So what is the best temperature for growing weed and what about the humidity in your grow room? Check it out! Cannabis seeds need only water, heat, and air to break dormancy and germinate; they do not need extra hormones, fertilizers, or additives. Seeds sprout 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
Best Temperature and Humidity for Growing Weed
Getting the temperature right for your cannabis plants is an essential part of each stage of the growing process. If the temperature in your grow room or outdoors is too hot or too cold, your young weed plants will not be able to photosynthesise properly, and this will inevitably affect their growth and development. However, it is not as simple as saying ‘this is the correct temperature; the temperature needs of the plants vary according to their stage of development, so you must have some knowledge of their requirements. To help you, we have written this guide which will explain the best temperature and humidity for growing weed for each phase of your young weed plants.
Now, we understand that establishing the ideal temperature for weed plants can be tricky – some say that it is as much instinct as it is science. However, it is certainly possible to work things out for the growing conditions of your plants, and this article will tell you everything you need to know.
What you need to know about temperature and humidity
The first thing you need to understand is the close relationship between temperature and humidity levels. Let’s look at science. Humidity refers to the amount of water vapour present in the air. At higher temperatures, molecules move at top speeds; thus the probability of condensation of water vapour due to the collision of molecules is less. This makes the air hold more water vapour at high temperatures. In other words, as the temperature increases, the humidity of air also increases.
Most plants including cannabis plants, need humid air to thrive. This is because the pores through which they breathe lose most of their moisture when the surrounding air is dry, a loss that the plant can’t always replace through the water absorbed by its roots. The thinner the leaf – and cannabis plants have quite small, narrow leaves, the higher its need for humidity.
When deciding the correct temperature for your plants, therefore, it is also sensible to assess the humidity levels as the two go hand-in-hand. To do this, you should invest in a good-quality thermometer and a hygrometer, ideally digital models with the ability to store historical maximum and minimum levels.
When the temperature is 68°F (20°C), air can absorb 7.2 ml of water maximum. When this occurs, the air has a relative humidity of 100 percent. There will be so much water vapour that the air will be as dense as a cloud and will affect your ability to see anything. Air with a temperature of 32°F (0°C) is only able to absorb about 5 ml of water. This is the reason why the air is a lot drier in the winter than in the summer.
Temperature and humidity for the germination phase
The first moments of your cannabis plant’s life are crucial. Germinating seeds indoors will allow you to have more control over the temperature, but it is also possible to do so outdoors if the climate conditions allow. Having a high temperature (from 22 to 26°C) is an important factor for your seeds to decide to emerge into the world.
However, the temperature must not fall to less than 20 degrees Celsius nor rise to more than 30. If you are using a greenhouse for the germination phase, be warned that it can get sweltering so you must regularly monitor the temperature. Humidity must also be continuously monitored. If the seed trays dry up, germination will not take place or recently sprouted shoots will wither and die. You must not forget to add water when necessary – a spray dispenser is gentle for this, but you should not give them too much water. The seeds should only be soaking wet during the first two days.
Once the first seedlings emerge with two cotyledons (the first two round leaves that develop), they should be carefully transplanted. If the seeds are autoflowering, you should transplant them to a large pot. If they are feminised seeds, however, you can transplant them to a smaller container and move them to the large bowl when they are a bit more established.
Best temperatures and humidity for the seedling phase
The optimal conditions for cannabis seedlings are a sunny, warm (20-25ºC) and humid environment with well-circulated air. Their underdeveloped root systems mean that seedlings need to be exposed to lots of light and heat. Problems arise as their immaturity means that they cannot withstand high temperatures. Therefore, we recommend that growers maintain 20ºC to 25ºC indoor environments when the lights are on.
Humidity levels also need to be high. Levels between 65 percent and 70 percent are sufficient for seedlings to absorb enough water through their leaves.
Optimal temperatures for the vegetative phase
You can start to relax a bit during the vegetative phase. As cannabis plants mature, they grow stronger and better able to cope with extremes of heat. They start to be more resistant to heat and cold. You can raise the temperature to as much as 30ºC.
As the roots have sufficiently developed to absorb plenty of water, you may wish to reduce humidity levels by 5 percent each week. The relative humidity should ideally fall between 40 percent and 70 percent.
The best humidity and temperatures for the flowering phase
The last phase of the cannabis growth cycle is the flowering phase. Growers should aim to maintain warm temperatures that are pretty much the same as when the plants were at the seedling stage. Ensure that the temperature stays at a nice warm 20ºC to 25C to prevent buds from burning their terpenes. This will allow your plants to produce deliciously potent flowers.
It is also a good idea to lower humidity levels to about 40 percent to 50 percent, especially during the late flowering phase. This encourages the production of highly-prized resin and a higher terpene content leading to a more aromatic and flavourful crop.
Cultivators should be advised that typical temperature variance when the lights are switched off is 5ºC, and this applies to all the phases of development.
Temperatures that are too cold
Temperatures that are too cold will slow down a cannabis plant’s metabolism and its roots system will become increasingly ineffective. If temperatures drop below 12 degrees, the plant is even at risk of death.
