Before you begin...
Disclaimer: This information is only intended for government licensed medical marijuana growers and patients or for individuals who reside in areas of the world where the germination of cannabis seeds is legal.
The keys to seed germination are water and warmth; with a third important factor being cleanliness. It is absolutely crucial to keep all of your germinating tools sterile in order to prevent hostile fungal and bacterial infections from contaminating and killing your seeds before they have a chance to take root.
I do not recommend direct planting of cannabis seeds (germinating directly in the growing medium) as this often results in high failure rates. The seed is extremely vulnerable until it has produced a healthy tap root, and if you plant the seed directly in soil or other rooting medium it has a much greater chance of being attacked by pathogens before this can take place.
This is the method I personally use to get nearly 100% germination rates on all my seeds.
Step 1: Soak
Place seeds in a shot glass and soak in chlorinated tap water for 24-48 hours.
Do not use bottled or filtered water. Regular chlorinated tap water is preferred in this stage, as the chlorine helps to kill off pathogens and create a sterile environment for the seed to germinate.
The seeds will slowly absorb water through the shell over the course of the next two days, which triggers the seed into germination. Some seeds will begin germinating in as little as 12 hours after being in the water and you will see the shell begin to open and the tap root emerge. At this point the seed can be removed from the water and you can proceed directly to step 2. Others have a thicker shell that may take longer for the water to penetrate, so continue to wait the 48 hours or until the shell opens, whichever occurs first.
Step 2: Place Seeds in Damp Paper Towel
Drain the water from the shot glass over a bowl to ensure you don’t lose your seeds. Rinse the seeds gently with fresh tap water by refilling the shot glass, swishing the seeds around very lightly, and drain once more.
Fold a large sheet of paper towel into quarters and place on a small ceramic plate then dampen with fresh tap water.
Place the seeds in the middle fold of the paper towel and cover-over. The seeds should now be sandwiched between two layers on top and two layers on bottom of damp paper towel.
Step 3: Remove Standing Water
With the seeds now placed in the middle of the paper towel on the plate, drain off any excess water by tilting the plate and collecting in the shot glass. If any of the seeds happen to fall out, this way you will be able to catch them in the glass.
Step 4: Gently warm the seeds
Using a thermostatically controlled seedling heat mat, place the plate on top of the mat. Set the thermostat to 78 degree fahrenheit and insert the temperature probe between the paper towel next to the seeds. Once set, the display will show you the actual temperature of the probe and indicate if the heat mat is currently cycled on or off. Affix the suction cup to the plate to ensure it doesn’t slide out. Place a second ceramic plate on top. The ceramic plates act like a heat sink that will maintain a consistent temperature inside while allowing oxygen to enter through the small gaps. IMPORTANT: If the probe slides out of the plates into the cooler ambient air it will cause the heat mat to continue heating-up which could cook your delicate seeds. Make sure it is secure.
Note: I strongly recommend using a thermostatically controlled heat mat for this stage. Some choose to skip this step and simply put the plate of seeds somewhere warm like on top of a computer box. I discourage this. The temperature fluctuations can be significant in this type of environment and if the seeds get too warm or too cold it can seriously harm or kill them. A heat mat and thermostat will cost you around $50 and is excellent insurance. If you choose to skip this step, put the seeds somewhere warm, but not hot. 78 degrees is ideal.
Step 5: Monitor seeds until germination.
Keep checking on your seeds once a day to ensure the paper towel is still damp. If you live in a very dry environment, checking more often may be necessary to ensure the paper towel doesn’t try out. If it dries, they die! When inspecting your seeds be sure to check that the temperature probe remains secure.
Different strains germinate at different speeds, but you will often see the first tap roots emerging after 12-24 hours on the heat mat. Once the tap root has sprouted, you have successfully germinated the seed.
So what to do next?
Step 6: Plant
Once your seeds have sprouted a 1” or longer tap root, it’s time to place them in your medium of choice. I recommend using fresh, non-recycled medium with good drainage such as Promix HP, Sunshine Mix #4, or Coco Coir. It is important the medium you choose is fresh and hasn’t been recycled or amended with any nutrients. Fertilizer is a big no-no at this point. The sprout contains all the nutrients it needs to begin it’s life and adding any additional fertilizer at this stage will only harm it.
To plant; simply fill a small seedling cup with your medium, and poke a hole with your finger that is as deep as the seed’s tap root. With extreme care, grab the spout by the seed-head and place into the hole such that the seed head is just under the surface of the medium with the tap root extending down into the hole. DO NOT PLANT TOO DEEP.
Carefully fill in the medium around the sprout and then dampen (NOT SOAK) with chlorinated tap water. I find using a spray bottle filled with tap water works wonders for this stage. It allows you to mist the medium until it is evenly damp but not soaking wet.
At this point you can then move your seedling cups to a warm location with indirect light. Keep the soil moist by gently misting it daily, and within a week or so your seedlings will emerge.
Congratulations, you’ve now grown a healthy cannabis seedling.
Professor Sprout