Germinating cannabis seeds is one of the most exciting parts of the whole grow. It is almost magical to summon new life from a dormant seed; however, it can be very frustrating when things don’t go well. In this article, I explain how to germinate cannabis seeds successfully. I begin by reviewing the science of germinating cannabis seeds. I then describe several common cannabis germination strategies and share some cannabis germination tips and tricks. At the end of the article, I provide my step-by-step guide to germinating cannabis seeds.
Germination will always be exciting, but it does not need to be intimidating. There are many ways to germinate cannabis seeds successfully. Understanding the science and the shifting needs of the developing plant will allow you to choose the germination strategy that is right for you.
The Science of Germinating Cannabis Seeds
Cannabis seeds are among the easier seeds to germinate. They are large dicotyledon seeds that store a reasonable amount of energy for early life. Furthermore, cannabis seeds do not have any significant seed dormancy factors to overcome. If they are viable seeds they will germinate easily when exposed to the correct conditions.
Seeds become Sprouts During Germination
This may sound obvious, but it is important to consider because seeds and sprouts are different. When the cannabis seed is still a seed, it is resilient and does not depend on ideal conditions to survive. However, sprouts are different. As soon as the seed cracks open and exposes the radicle (tip of the root) it becomes a sprout. As a sprout, it becomes much more sensitive to external conditions. Whereas the seed only needs warmth and moisture to germinate; the radicle on a sprout needs warmth, moisture, oxygen, and darkness to survive and grow.
Germination Stage 1: Imbibition
The seed’s journey to planthood begins by getting wet which starts the process of imbibition. Imbibition is similar to rehydration. When wet, the testa or seed coat of cannabis seeds imbibe water which causes them to swell and soften. The force of water entering the cells in the testa physically ruptures the seed coat and allows the radicle (root tip) to escape. The imbibition of water also activates the metabolic activity within the seed protoplasm.
Warmth is Required for Metabolic Activity
The metabolic activity within the seed will only activate if the temperature is in the appropriate range. Like other seeds, cannabis seeds will not successfully germinate if the temperature is too low or too high. Room temperature is warm enough to allow germination, but warmer temperatures enable more metabolic activity and faster germination. The ideal temperature range to germinate cannabis seeds is 80-86 F (27-30 C).
Germination Stage 2: Respiration
Seeds carry stored energy to help power metabolic activity and growth until the plant can begin photosynthesis. However, just like humans and other animals, plants must engage in respiration in order to convert that stored energy into active energy that the plant can use. During the earliest stages of metabolic activity as the seed awakens from dormancy, the respiration is anaerobic or without oxygen. However, the sprout needs to quickly begin using oxygen in aerobic respiration to continue to survive and grow.
Cannabis Sprouts need access to both water and air
Seeds can be completely submerged in water during the first part of imbibition. However, if they are completely submerged after the radicle is exposed then the sprout will die from lack of oxygen. As soon as the seed cracks open and exposes the radicle it needs to have access to oxygen for aerobic respiration. This means that it needs some contact with air. However, it also needs continuous contact with water. To achieve the best results in the sprout and seedling stages it is best to use a grow media that will trap both air and water. As I explain below, paper towels work well for this during the early sprout stage and germination media like Jiffy Pellets or Rockwool cubes are perfect for young seedlings.
Germination Stage 3: Mobilization of Reserves and Early Growth
As metabolic activity resumes, the sprout will begin to grow. Cannabis seeds store most of their energy in their cotyledons in the form of starches and proteins. The plant uses energy from aerobic respiration to digest these starches and proteins into simple sugars and amino acids, which it mobilizes to grow the radicle (root tip) and hypocotyl (stem).
At this stage of germination, the plant must orient itself to grow properly. The radicle must push down into the soil or media and the hypocotyl must push the cotyledons (first leaves) up out of the soil or media. Both gravity and light help orient the plant to grow in the proper direction.
Apply Light but Keep the Radicle in the Dark
Cannabis seeds do not require darkness to germinate. However, the radicle is sensitive to light. Bright light will stunt the radicle and can lead to a failed germination. When seeds are germinated in paper towels it is best to keep the sprout in total darkness until the radicle is about half an inch long (about 1.25cm). However, as the cotyledons emerge from the seed casing, they will be looking for light to indicate the direction they need to grow. Therefore, when the radicle is longer than half an inch it should be placed in media which will protect it from light. Once the radicle is safely in the media, light should be applied to the top of the media to signal the direction of growth for the cotyledons.
