Cannabis seeds need only water, heat, and air to break dormancy and germinate; they do not need extra hormones, fertilizers, or additives. Seeds sprout Climate is key to cannabis growing. In this post we analyse the importance of relative air humidity at every growing stage. We’ll define the ideal hygrometric level … How to measure and adjust humidity levels in your marijuana grow room? A guide with a schedule for the best humidity levels for your grow.
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.
What is the optimum humidity level for each stage of cannabis growing?
In order to start growing in the best possible conditions, it is adamant to understand the meaning of this technical term. Relative air humidity levels give us information on the concentration of water vapour in the air.
It is important to realise that air humidity is closely connected to air temperature, as hot air is more humid than cold air.
That’s why an air conditioning unit dehumidifies and cools the air at the same time.
When air humidity levels come close to 100%, the air is not capable of retaining the excess moisture, which leads to condensation in the shape of small droplets of fog, morning dew, or rain.
For instance, if the temperature of your grow space is 30ºC, with a relative humidity of around 33-35%, and the temperature suddenly plummets to 10-12ºC, the humidity level can quickly reach 100%.
This can become a critical situation at the end of the flowering period if the ‘dew point‘ is reached. This is a parameter that reflects the cannabis flowers’ humidity level. Bad management of the relative humidity levels of your grow space, caused by abrupt temperature variations, could lead to the appearance of mould in your buds.
Air circulation for cannabis growing
So what is the most favourable humidity level for each growing stage?
Here we show you the ideal humidity levels for every growing phase of your cannabis grow.
Germination / beginning of the cuttings’ rooting period
It is really important to maintain a relative humidity of 80-90% in your mini greenhouse during this phase. This applies to seeds that have just sprouted and also to young seedlings (0-10 days old). These still don’t have a strong radicular system and are therefore pretty fragile.
They require high moisture levels so they can concentrate all their resources on the development of a strong and vigorous root mass. The correct day temperature should be 25-26ºC, and 21-22ºC at night.
Young seedlings and 10-day-old clones
At this point, the required hygrometric conditions should range between 70 and 80%, with similar temperatures to those in the initial stage.
The moisture level for this phase needs to be quite high as the root mass is not very vigorous and actually non-existant in the case of the young seedlings. That’s why it’s necessary to point all technical parameters towards this objective.
It is essential to maintain the correct relative humidity as cuttings will start to develop their first roots between 12 and 20 days after having been planted in the growing medium. This is a crucial point for the appropriate evolution of these young plants.
At this stage the young seedlings, derived from seeds or cuttings, will have developed a radicular mass that is significant enough for them to feed through and therefore reach their maximum potential before being transplanted to a new pot for further development.
Establishing new climate conditions at this stage is vital as the aim is to achieve a reasonably high humidity level, but slightly lower than at the beginning. A good balance should range between 60 and 70%.
Temperatures must be kept between 22-28ºC during the day and 18-22ºC at night. These conditions guarantee the plants’ well-being and facilitate good metabolic function, as well as overall optimum development.
At this point, the radicular system is strong enough for the plant to absorb a higher amount of nutrients and develop a much more resistant immune system.
At the start of the flowering period, when the ‘stretching’ or the final growth boost occurs, plants need specific climate conditions for this transitional phase.
As this is still a transition period in which plants progressively end the veg phase, the humidity level needs to be set at 50-60%. It is also essential that the temperature remains between 20-26ºC both day and night.
This prevents thermal shock and guarantees that plants will be ready to produce those delicious flowers. It is vital that their well-being is taken care of so they can concentrate all their resources on their final objective: quality and quantity. These measures are valid for the first 3 to 4 weeks of flowering, depending on the strain.
In the second part of the flowering phase the humidity level must be reduced to 40-50%. In the two to three final weeks it’s preferable for this figure to be closer to 40%.
This is absolutely essential, particularly if you’re growing strains that are sensitive to mould or that produce dense flowers.
If you follow our guidelines, chances of botrytis hitting your flowers will be slim. As far as temperature goes, we advise you to stick to 18-24ºC during the day and 17-20ºC at night.
