Temperatures and Medical Cannabis Growing: From Seedling to Harvest The marijuana industry created an estimated $34 billion economic impact in 2018. Legal sales of marijuana are expected to 12/12 from seed has a big problem. Learn about a better alternative called "Sea of Green" that gives you bigger yields in the same amount of time! How long does it take to grow marijuana? Fr om day 1 of your marijuana plant’s life to a smokable harvest, you’re looking at 2-6 months. Many factors affect the total time (especially the strain
Temperatures and Medical Cannabis Growing: From Seedling to Harvest
The marijuana industry created an estimated $34 billion economic impact in 2018. Legal sales of marijuana are expected to increase from $10 billion in 2018 to $20 billion by 2022, according to the Marijuana Business Fact Book. This means that more and more legal growers (under strict governmental regulations) will be on the American horizon seeking the best indoor growing practices. Temperature and humidity monitoring are essential for growing healthy cannabis plants throughout the entire life of the plant…seedling to harvest.
What’s the Difference Between Temperatures and Humidity Levels?
Temperature and humidity levels interact and are very similar and are closely related to one another. Humidity is the measure of how much humidity is actually being held in the air. Relative humidity (RH) which is one way to measure humidity levels, is how much water is in the air compared to the maximum amount of water that can be held in the air at that temperature. The premise is that warm air holds more water vapor than cold air so it is important to get the warmest air in the environment. It is necessary to extract the warmest air from the growing environment while allowing cool air to enter. The warm air alone has way too much vapor for ideal growing conditions.
Horticulturalists know that the key to success in any growing plant is understanding the lifecycle of the plant. This is also true with growing cannabis. Throughout every stage of growth, cannabis plants will have a constant need for water which the amounts will fluctuate with the humidity. When the humidity is high, plants use their leaves to absorb moisture from the air which results in less water drawn from their roots. On the other hand, when the humidity is low, cannabis plants will take more water through their roots.
Monitoring and having the right humidity encourages strong, healthy, nutrient-dense leafy plants with optimal growth.
Humidity levels must be monitored to prevent:
1. Bud Mold/Rot: A condition when the inside of the plant is taken over by mold. When this happens the buds are unusable.
2. White Powder Mildew: White Powder Mildew (WPM) is a rapidly reproducing fungal disease resulting in a white powder or mildew covering the plant. If caught early enough, it can be prevented, if not the plant will become unusable.
3. Nutrient Problems: If a cannabis plant takes in too many nutrients at once the leaves will turn yellow and the tips will look burnt, called nutrient burn or nute burn.
4. Slowed Growth: If humidity levels are not optimal for the growth stage, they don’t grow as fast as they could. Younger cannabis plants grow better in higher humidity than more mature plants.
So, the next question is how do you measure the ideal levels?
Cannabis Temperature Monitoring In All Stages of Growth
There are four stages or periods of cannabis growing, all requiring different temperature and humidity levels. They are seedling, vegetation, flowering, and late flowering. Experts recommend monitoring levels throughout all four stages using a digital thermometer and a digital hygrometer that include a memory feature so history can be reviewed. The four stages and what they require are:
1. Seedling Stage: Seedlings or clones, little cut-off pieces from a parent plant that needs to develop roots, require high humidity levels between 65 and 70 percent. These high humidity levels are needed because the root system is not established and humidity allows water intake through the plants’ leaves. Young growing cannabis plants prefer temperatures between 75 and 80 degrees Fahrenheit. Anything above 80 degrees Fahrenheit is not recommended.
2. Vegetation Period: This is the stage that cannabis starts developing its renowned leaf shape. It is important to note that light exposure is a very important part of this stage. The number of humidity levels should be lowered by five percent each week throughout the vegetation period. The temperature can be increased, too because roots absorb more water and evaporate through the plants’ leaves. Humidity levels should be before 40 and 70 percent. If wet spots are forming on the leaves, humidity levels are too high.
3. Flowering Plants: The humidity levels of cannabis plants at the beginning of the flowering stage should be lowered to 40 to 50 percent. At this stage, the plants have created a robust root system to meet their water needs. They still absorb water through the leaves. A lower humidity level is required to prevent mold and mildew from forming. Note that mold and mildew infect the plant from the inside the buds, so it isn’t visible at first.