Germination Stage 4: Photosynthesis
During the germination stage the plant relies exclusively on stored energy from the seed. This energy is limited, so the plant must quickly begin producing its own energy through photosynthesis. The young plant works to establish its radicle in the media and push the cotyledons up into the light to begin photosynthesis. Once the cotyledons open and receive light, the plant will begin photosynthesis. At this point, germination is complete, and the plant can start producing its own sugars, starches, proteins and fats.
Nutrients for Germinating Cannabis Seeds
The nutrients and supplements that we provide to our plants are not their food. Nutrients and supplements support photosynthesis. Therefore, they are not needed until the plant has begun photosynthesizing. Indeed, adding nutrients to the water used for imbibition can actually inhibit germination. It is best to use plain water at a neutral pH (7.0) to imbibe the seeds.
Once the cotyledons are open, the plant can use very small doses of nutrients. However, it is easy to overdo it and burn the plant. When and how to begin fertilization depends largely on the media that you are growing in. If you are growing in coco or other inert and unamended media, be sure to read “How to grow cannabis seedlings in coco coir”.
Cannabis Germination Strategies
There are many viable ways to germinate cannabis seeds. Different germination strategies may be more suitable for different growers. Therefore, before explaining my step-by-step guide to germinating cannabis seeds, I will review some of the more popular germination strategies.
Many growers begin germination by soaking seeds in water. This allows for faster imbibition of the seed because it is surrounded by water. It is a safe strategy to follow as long as you remove the seeds from the water before the seed actually cracks open. If you soak seeds, you should use plain (low EC) water with a neutral pH (7.0). Filtered or distilled water is best.
The Paper Towel Method
This seems like a make-shift hack, but wet paper towels provide an excellent air/water ratio for germinating seeds. They also allow you to precisely control the temperature of the seed/sprout during germination. As a result, using paper towels can speed the germination process considerably.
The paper towels should be fully saturated with water, but not dripping wet. I like to fold the paper towel so that there are two layers below and above the seed. You can then place the paper towels in an air-tight container to prevent them from drying out. I use pyrex containers. If you use a plastic bag, just make sure that you trap some air in the bag (don’t squeeze all the air out). The radicle does need some air, but there will be plenty, even in a sealed container. Place the sealed container someplace warm and cover it to protect the radicle from light.
The main drawback to the paper towel method is that it is possible to damage the young sprout when you transfer it to media. There are some easy practices to mitigate this risk. First, use cheap, single-ply paper towels. This prevents the radicle from growing between the plies. Second, place only one seed on each paper towel. This allows you to pick up the whole paper towel and avoid touching the sprout when you transplant to media. Finally, don’t keep the seeds in paper towels for too long. Once the root has grown to about 0.5in or 1.25cm, it is time to transplant it to media.
Seeds that are sprouted in paper towels should be planted into media root down. The seed head can be left very close to the surface with little or no media covering it. This will save the young seedling energy as it does not have to push the seed head and cotyledons up through the media. However, it can sometimes result in a “helmet head” where the seed casing does not come off the cotyledons. See my advice for dealing with helmet heads below.
Using Germination Media: Peat Pellets and Rockwool cubes
Germination media like Jiffy Pellets or Rockwool cubes provide an ideal air/water ratio for growing sprouts. In addition, they are well buffered and allow easy root growth. You can start seeds directly in germination media or transfer them to germination media after soaking seeds or the paper towel method.
I recommend Jiffy Pellets for plants that will be grown in soil or coco. Jiffy pellets come dehydrated and can be stored dry for decades. Once rehydrated, they provide an excellent media for germinating seeds. I prefer Jiffy Pellets over products like Rapid Rooters, which come hydrated and must be stored wet. Rapid rooters also have a premade hole that is considerably too large. Jiffy pellets are a looser material and you can create the hole that you need and then fill it in. To rehydrate Jiffy Pellets, simply soak them in low-EC pH-neutral water for 12-24 hours. A long soak is recommended to ensure thorough saturation of the Jiffy Pellet.