This way you’ll be able to control your flowers’ dew point, which is crucial in order to prevent fungi and avoid ruining all your hard work.
Brian Worms After completing my studies in International Trade and Marketing in France, I’m more interested in the world of communication today. Blogger, grower and real cannabis toker for more than 20 years, always looking into the rarest and finest cannabis genetics. My passion for cannabis is so deep that it’s become something of a lifestyle now… My work is like a dream come true.
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We are going to take some time to delve into some much-needed information to further your understanding of the importance of humidity for seedlings when growing marijuana plants.
What is humidity
Humidity is expressed as the quantity of water vapor in the air. Humidity plays a necessary role in influencing how much evaporation occurs in cannabis plants.
Your plant will take in more nutrition and water when the humidity is low.
If for any reason the evaporation strain gets to be too much, marijuana plants will guard themselves against scarcity by closing their stomata. So naturally, this will stunt the growth of your plant due to the lack of water absorption.
This is why you must have the proper humidity levels in your marijuana factory. When the plant is in the growth stage, it will need high humidity, unlike the blooming phase.
This is mainly because the roots of baby plants are much smaller. Measure the humidity using a hygrometer. In the first stages of growing your plant, the humidity can be about 70%, and you can reduce it by 5 every week until it gets to 40%. Included in this article is a helpful schedule to assist you with the right information on humidity levels for both indoor and outdoor growing.
Relation to temperature
Before we go any further, we have to discuss the connection between temperature and humidity. First you must understand that the percentage of absorbable water is determined by the temperature. At the temperature of 68 degrees Fahrenheit, air can take in up to 7.2 ml of water. In this case, air has a corresponding humidity of 100%.
With temperatures and humidity such as that you are guaranteed to see absolutely nothing because the water vapor is very high. At 32 degrees Fahrenheit, the air will take in around 5 ml of water. For this reason, air is much drier during the winter time than the summer months.
‘The hotter it is, the more moisture the air could hold at the same temperature.’
Since you will be airing out your grow room quite frequently, you will end up releasing the humidity as well. So you have to be sure that your marijuana factory is always moist so the humidity level goes up. Later in the article you will be informed of options for adjusting the humidity levels.
At first, your marijuana cuttings will have very small roots so they are not able to take in much water yet. At this stage, you want them to evaporate a very small amount of water. Cutting will only evaporate a small amount of water when the humidity is high, and require fewer roots.
Another way to reduce the amount of evaporation is chopping the bigger leaves halfway from the cutting. A humidity of 70% is exactly what you want when putting the cuttings in your marijuana factory.
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Your cuttings will begin growing roots in a clone box when the temperature is around 71.5 degrees
Fahrenheit in a very humid environment and fluorescent lighting.
I suggest the cuttings go beneath a 600-watt HPS lamp in an environment with 30% humidity for good results.
For as long as the 2 nd or 3 rd week of blooming the roots are going to grow the size of the actual plant. The roots must be durable for proper water and nutrient absorption.
If you’ve produced a bountiful harvest with your desired attributes, cloning these marijuana plants is the next best thing to do so you can recreate the same results.
Seedlings require a separate set of rules since they have a taproot at germination that takes in moisture and grows fairly quickly. Never clip the leaves of a seedling. The leaves are necessary for absorbing light and evaporating water.
To help the seedlings take in water and nutrition through its leaves, have the humidity at high levels. Begin at 60% and slowly work your way down to 40%. Click this link to buy marijuana seeds
As your plant start flowering, you can gradually decrease the humidity level.
At this stage the roots are very mature, so the plant is able to take in the most nutrients and water. You will want to reduce the humidity level in the flowering stage since mold has a tendency to flourish in high humidity environments.
With age, there is a higher chance of your marijuana plant getting mold.
As a result of the high humidity, water gathers around the tops and that when mold has the opportunity to develop. Bud rot is the most frequent type of mold.
Levels of humidity in cannabis plants
Once the plant is fully grown you will need to start thinking about harvest time. Our free little Harvest Guide will help you determine the best moment to cut your plants.