4. Late Flowering Period: This period lasts anywhere between six and 12 weeks and when plants mature. During this time careful temperature and humidity monitoring are necessary. It is recommended that humidity levels be lowered between 30 and 40 percent to improve the yield, flavor, and appearance of the plant. Temperatures can range between 70 and 80 degrees Fahrenheit.
Tips To Adjust Temperature and Humidity for Cannabis Growing
It can be difficult to keep humidity and temperature levels at the right balance throughout the plants’ life cycle. Keep in mind that warm air retains more water than cold air and that relative humidity and temperature interact to create the perfect balance. The following are hands-on tips for adjusting these levels but note that there is technology available in the SaaS Cloud that will wirelessly do the work for you.
Tips to Lower Humidity and Temperature:
- Increase fresh, cool air in the growing area
- Water plants right when lights are turned on in the growing area
- Add a dehumidifier to regulate humidity in the growing area
Tips to Increase Humidity and Temperature
- Keep the soil surface moist
- Surround the room with moist towels and open containers of water
- Use a humidifier to constantly add moisture to the room
It is difficult to be present for the entire life cycle of a cannabis plant. There are more innovative and technological methods for monitoring temperature and humidity levels. Contact SensoScientific for a free trial and to learn more about the most advanced wireless monitoring solution available for cannabis temperature monitoring.
Is 12-12 From Seed Worth It?
Will the “12/12 from seed” cannabis growing technique give you huge yields? In a word, no… but there are benefits to initiating the flowering stage as soon as possible. Giving a 12/12 light schedule from seed germination is a great way to create tiny “bud stick” cannabis plants, which may be perfect for a small stealthy marijuana garden. When modified slightly, the same basic technique can create bigger plants and bigger yields while adding little to no extra time before harvest. And then there is the matter of genetics. Certain strains give better results than others.
The “12 /12 from seed” technique aims to initiate the flowering stage immediately after germination. Learn about cannabis light schedules.
This creates small “bud stick” plants that are typically ready to harvest in 3-4 months. Check out this beautiful example of “12/12 from seed” by Fuel.
If you haven’t heard this term before, “12/12 from seed” means giving your cannabis seedling 12 hours of light and 12 hours of dark each day from the moment of germination. Providing a 12/12 light schedule initiates the flowering stage and causes cannabis plants to start making buds. The idea of this technique is to get seedlings to start flowering as quickly as possible to reduce the time to harvest. Once a plant has started flowering, most strains are ready to harvest within 12 weeks. The sooner you get a plant to start flowering, the sooner you get to harvest.
There’s just one major problem… 12/12 from seed often causes stunted growth and small yields. This results in yields that are often less than 1 ounce per plant, even under strong grow lights.
This seedling took nearly 4 months from seed to harvest under about 150W of fluorescent lights and yielded only 1/2 of an ounce.
I think it looks kind of cool, but 1/2 ounces is not a great harvest after waiting so long. I’ve found you can tweak the light schedule to double or triple your total yield per plant without necessarily increasing time-to-harvest or plant height. More on that below!
12/12 from Seed – What You Need to Know
Something that’s a bit confusing about 12/12 from seed is it seems like seedlings should start flowering immediately. They don’t. I’ve found that photoperiod seedlings won’t start flowering until they’re 3-4 weeks old no matter the light schedule. That means your harvest won’t come any sooner if you initiate 12/12 before seedlings are 3 weeks old. When you give the plant 3-4 weeks of 18+ hours a day, THEN switch to 12/12, you often get better results because plants are quite bigger when buds start forming, without adding much (if any) time to harvest.
Most seedlings won’t make buds until they’re at least 3 weeks old from germination. There’s nothing you could do to get this little seedling to start flowering.
You often get better yields by giving plants 18+ hours of light a day for the first 3-4 weeks. These plants got 18/6 until they reached this size.
I started the 12/12 light schedule right after the above picture. They ended up yielding a lot more than my plants that were given 12/12 from seed in the same setup. Yet they didn’t get much taller or take longer to harvest.
Here are those same plants a month later after they started making buds (plants double or triple in height after the switch to 12/12, especially young plants)
A few weeks of extra light, in the beginning, seems to achieve plants with longer and fatter buds (why was this plant defoliated?)
Plants reward you for giving them a little more time to grow. For example, a solid 4 weeks of 18/6 before 12/12 creates plants that are ready to harvest around the same time as a plant given 12/12 from seed (3-4 months, depending on the strain), but significantly bigger yields.
