- Introduction: Prefered Temperature
- Nighttime Temperature
- Controlling The Temperature
- Vegetating Marijuana and Temperature
- Do Vegetating Marijuana Plants Need a Dark Period ? (Night)
- Flowering Marijuana and Temperature
- Clones, Seedlings Marijuana and Temperature
- Conclusion – Indicas & Sativas
Growing organic marijuana does best between 70 and 80 degrees Fahrenheit. I have found that temperature is critical to marijuana in the flowering stage of their life. Temperatures above 80 degrees will cause your plants flowers to elongate, your buds will be less dense and your harvested weight will be low. I have also found that the temperature is not critical during the vegetating stage, however keeping the temperature below 90 degrees is advisable for optimum growth.
Why below 90? When you grow organic medical marijuana outside it’s above 90 degrees a lot of the time. So whats the deal ? The deal is, metabolism of the growing marijuana will slow way down. In nature, the days warm up slowly, peak, then slowly cools down. Where medical marijuana grows best, daytime temperatures are not above 90 degrees for very long. In nature you have a cool spring, a warmer summer, and then it cools down again in the fall. In the fall is when organic medical marijuana flowers naturally. The days have become shorter which triggers flowering and it’s naturally cooler. This is why we want our flowering medical marijuana cooler. We want to emulate the outdoors as best we can for indoor growing. Which is why we want our flowering plants below 80 degrees.
Because we want to emulate the outdoors, we would also like our organic medical marijuana to have a cooler nighttime temperature. This can happen naturally if you have proper ventilation, but you might want to cool your space even more to bring out the natural colors that happen in the later stages of flowering. A temperature swing of no more than 20 degrees is preferable. Organic medical marijuana can survive temperatures as low as freezing with little damage for a short time. The perfect night-time temperature for flowering marijuana is between 60 and 70 degrees F. I have my flower room thermostat set for 65 degrees F at night and it regularly goes to 60*F. The perfect temperature for vegetating organic medical marijuana is 70 to 75 degrees.
To keep your flowering plants below 80 degrees may need some type of air conditioner. In dry climates a swamp cooler
works very well. In humid climates you will need an air conditioner which will also dehumidify your growing space. Dehumidifying in a humid climate is a good thing and maybe a must thing to do, to prevent powdery mildew. With the use of an air conditioner you’re also able to lower your night-time temperature to your desired level.
Marijuana is an annual plant. This means , it sprouts from seed, grows during the warm months of summer, flowers at the end of summer and into the fall when it’s cooler. Then it dies whether it was pollinated and produced seed or not. Annual plants must be grown from seed every year unless cloned. This means vegetating marijuana likes the temperature to be warm. A good rule of thumb is, if the grow room is comfortable to you it’s comfortable for the marijuana plants. If the grow room feels hot or cold to you, the plants feel the heat and chill also. Vegetating marijuana would also prefer cooler nights of at least 10 degrees, if you are running your lights on an 18/6 cycle. If you are running your lights on a 24/0 cycle you want a constant temperature.
Vegetating Temperatures for Optimal Growth : Day 75 – 86 degrees F Night 70 – 75 degrees F (With CO2 80-85 degrees F)
Vegetating Temperature Extremes You Can Get Away With : Day: 86-95 degrees F But almost all growth stops above 90*F, over 100 degrees for short periods is ok with a good brease and humid conditions. Growing in a high humidity environment enables marijuana plants to grow well, in higher temperatures. If you are growing using CO2 you may want to raise your grows temperature to the high end of the temperature range (80-85 degrees F).
The debate goes on ! There are very good debates from the best growers on this subject. And as one would expect, they disagree with one another. Both sides make excellent points, but who is right? The points they disagree on are many, too many in fact for me to discuss here without confusing everybody. But I can tell you what they do agree on. They agree that lights on 24/0 will consume 25% more electricity. They agree that 24/0 will enable your plants to grow up to 33% faster. They agree that no harm will come to your plants under 24 hours of light. They agree that under 24 hours of light you must monitor your temperatures very closely so plants don’t get too hot under the grow lights. Temperatures above 86 degrees F slows down plant growth and as the temperature rises above 86* F growth slows down even more. Too much heat may negate the advantage of running your lights 24/0.
Two Reasons to Go 24/0 ! There are only two reasons to grow under 24 hours of light :
- The plants will grow up to 33% faster. ( This may or may not be a good thing.)