Follow this schedule to ensure you give your plants the right amount of humidity for optimum growth. Notice there is a difference in clones and seedlings.
Clones humidity level
|Growth Week 1||70%|
|Growth Week 2||70%|
|Flowering Week 1||65%|
|Flowering Week 2||60%|
|Flowering Week 3||55%|
|Flowering Week 4||50%|
|Flowering Week 5||50%|
|Flowering Week 6||45%|
|Flowering Week 7||45%|
|Flowering Week 8||40%|
|Flowering Week 9||40%|
Check this complete Marijuana Grow Schedule with temperatures, humidity, watering and nutrients tips.
Seedlings humidity level
|Growth Week 1||60%|
|Growth Week 2||60%|
|Flowering Week 1||55%|
|Flowering Week 2||50%|
|Flowering Week 3||50%|
|Flowering Week 4||50%|
|Flowering Week 5||50%|
|Flowering Week 6||45%|
|Flowering Week 7||45%|
|Flowering Week 8||40%|
|Flowering Week 9||40%|
How to raise the humidity in your grow room
So, you have a few options for raising the humidity in your grow room. For starters, you can try spraying water on the walls and flower.
Also, try putting the lights further up so the temperature will go down a little near the plants. This way you won’t have to turn on the extractor fan as often. If you put bottles or buckets of water around the grow room, or even wet towels, this will raise the humidity level.
How to decrease the humidity
Dehumidifiers are most certainly your best option. It has the capability of taking moisture from the air and draining it or holding it in a reservoir. Make sure to get a larger humidifier because the smaller ones fill up quickly.
Once your marijuana plant starts flowering the humidity will need to be decreased, so it is necessary to dehumidify. Try using the extractor fan on a higher setting than usual or even you can even shoot cold air into the room.
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Keep in mind that the humidity outside may influence the humidity in your marijuana factory. For instance, if on a rainy day the humidity increases quickly, you can shut off the extractor fan or turn it to a much lower setting. Make sure the temperature doesn’t rise too quickly because you’re getting less cold air from outside.
How to measure humidity levels
Hygrometers are used to measure humidity levels (wiki on hygrometer at this link). All you have to do is put it over the plants, so long as it is in an area that easily aired out. The analog hygrometers cost $5 and you can buy a digital one for $10.
The higher priced hygrometers are usually of better quality. For ease of use, get the one that has a wire attached to it. This makes it easier to see the humidity without having to turn the lights on in the room. These devices have a built-in storage bank that tracks the highest and lowest values, to help you determine how well you stayed within the preferred range. Buy the best hygrometers at this link.
Watering your plants causes the humidity to go up quite a bit, which is fine when in the growth stage because you just spray the floor and walls to raise the humidity. During the flowering stage, humidity levels often go up way too much after you water your plants.
Once the lights are no longer on in the grow room, the temperature decreases and extracting a lot of hot air is unnecessary, which usually is the cause of humidity increases.
Nourish your plant with water once the lights are on, that way they will evaporate most of the water throughout the day. Understand that spraying water on top of the buds is pointless because you will raise the possibilities of the humidity rising and leading to mold.
Humidity is much less of an issue when growing your cannabis plants outdoors. The springtime and the start of summer offer higher humidity which works just fine since there are no buds present on the plant for moisture to gather. Any moisture on the plant from morning dew will easily evaporate throughout the day.
Once Summertime ends, the flowering stage starts and there is a shift in the climate, resulting in cooler days and more rainfall. This usually makes the humidity higher. In the cooler months, the morning dew could be an issue since the sun is not guaranteed to come out and the temperatures are sometimes too low to evaporate it.
Luckily a tad bit of rain will not cause the buds to rot, but just in case you may want to be on the lookout for this. In the last of the blooming stage, it might be a good idea to brush the dew off your marijuana plants in the mornings. If you notice that rain is expected, go ahead on move your plants to a location where they will be kept dry, away from the rain. It is always best to take the necessary precautions.
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