If you’re worried about plants getting too big, you can gain complete control of plant shape by topping and bending plants to stay flat when they’re young. This increases the amount of bud produced without raising the overall height.
Many people who give 12/12 from seed have chosen this technique to ensure plants stay as small as possible. That’s why it’s common to see these plants in very small pots (like solo cups). Just like with bonsai trees, restricting root space is an effective way to reduce overall plant size. Plants kept in solo cups rarely get bigger than one long bud stick, especially when given 12/12 from seed.
Restricting root size reduces plant size dramatically, especially when combined with 12/12 from seed. Look how big this plant is in relation to the lighter!
12/12 From Clone – When You Want TINY Plants
If you want to grow the absolute smallest plant possible, “12/12 from clone” may be a better choice than 12/12 from seed. A clone is a piece of a bigger plant that was removed and forced to grow roots. Since a clone is technically the same “age” as its mother plant, it’s pretty much a mini mature plant as opposed to a seedling. Because they’re already mature, clones start flowering almost immediately after getting 12/12. That can result in some REALLY small plants at harvest.
Unlike seedlings, clones will start flowering almost immediately after getting 12/12. If you start with small clones in miniature pots, you end up with short buds on sticks at harvest.
These “12/12 from clone” plants are cute and fun! Though not necessarily the most productive when it comes to actual yields.
Auto-Flowering Strains – When Time is of the Essence
Some growers want to use 12/12 from seed to get to harvest as soon as possible, but it’s not actually the best option for a quick harvest. If you’d like to be able to harvest plants even sooner than 3 months, consider giving autoflowering plants a try. Most autoflowering strains are ready to harvest just 2-3 months from germination. That’s less time than almost any photoperiod plant will take, no matter what light schedule you provide. Even better, autoflowering plants on average yield 1-2 ounces each (more if you care for them well), which is better yields than most “12/12 from seed” plants.
The “modern” version of 12/12 from seed is simply using an autoflowering strain. They don’t need special light schedules and are ready to harvest in just 2-3 months from germination.
Autoflowering plants are typically given 18-24 hours of light a day their whole life, which allows them to get bigger in less time than plants under a 12/12 schedule.
Auto-flowering strains are ready in 2-3 months from seed, and yield an average of 1-2 ounces/plant. You can yield even more with low stress training (LST) and great care.
Use “Sea of Green” (SoG) to Maximize Photoperiod Yields
If you want to grow photoperiod strains (or can’t get your hands on autoflowering seeds) but still want to produce big yields as fast as possible, the “Sea of Green” grow style may be a good option. Sea of Green is simply the idea of growing many small plants instead of just a few bigger plants. It works great for photoperiod strains to produce a quick harvest and great yields. It’s kind of halfway between “12/12 from seed” and a typical grow.
For this grow style, growers usually switch to 12/12 when plants are 4-6 weeks old. Since adding a little extra time to the vegetative stage often increases yields, you need to find a balance between getting to harvest as quickly as possible versus harvesting the biggest yields.
For SoG, wait to switch to 12/12 until plants are about this size or a little bigger (note: young plants like this can and will double or triple in height after the switch to 12/12)
SoG in Action – Make sure to fill the entire space under the grow light with plants and you will get a sea of buds!
How long does it take to grow marijuana?
Fr om day 1 of your marijuana plant’s life to a smokable harvest, you’re looking at 2-6 months. Many factors affect the total time (especially the strain and size of the plant) but the average grow takes 3-4 months .
The average indoor cannabis grow takes 3-4 months from seed to harvest. The full range is 2-6 months and depends on the strain and desired size of plants.
You can control the timing if you plan ahead.
2-3 months from seed to harvest
- Use an autoflowering strain (ready to harvest in as little as 10 weeks from germination)
- Standard (photoperiod) plants from seed typically won’t be ready to harvest in under 3 months
- Average 1-2 oz per plant
- In 5-gallon pots with strong grow light, expect up to 4 or 5 oz per plant indoors
- Autoflowering plants can get huge outdoors in full sunlight, where they can produce many ounces per plant
3-5+ months from seed to harvest
- Photoperiod strains are your best bet (they are flexible on timing and allow you to choose the final plant size/yields)
- In 5-gallon pots with strong grow light, expect up to 5 oz per plant indoors
- Up to 10 oz per plant or more if you have a strong light, a 10-gallon pot, and let the plant get big before initiating the flowering stage
- When growing photoperiod plants outside, you must get a strain that’s suitable for your climate and plant in the spring so buds are ready to harvest before winter
These factors have the greatest impact on total time from seed to harvest:
- Cannabis strain – Some strains are ready to harvest in under 2 months, while others may need 5 months or more from seed to weed. Strain has a big impact on growing time. Luckily, breeders almost always give time estimates so you can plan ahead.