- The plants will grow more compact and dense with more bud sites. ( I read where one fellow was growing under 24/0 for 8 weeks and then switched to 18/6 for the next two weeks. His plants grew much taller in those 18/6 days, and he was convinced his plants grew faster in the 18/6 days.) What his plants really did, was stretch along with growing. With less light the plant stretches (space between nodes gets longer), which can sure appear like “more growth”. The brighter the light and the longer the lights are on the more compact and dense your plants will be. The opposite is also true. The lower the lumens the more your plants will stretch to reach the available light.
Night or No Night ? That is The Question ! Although giving your marijuana plants a rest from photosynthesis is a good thing, it is not necessary. Well then, which is best, giving plants a night or not ? That’s for you to decide ! I say : “Let your grow decide for you.” What do I mean by that ? It’s really a very simple decision.
How fast do you want your vegetating plants to grow? If you want fast production and growth, go with 24/0. This is good if you have an empty flower room and need to fill it up quickly. So, if you are only growing a few plants and have the room to flower them when they are at the proper height for flowering go with 24/0. If you have a perpetual grow or if your flower room is full you may not want your plants to grow that fast. If the plants grow too fast, they may be overgrown and too large for your flower room when your flower room is ready again to accept new plants. You can’t really speed up the flowering time, so you must wait until the room is ready again from the crop that was in there before. This is where timing your crop comes in.
Timing is everything for a perpetual grow ! Your flower room must be ready to accept new plants when the vegetating plants are at a certain height. This dictates how fast you want your plants to grow, or at the very least how you manage your grow. You must time your clones and seeding according to the light schedule you choose. If you choose 18/6 for your lights you will start your vegetating plants sooner than those going with the 24/0 schedule.
Marijuana naturally flowers in the fall when the daylight hours are shorter and the temperatures are cooler. For our flowering organic marijuana we want our grow room to emulate the fall season the best we can. This means cutting our light schedule to a 12/12 and cooling our flowering room down from the temperature we vegetated the plants in. Cooling the flower room down at night will also bring out the natural fall colors of your plants. These cooler temperatures also aid in trichomes production and the aroma of your organic skunk marijuana. For the color change to take place and to bring out the best aroma of your buds, including increased trichomes production you want a temperature swing of at least 10 degrees F between day and night in the flowering stage. The temperature swing should be no more than 20 degrees F.
The optimal day temperature range for flowering marijuana is 70 – 80 degrees F(21.1-26.6 C)(80-85 F with CO2). If the temperature of flowering plants is above 80 degrees F the flower buds elongate and become airy, diminishing the yield and quality of the buds. Trichome productions slows and the aroma of the buds also diminishes. The optimal nighttime temperature for flowering marijuana is 60-65 degrees F. Temperatures above 86 degrees F and below 59.9 degrees F decreases THC potency and slows growth. At 55.5 degrees F the plant undergoes mild stress, although some strains withstand frost temporarily. Frost occurs when air temperatures dip below 32 degrees F(0 °C) and ice crystals form.
Flowering Temperatures for Optimal Growth :
- Day : 70-80 degrees F
- Night : 60-65 degrees F
- There are no acceptable extreme temperatures ranges that are ok for flowering marijuana .
Clones and seedlings like warm temperatures with a high humidity. A warm area with a low humidity will require a longer time for clones to root, and will slow down the seeds ability to sprout. Clones should be rooted between 75 and 85 degrees F day and night. Seeds also should be sprouted between 75 and 85 degrees. A dome over your seedlings and clones will help maintain a higher humidity. This higher humidity enables quicker rooting of the clones and germination of the seeds along with less stress.
- Clones and Seedlings : Day and Night : 75-85 degrees F
Keep in mind that Indicas like the temperature towards the warm side, so the upper range of the temperature scale is good for them. The Sativas like the temperature towards the cool side, meaning the low side of the temperature scale is good for them. This is because Indicas are from tropical areas and Sativas are from semi-tropical to temperate areas of our planet.
Organic marijuana and the temperature your plants are growing in, is extremely important. If the temperature is too high you risk slowing the plant’s growth to a crawl. In the case of clones, temperatures above 90* and the clones may not root at all or take an extra long time to root. The same goes with too cool of a temperature in your grow. In the flower room temperatures above 80 degrees F and your buds will suffer exponentially. On the other hand if the temperature is too cool in the flower room the buds will have poor development and structure. Growing organic marijuana at the proper temperature is advantageous to you and your crop, if you want a good yield and excellent quality.
Go to Page : Marijuana and Humidity !
Author Tom D.