I recommend Rockwool Cubes for plants that will be grown in deep water culture or other hydroponic methods. Rockwool maintains its structural integrity better than peat plugs and it will not break apart and clog pumps in a DWC grow. Rockwool should also be rehydrated, but it is best to use water that has been pH adjusted to 5.5-5.8. This is because Rockwool often starts slightly alkaline. Using acidic water for rehydration helps to neutralize the pH.
Unsprouted seeds should be inserted pointy end down about 0.5in (1.25cm) deep. If the seeds are sprouted, you can bury the root and leave the seed head flush with the surface. Place the pellets or cubes in a humidity dome to preserve moisture and create high humidity. The Jiffy “Windowsill Greenhouse” is very inexpensive and it includes a small humidity dome which is perfect for this.
Planting Cannabis Seeds Directly in Soil
Growers who wish to avoid a complicated germination process may opt to start seeds directly in soil. This prevents transferring the sprout which makes it a simpler process to manage. However, there are drawbacks to planting seeds directly in soil.
When seeds are started directly in soil it becomes harder to balance the air to water ratio and control the temperature. In addition, the seed must orient itself within the media and push its cotyledons out of the soil, which requires additional energy. The combination of these factors adds time to the germination process and lowers the germination success rate.
Not all soils are appropriate for germination. Soils that are heavily amended can “burn” seedlings. Soils that have too much clay can suffocate them. If you want to germinate directly in soil, it is best to use soil that is designed for germination such as this Espoma Organic Seed Starter Soil.
Unsprouted cannabis seeds should be placed pointy end down about 0.5in (1.25cm) deep in the soil. The soil surrounding the seed should stay moist. It may take 5-10 days for the seedling to emerge from the soil. You should turn the lights on overhead by the third day and run them continuously until the seedling emerges.
Planting Cannabis Seeds Directly in Coco
Planting cannabis seeds directly in coco is challenging. I do not recommend it. Even well buffered coco requires a continuous supply of calcium and magnesium. It can be very difficult to satisfy both the needs of the coco and the needs of the young sprout. If you are growing in coco, I strongly encourage you to germinate seeds in germination media like Jiffy Pellets and then transfer the pellets to coco once the young seedling is established. Be sure to read “How to grow cannabis seedlings in coco coir”.
Cannabis Germination Tips and Tricks
Regardless of the germination strategy that you follow there are some tips and tricks that can help ensure a successful and rapid germination.
Scuffing Cannabis Seeds
Scuffing the seed coat prior to getting it wet will speed up the process of imbibition. The idea is to slightly roughen the outer layer of the testa (seed coat) to allow water to more easily penetrate the seed. If done properly, scuffing will increase the germination success rate as well as the speed. I gently scuff all cannabis seeds before germination.
To scuff seeds, it is best to use 240 or 320 grit sandpaper. Cut a square of about 3in per side and roll it around a pen with the grit on the inside. Use tape to secure the sandpaper tube and then slide the pen out. Place a single seed in the tube and cover the ends with your fingers. Give it 4-6 shakes, but that is it. If you scuff much more than 4-6 shakes or use coarser grit, then you could damage the seed.
Water for Germinating Seeds
In general, all the water used during germination should have a low EC (less than 300) or PPM (less than 150) and a neutral pH of about 7.0. This applies to the water for soaking seeds, wetting paper towels and rehydrating Jiffy Pellets. As mentioned above, if you are using rockwool for germination the water used for rehydration should be pH adjusted down to 5.5-5.8. Nutrients should not be added to the water until the cotyledons open, at which point the germination stage is complete.
Consistent Warm Temperature is Best for Germination
As I mentioned above, the ideal temperature for germinating cannabis seeds is 80-86 F (27-30 C). Seedling Heat Mats with a Controller allow you to create the ideal temperatures for germination. If you do not have a heat mat, then some growers will place their germinating seeds on top of an electronic device that runs warm such as a cable box.
To ensure the best germination, it is important to keep the temperature consistent. Sudden changes in temperature can shock the sprout and delay growth. The biggest risk of this occurs when you transfer a sprout from one media to another. To avoid this and ensure the best germination, the water, containers, and germination media should all be pre-warmed before introducing the seed or sprout.
