Compared to growing cannabis from clones, seeds offer a unique set of advantages and disadvantages.
As a grower, my goal is to always get ultimate high performance from my plants, from start to finish. I want them growing as fast as possible, ready for bloom phase as early as possible, with a survival rate of 100 percent.
When it comes to seeds, I’ve witnessed some mysteries worth taking the time to solve because they harmed my plants. Two of these conundrums involve how fast seeds germinate and how well they develop right after germination.
I breed my own seeds, but also purchase from reputable seed breeders. I noticed when I put 20 fresh seeds of the same age and same strain from the same breeder into rockwool cubes or other sterile media, some germinated faster, while some didn’t germinate at all.
In subsequent seasons, when I germinated cannabis seeds from that same strain using the same method — or several different strains at the same time — I noticed differences between the germination rate and rapidity inter-strain, as well as between different strains.
Some seeds would poke above the rockwool within one to two days, while some seeds in the exact same germination setting didn’t germinate for four to six days. Some took as long as 10 days. Worst of all, some didn’t germinate at all.
When you’ve paid $10 per seed, that result hurts your wallet, which is why I’ve undertaken the arduous task of paying close attention to seed germination and seedling care in every step of the process, painstakingly documenting my results along the way. And over several years of seed germination, I’ve experimented with crucial variables that had an impact on the success of my germination and seedling growth.
One of the most important variables to pay attention to is temperature. Recommendations for temperature of such media as rockwool cubes and root shooters range from 73–85° Fahrenheit. If you see that as a puzzlingly wide range of temperature variation, I have an explanation.
Every set of cannabis seeds has an ideal germination temperature, based on factors including strain genetics, the age of the seeds, the quality of the breeding, and the general conditions of the environment where the germinating seeds and their containers are placed.
Pure tropical sativa seeds germinate faster when the germination temperature is 77–84°F, but germinate one to four days slower, or not at all, when germination temperature was lower.
In contrast, Afghanica and Kush strains, which have genetics originating in the cold Hindu Kush mountain range, germinated best in the range of 73–75°F.
After analyzing several seasons’ worth of germination notes, I concluded that germination temps are best when they duplicate the likely conditions of the landrace genetics from whence they originated. This hypothesis further explains why tropical-origin cannabis seeds germinated best at warmer temperatures, but seeds whose genetics were sourced from mountainous regions and generally cold climates prefer cooler germination temperatures.
Also worth considering is that feminized seeds seem to be less viable than regular non-feminized seeds, while the older seeds are, the less viable they are as well. Find out more about germinating old seeds right here.
The Best Grow Lights For Cannabis Seed Germination And Seedlings
After my revelation about how mimicking the climate and soil conditions of the seeds’ genetic geographic location makes a difference in regard to germination, I expanded my analysis to include humidity, media moisture and lighting.
I found that if I germinated seed strains in, for instance, rockwool cubes in a dark place, it took them longer to germinate. It also caused the seedlings to stretch.
On several occasions, when I went to sleep at night, no seeds had germinated, but when I awoke the next morning, some had.
If they poked their heads above the media plane when it was dark, they tended to stretch and become gangly as they emerged with their primordial leaf set. Stretching isn’t good. If the young seedling develops too much stalk too fast, it becomes unstable and will keep falling over from the weight of developing leaf sets.
That’s why I now place a T5 fluorescent or LED grow light over my germination cubes from the time I begin germinating. A seed senses the presence of visible, ultraviolet or infrared radiation from above — the presence of a quality grow light over the germination area gave me better germination rates, faster germination, and seedlings with thicker, shorter, healthier stalks. I assume this is because in nature, infrared heat and radiation wavelengths are coming from the sun above, which seeds can sense.
Using a grow light to heat the seed germination zone, rather than using a seedling heat mat, produced a better germination rate and germination time for my grow. Again, this is likely because in nature, the heat and light are coming from above, while the root zone is cooler. With a heat mat, it’s the other way around — and totally unnatural.
Ideally, all growers should light their germination area 24 hours a day with a PowerVeg T5 fixture as soon as they place their seeds in the grow media. Just be sure to keep the light sufficiently above the germination plane so as not to overheat the media or burn the seedlings as they emerge from the medium. Using a high-output T5 grow light, I find that 10–12 inches from the germination plane is just about right.