The obvious solution to boosting the temperature of the grow room is to get an electric heater and plug it in. This has several disadvantages, however, mainly due to its high consumption of electricity but also because of its drying nature which can affect levels of humidity, and the direct distribution of the heat which makes it hard for all the plants to enjoy the uneven heat. An oil-filled portable radiator is another option if you can get one which isn’t too large to fit into the grow space. We recommend small tubular electric heaters which can be placed conveniently on the floor and only use a few watts of electricity. Radiating cables for indoor use are another excellent alternative, especially if you need to heat trays of seedlings.
Temperatures that are too hot
Reducing heat levels in a grow tent can be much harder to control than the reverse. We recommend using electric fans to circulate the air as much as possible to disperse the heat and thus cool the young cannabis plants.
Placing an exhaust fan in the ceiling vent of your grow tent is also highly effective at reducing heat. After all, heat always rises to the top.
You could also use a cooling humidifier which reduces temperatures while boosting humidity levels. Just take care that the humidity does not increase too much for the growth phase. Remember, seedlings need higher levels of humidity than vegetative marijuana plants, for which 40 percent is optimal.
Jorge’s Cannabis Encyclopedia: Seed Germination
Cannabis seeds need only water, heat, and air to break dormancy and germinate; they do not need extra hormones, fertilizers, or additives. Seeds sprout without light in a range of temperatures. Strong, viable, properly nurtured seeds germinate in 2 to 7 days. At germination, the outside protective shell of the seed splits, and a tiny, white sprout (radicle) pops out. This sprout is the root, or taproot. Cotyledon, or seed, leaves emerge on a stem from within the shell as they push upward in search of light.
Break dormancy: Put newly harvested seeds in the refrigerator for a week or two to simulate winter. Remove and germinate. Seeds will germinate more uniformly because they all come out of dormancy at the same time.
Timeline for Germinating Most Seeds:
At 36 to 96 hours – Water is absorbed, root tip (radicle) pops through outer shell and is visible.
At 10 to 14 days – First roots and root hairs become visible.
At 21 to 30 days – At least half of seeds are rooted by day 21. Seeds not rooted by day 30 will probably grow slowly.
Once seeds are rooted, cell growth accelerates; stem, foliage, and roots develop quickly. Seedlings develop into full vegetative growth within 4 to 6 weeks of germination.
Seeds are Prompted to Germinate By:
Water: Soaking seeds in water allows moisture to penetrate the protective seed shell within minutes. Once inside, moisture continues to wick in to activate the dominant hormones. In a few days, hormones activate and send enough signals to pro- duce an initial root tip. The white radicle (rootlet) emerges to bring a new plant into the world. Once a seed is moist, it must receive a constant flow of moisture to transport nutrients, hormones, and water so that it can carry on life processes. Some seeds need lots of moisture to wash out the dormancy hormones in the seed coat, and if they do not get enough moisture, they do not germinate. Conversely, too much water deprives the seed of oxygen, reducing its quality or destroying it. If fragile germinated seeds are allowed to suffer moisture stress now, seedling growth will be stunted. Soaking most seeds in water for 12 to 24 hours is all they need to initiate germination. All the nourishment for a seed’s initial growth requirement is pulled from the fleshy cotyledons, or seed leaves. Water seedlings with low-EC (electrical conductivity) household tap water during the first week or two of life. Supple- mental nutrients are unnecessary and if applied in excess can disrupt internal seed chemistry. Some gardeners prefer to germinate seeds using distilled or purified water that contains virtually no dissolved solids.
Temperature: Overall, cannabis seeds germinate in temperatures from 70°F–90°F (21°C–32°C) and grow best at 78°F (26°C). Temperatures below 70°F (21°C) and above 90°F (32°C) impair germination. Low temperatures delay germination. High temperatures upset seed chemistry causing poor germination. Seeds germinate best under the native conditions and temperature ranges where they were grown.
Air & Oxygen: Sow seeds twice as deep as the width of the seed. For example, 0.125-inch (3 mm) seeds should be planted 0.25 inches (6 mm) deep. Adequate oxygen is un- available for seeds planted too deeply, and tender seedlings have insufficient stored energy to drive through deep layers of soil or crusty hard soil when sprouting.
Agricultural Astrology — Planting by the Moon
Ancient Babylonians and Egyptians planted and harvested based on moon phases in relation to geographic location. The premise is that plants grow better when planted during the appropriate moon phase.
Moon phases cause ocean tides to rise and fall. They also affect the rise and fall of moisture in soil and fluids inside plants. The moon phase influence is said to be the same indoors, outdoors, and in greenhouse-grown cannabis.
Cannabis gardeners who plant by the moon report faster-sprouting seeds that grow into vigorous plants. However, scientific evidence is lacking in regard to cannabis and other plants’ relationship with agricultural astrology.
Seeds need oxygen from the air to germinate. Growing mediums that are too moist (soggy) will cut off oxygen supplies and the seeds will literally drown. Cannabis seeds germinate best when moisture is between 60 and 70 percent.
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.