- Desired yields – Do you want to grow a few grams, a few ounces, or a few pounds? Bigger plants produce bigger yields, but also need more time to grow.
- Setup – Different grow methods or setups can add or subtract a few weeks. For example, plants grown without added nutrients tend to grow slower than plants getting nutrients in the water.
How to grow marijuana as quickly as possible:
You want to get an auto-flowering strain. These cannabis plants automatically start making buds after about a month from germination, and are ready to harvest by the time they’re 2 or 3 months old.
Auto-flowering plants tend to stay small since they go from seed to harvest in under 3 months. These auto-flowering plants produced about 7 ounces.
However, if you take really good care of auto-flowering plants for the first 4 weeks and give a lot of light, they can grow much bigger. These auto-flowering plants reached half this height in the first 4 weeks and produced about 11 oz under the same grow light as above.
Counter-clockwise from top left: Alaskan Purple Auto, White Widow Max Auto, Candy Kush Auto, Pink Kush CBD 30:1 (short purple plant), Zkittlez Auto, Gelato Auto
Here are some of great auto-flowering strains I’ve personally grown and recommend. These are all ready to harvest 8-10 weeks from germination:
(American stabilized version) – These plants responded well to plant training and produced nice yields. I really enjoyed the strong yet unique bud effects of this strain. It reminded me of a sativa/haze with more of a body stone. – Easy to grow with buds that smell amazing. This didn’t get the best yields, but the bud quality was worth it. by G13 Labs – An extremely popular autoflowering strain. Plants stay short, are quick-to-harvest even for an auto, and the sparkle-encrusted buds smell like heaven. by Bomb Seeds – I’ve grown 5 different plants of this strain over multiple grows in different setups, and every one came out marvelous. Easy to grow, great yields, beautiful sparkly buds, and potent effects. Highly recommended! by Dutch Passion – Average potency buds, but the best yields of any auto-flowering plant I’ve ever grown. Always yields twice as much as the next auto-flowering plant in the tent. However, plants can get big so watch the height! A great choice for someone who wants classic bud effects that aren’t too overwhelming. by MSNL – The plants grew big but with a good bushy structure (not too stretchy), responded well to training, and produced enormous yields of high-quality bud. (American stabilized version) – This strain has grown fast and healthy for me and produced fat buds that smell sweet and look gorgeous.
Recommended Autoflowering Breeders
Many other breeders also produce great auto-flowering strains (Dutch Passion, FastBuds, Barney’s Farm, etc.), but the following breeders stand out for consistency.
Zkittlez Auto is ready to harvest 8-10 weeks from germination. Every time I grow this strain the smell and bud effects are excellent
What if time is not an issue?
This gives you the freedom to choose the exact strain you want without any worry about how long it will take. This gives you the freedom to grow some strains that otherwise are inaccessible to growers who are worried about timeframes.
Strains from warm climates tend to have long flowering periods before their buds are ready to harvest, adding weeks or months to the time needed. Long-flowering strains often produce higher yields than short-flowering strains because buds have more time to grow. For example, Acapulco Gold takes almost 3 months after initiating 12/12 before buds are ready to harvest. However, it produces amazing yields and unique psychedelic effects.
Important Milestones in the Marijuana Plant’s Life
Depending on how you set up your grow, it can take anywhere from 2 months to 6 months or more to grow a marijuana plant from a seedling to the point where the plant is ready to harvest. Some methods, such as growing hydroponically indoors, give your flexibility to get a harvested plant in as little as 2-3 months. Growing outdoors generally takes longer than growing indoors and is more dependent on when you plant your seeds and how long your growing season is.
Once your plant is harvested, there is a drying and curing process that takes about a minimum of two weeks before your buds are “ready” for smoking. If you aren’t a smoker and plan on turning plants into edibles or concentrates, you should still dry your buds but typically you don’t need to cure your buds.
For more information about how to grow your own marijuana at home, then check out my Basic Marijuana Growing Guide or one of my more detailed How-To Guides which will explain how to grow your marijuana plant from beginning to end.