cannabis. Relative humidity (RH) refers to how much water vapor is in the air in an area. 

 

Here are the three main factors that affect your success in achieving the best temp and humidity for cannabis: 

 

Growing stages

Cannabis plants have three main growing stages; seedlings, vegetation, and flowering. Their roots, branches, and leaves develop and use water more efficiently as each phase progresses. The humidity for seedlings should be lower than for mature marijuana crops.

 

Climate and region 

Cooler regions have dry or less moist air, so you may have difficulty keeping humidity levels up if you live in a cold climate. 

 

Tropical areas or hot conditions tend to have higher humidity, even with low temperatures. Cannabis plants usually thrive in a humid climate, but an excess leads to mold buildup. If you are seeking for a strain that could thrive in cold areas, look at this collection of winter cultivars.

 

Genetics

Some cannabis species better handle hot or cold climates with low or high humidity. There are strains like Afghan Kush that do well in cooler temperatures thanks to their genetics. Some buds like the ones from Blue Dream feminized seeds thrive in high humidity and need hot temperatures to develop properly. If you want less work, pick a strain that suits your climate.

 

The four stages of the cannabis plant cycle

There's a specific temp and humidity for weed cultivation in each stage of your plant's life cycle. Every phase has unique metabolic reactions meaning they use energy differently, so the humidity levels either assist or deter their growth. 

 

Seedling stage

Seedlings are fragile with tiny roots, and extreme moisture quickly causes mold buildup and damages them. Their underdeveloped roots rely heavily on their leaves for hydration, so humidity plays a huge role in nourishing seedlings.   

 

It's essential to maintain the proper humidity for seedlings because they develop critical features of the cannabis plant in this phase. Seedlings sprout 3–13 finger leaves, eventually becoming the classic 5–7 finger marijuana leaves. 

 

Healthy seedlings and clones have short, thick foliage with vibrant green leaves that aren’t fully formed. Use a chart for cannabis temp and humidity to keep the climate humid enough for substantial root development and sufficient water uptake to the leaves. 

 

Here are our recommended temperature levels and humidity for seedlings:

 

  • High relative humidity: 65–70%
  • Day temperatures/lights on: 77°F 
  • Night temperature/lights off: 70°F

 

Vegetation period

In the vegetative stage, plants have stronger roots and perform efficient water uptake through evaporation. You can tell your seedlings have begun vegging when they develop several sets of pointed leaves. 

 

If you maintain the best temp and humidity for weed, plants grow rapidly at this stage. New well-structured leaves and branches, stronger nodes, and well-grounded roots develop. During vegging, cultivators typically begin defoliation because the growth is sometimes aggressive.

 

You can keep cannabis plants in vegetation for as long as you like since they need light cycle changes to trigger flowering. Autos begin blooming without manual interference, so the autoflower temperature and humidity chart differ from regular or feminized seeds. 

 

When vegging, cannabis plants develop stronger and more efficient root systems, helping them take in water easier. Lowering humidity during the vegetative stage prevents soggy roots, weak branches, nutrient lockout, and drowning. 

 

Reduce the humidity levels by 5% every week—suddenly dropping RH may stress your plants out or cause shock. Here's the best cannabis growing temperature and humidity when vegging:

 

  • Moderate humidity levels: 40–60%
  • Day temperature/lights on: 71–82°F
  • Night temperature/lights off: 64–75°F

 

Ideal temp and humidity for weed growing

 

Flowering period

When flowering begins, it's crucial to stick to the chart for cannabis temp and humidity requirements in your grow room. Be meticulous about checking humidity levels at this stage, as anything over 60% can rapidly deteriorate your crop and affect bud quality. 

 

During flowering, marijuana plants develop an incredibly strong root system to fulfill their water requirements. There's no need for high humidity, and growers usually defoliate, removing excess leaves that typically absorb moisture. 

 

Maintaining the best temperature and humidity for flowering is essential for hindering mold buildup, as this can transfer from crop to crop. During this phase, mold viciously spreads because the greenery doesn’t need excess moisture, and it can cause a variety of conditions affecting the flowers.

 

Here's the temp and humidity for weed plants during the flowering stage:

 

  • Low humidity: 40–50%—never allow humidity levels above 60% 
  • Temperatures: 68–79 °F 

 

Late flowering (1-2 weeks before harvest)

Up till now, followed a grow room temp and humidity chart and maintained a comfortable environment to prevent your flora from stressing out. When crops near the end of flowering, a little stress is good. Bringing down humidity levels forces plants to produce more sticky resin to protect themselves, giving you more potent buds. 

 

Aside from trichome production, lowering humidity hinders the formation of mold and mildew and deters fungal infections from affecting greenery. Preventing bud rot is the number one reason for decreasing RH during flowering. 

 

High humidity during flowering, especially in the later stages, disfigures the appearance of the buds and reduces their aromatic profile. Stick to these temperature requirements for the healthiest buds possible: 

 

  • Low humidity: 30–40% 
  • Day temperature/lights on: 64–75°F 
  • Night temperature/lights off: 60–68°F 

 

As a summary of all growth stages, here's our handy chart for cannabis temp and humidity: 

 

 

Plant Phase:

Humidity levels (RH): 

Temperature day:

Temperature night:

Seedlings

65–70%

77°F

70°F

Vegetative 

40–60%

71–82°F

64–75°F

Early flowering

40–50%

68–79 °F 

68–79 °F 

Late flowering

30–40%

64–75°F

60–68°F

 

Adjusting humidity levels and temperature

Following a cannabis temp and humidity chart to meet the ideal levels is essential—too much RH leads to diseases and fluid buildup. Too low humidity levels stress crops out, cause necrosis, or reduce bud quality.