I use the Lush Lighting Lumenator LED grow light for seedlings and clones, which I keep 17–22 inches away from the seedlings, lowering it as the seedlings establish roots and leaf sets, which is when they can handle more light intensity. For more information, check out this Lush Lighting technical data sheet.
Seeing as I’m based in the Northern Hemisphere, from mid-May through late August I give my seedlings a dose of direct sunshine from 9 a.m. to 4 p.m. every day that it’s not raining or cloudy. Using this method, I’ve seen noticeable improvement in seedling growth rate, stalk sturdiness, root mass and leaf development.
Of course, only do this if you’re sure the seedlings won’t be attacked outdoors by such pests as spider mites, aphids, thrips, caterpillars and mealybugs — and if you’re sure they won’t be spied by narks.
Plus, utilizing direct sunlight has another benefit for me: Seven hours of free sunlight means I don’t have to pay for electricity to keep my grow op powered.
Germination Zone pH And Seedling Fertilization
Now, let’s move on to the pH of the media zone. Most growers assume that the pH should be whatever is normal for the specific media being used. There’s an assumption that inert, sterile media such as rockwool and coco coir should be at 5.7 pH, while soil and soilless mix should be a little higher, say, 6.1–6.3 pH.
My experimenting suggests that similarly to how temperature affects different strains, some strains prefer a lower pH, while others crave a higher pH when it comes to germination rate, regardless of what root zone media they’re growing in.
Again, this may have something to do with the naturally occurring pH in the root zone of the seeds’ genetics. Consider testing seeds in a variety of pH conditions to see if they prefer a specific pH and have delayed germination in a different pH setting.
One of the trickiest parts of growing cannabis from seed is how to feed your seedlings. The seed itself has a tiny nutritional charge on board that fuels germination and the creation of primordial cotyledon leaves (i.e., the non-serrated first leaves seen on a germinated seedling).
If you’re germinating in sterile media such as rockwool cubes, you must feed the seedlings within four to five days after they germinate, but you have to be extremely careful not to overfeed them.
My feeding program during the first week post-germination consists of as much as half a milliliter per liter of reverse osmosis water of Sensi Grow pH Perfect base nutrients, along with half a milliliter per liter of B-52, and a quarter-strength dose of the root-boosting suite of products consisting of Voodoo Juice, Piranha, Tarantula and Microbial Munch. These supplements provide nutritional elements, vitamins, carbohydrates, and beneficial bacteria and fungi that create positive growth and spur root development.
I feed only once that first week, and have found that when I’m growing in inert media, if I don’t feed in the first week, the seedlings turn yellow, which is a sign of nitrogen deficiency. While I don’t want to overfeed, I want to ensure the babies have sufficient nutrition so they can form roots, a sturdy stalk, and at least one set of true (serrated) leaves.
In week two, I continue with this low-dose hydroponics nutrient recipe, as long as the seedlings’ stalks are tawny colored and leaves are green.
If the seedlings look particularly robust, I increase nutrient dosage a quarter to a half ml per liter at a time, until I’ve matched the manufacturer’s recommended dose for that particular age of plant, which is 1ml per liter. I’d rather underfertilize than overfertilize, which can result in burnt roots and may even kill the seedlings.
If I’m germinating in soil that has an in-built nutrients charge, I don’t use Sensi Grow for the first two weeks, but I do use the B-52, Voodoo, Tarantula, Piranha and Microbial Munch.
When week three arrives, I start using Sensi Grow at recommended dosage, along with the outlined recipe components. I also add Ancient Earth to the feed program at half strength, then increase it to full strength when seedlings have at least four leaf sets and look healthy.
I urge all cannabis cultivators to grow from seed at least one season per year, to try breeding seeds themselves, and to experiment with germination and seedling conditions and inputs as I’ve done. Doing this, you’ll soon discover the ideal sweet spot for the seeds you like to germinate, and your happy seedlings will reward you with faster growth, sturdier stalks, and eventually, fatter yields.