Avoid Touching the Root
If you germinate in paper towels and then transfer the sprout to media, you should avoid touching the root. Using your fingers, tweezers or any other device may injure the delicate radicle. It is best to put each seed on its own paper towel so that you can pick up the whole paper towel to transfer the seed. You can use the paper towel to carefully set the seed in the new media which allows you to transfer without touching the seed with anything.
Carefully Remove Helmet Heads
During the germination process, the seed casing should come off the seed head, which allows the cotyledons to open. However, cannabis seeds will often emerge from the media with the seed casing still attached. This is a condition popularly referred to as “helmet head”. If helmet heads are not removed, the seedling may exhaust its supply of energy and die.
When you end up with a helmet head, it is best to moisten the seed casing and wait at least 24 hours for it to dislodge naturally. If it has not dislodged by the fifth day of germination, then you need to very carefully try to remove it manually. Be careful because if you pull too hard you can injure the seedling or even yank it completely out of the media. If the casing puts up any resistance, it is best to keep it moist for another 12-24 hours and try again.
Dr Coco’s Step-by-Step Guide to Germinating Cannabis Seeds
I use a germination strategy that is designed to maximize both speed and success. It relies on many of the principles and practices discussed above.
Step 1: Bring Seeds to room Temperature
I store my cannabis seeds in the refrigerator. The low temperatures put the seeds into a deep dormant state and ensure that they stay viable for a long period of time. Three days prior to germination I remove them from the refrigerator and allow them to warm up to room temperature.
Step 2: Gently Scuff the Seeds
Step 3: Soak the Seeds for Three Hours
After scuffing I put each seed into its own cup of pre-warmed water to soak. Using individual cups allows me to keep track of different seeds and makes the next transfer easier. I place the cups on my heat mat to keep the temperature warm. I set the temperature controller for 85F (30C).
Since they are scuffed, the seeds will imbibe water quickly. Usually seeds will float when first placed in water, but they will sink within the first two hours. If they have not sunk after two hours, I sometimes try to get them to sink. Whether they sink or not, I transfer them to paper towels after three hours. However, if you do not scuff seeds you could soak them for up to 12 hours.
Step 4: Transfer seeds to paper towels
I prepare the paper towels and pyrex containers in advance. I let the pyrex warm up on the heat mat as the seeds are soaking. I use half sheet paper towels and cut them in half again to create a little square. I then fold that over so there are two layers and pour the cup with water and seed into the pyrex with the paper towel. I make sure the seed is centered on one end of the paper towel and then fold the doubled paper towel over the top of the seed. With the seed secure in the paper towel, I drain off the excess water. The paper towels should be saturated, but not dripping wet. Finally, I seal the pyrex, place it back on the heat mat which is still at 85F (30C), and cover the pyrex with a towel to protect it from light.
After they go into paper towels, I wait 24 hours before checking on the seeds. Since they were scuffed, soaked and kept warm, most seeds will be open and the radicle will be emerging after 24 hours. I will check on them every 12 hours after that until the “tails” have grown about 0.5in (1.25cm). Most seeds are ready to transfer to germination media within 48 hours of getting wet.
Step 5: Transfer seeds to germination media
As the seeds are in paper towels, I rehydrate my Jiffy Pellets. I soak the jiffy in warm water and leave them soaking on the heating mat until needed. When the sprouts are ready, I remove the pellet from the warm water and place it in a tray. I break a tine off a plastic fork to use as a micro-trowel, which I use to open a hole for the root. I then pick up each paper towel and carefully manipulate it so that I can insert the root into the hole in the pellet without ever touching the sprout. I leave the seed head flush with the surface and close up the hole around the root. I place the pellets in a humidity dome to preserve the moisture and create high humidity and turn on the lights. Within a few hours the seed head will start to push above the surface. Within 2 days the cotyledons should open - and the sprout becomes a seedling.
The Next Steps
Once the cotyledons open your sprout has graduated from the germination stage and is officially a seedling! To help guide you on your cannabis growing adventure be sure to read the following articles and tutorials from our Table of Contents:
- How to Grow Cannabis Seedlings in Coco Coir
- Transplanting Cannabis Plants: Why, When & How
- Why You Should Train Cannabis Plants
- Growing Cannabis in Coco with High Frequency Fertigation
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