The seedling stage of cannabis plants follows on from germination. Read more about the nutrition they need and the kind of light they prefer. If you want to learn about the different elements that can affect your cannabis seedlings, how to identify the problems and fix them, make sure to read along! Seeding Cannabis National Weed and Seed Program — U.S. Department of Justice, Executive Office for Weed and Seed The U.S. Department of Justice’s Weed and Seed program was developed to
The seedling stage of cannabis follows on from germination. You will be able to tell when it has begun when your shoots start to develop a second set of leaves. These will look different to the embryonic cotyledons. They will be bigger, with a long serrated edge – a look that is much more associated with cannabis plants. However, these new leaves will only have one “finger”, instead of the 5 or 7 normally seen in adult leaves.
After this your cannabis plants will start to grow a third set of leaves, these will tend to have three fingers. This will be followed by more and more leaves, with each one beginning to resemble the expected cannabis leaf shape more and more. As mentioned, the most common and expected is a 5 or 7 finger leaf, but do not be surprised if you end up with 9 or even 11 fingers!
The seedling stage is usually over when you start getting leaves with their maximum amount of fingers. Other indications will include a stem with a thickness of around 4-6mm and a height of around 3-4 nodes. During this stage the seedling will also try and develop a strong root base, this will allow for strong future development and nutrient intake. Depending on where you grow, the seedling stage can take roughly 2-3 weeks indoors and 4-6 weeks outdoors.
As an extra tip, it is usually advisable to set up a small, weak fan to blow on at your seedlings. This will help them gain fresh air and encourages strong growth. It does this by giving the plant something to resist. As the fan blows at your cannabis plants, your seedlings will recognize that they need to put extra effort into growing and developing their structural integrity to withstand possible future sources of resistance.
You will know the time to transplant your seedling to a larger grow medium when you start seeing signs of its developing root base. Chances are your seedlings will be growing in individual, small pots. As their roots grow they will start to exit out the holes in the bottom of these pots. This shows that they need more room and are ready to be moved. Be very careful transplanting them though, roots are very fragile and any damage can have very serious implications into your cannabis plants’ ongoing health.
Light during the seedling stage
There are a lot of cultivators out there who put their seedlings under fluorescent tube lighting. Due to the weakness of florescent lighting they need to be placed quite close to your seedlings – about 5 cm above them, (don’t worry, they do not produce much heat, so this is fine). This causes your cannabis seedlings to grow broad – otherwise the plants need to “search” for light and you end up with long plants with thin, weak stems that will easily fall over. This is fine if you are willing to offer your plants support, but it is not a good foundation to lay if you want healthy, vibrant plants in the long run.
Some cannabis growers use HID lighting for their seedlings. HID lights produce a much better quality of light for growing cannabis, leading to stronger, healthier plants. The offset is that they produce a lot more heat – something your marijuana seedlings are very vulnerable too. For this reason it is important to make sure your lights are at the correct height above your plants. Start by having your HID lights 80cm above your plants, lowering them by 5cm each day until you are in the region of 40-60cm (depending on the wattage of your bulbs). Also, always perform the ‘hand test’ to see if things are getting a bit to hot.
In terms of color-band, it is best to go for a bulb within the blue spectrum. This will encourage strong and healthy stem and leaf growth.
During the seedling stage, most cultivators will use an 18/6 photoperiod. It is also possible to do a 20/4 period, with some cultivators going as far as using a 24/0 period to really boost growth.
Nutrition during the seedling stage
Generally speaking, seedlings are pretty self sufficient. However, as stated in our germination article, using a seedling/germination soil is recommended. This will have the finer, small amounts your cannabis seedlings can use. You should note, cannabis seedlings are extremely vulnerable to overfeeding, any excess will cause root burn, killing off your plants.
As a result, novice cultivators are strongly advised from adding anything to your soil other than clean, distilled water (pH of 6.5-7). Your seeds should have everything they need and will need minimal extra input from you. Just make sure they have the water and light they need and they will do fine. Once your seedlings have grown, they will enter the vegetative stage of their life cycle.
Common Cannabis Seedling Problems and How To Fix Them
Problems with seedlings are common and can end up affecting them further into their life cycle so it’s vital you detect and fix them as soon as you can. Yellowing or deformed leaves, burnt tips, or even slow growth are signs of cannabis seedling problems, even though your seedling may be able to recover, it may have a toll on the final size and yields of your cannabis plants. It’s definitely not hard to detect when something’s wrong, but if you’re a new grower, first you should know what a healthy seedling looks like.
1. Healthy Cannabis Seedlings
Cannabis seedlings start with two tiny round leaves called “cotyledons”, these leaves are already formed inside the seed and open up once the seed has been successfully germinated, after a couple of days, the first serrated leaves will appear, which indicates that your weed seedling is starting to grow.
As your seedling start developing, the first pair of true leaves will appear, the true leaves are the typical fingered leaves everybody knows, all of the leaves up to this point should be bright green, if not, it’s a sign that something is wrong, to help you diagnose what you may have, here are the most common cannabis problems.
Overwatering is one of the most common cannabis seedling problem amongst growers, even though weed plants need water to grow, they also need oxygen to properly develop, and when overwatering, you may end up drowning your plants because of the lack of oxygen. What about plants grown in hydroponics? Well, in hydroponic setups, about ⅓ of the roots are kept out of the water, this way they can breathe at the same time that they absorb water so even though the roots are in the water, they still get the oxygen they need.
When your plants don’t get the amount of oxygen they need, the leaves will start getting droopy and if you don’t treat it for long, the leaves will start to get yellow. If you are seeing any of these symptoms, it’s most likely the problem is being caused by any poor drainage or watering too often.
How to fix it
- Don’t leave plants sitting in runoff water.
- Get better containers such as Smart pots or Air pots.
- Mix perlite into the soil to increase drainage and oxygenation.
- Make drainage holes on the bottom of the container to allow water to drain.
Just like overwatering, underwatering is very common, especially among new growers who want to prevent overwatering and it can be quite confusing because the symptoms are basically the same as when overwatering.
It’s essential you ensure your plants have access to water at all times, the roots should be kept moist always because plants are constantly losing water through the process of transpiration and they need to be able to replenish the water in the leaves. When there’s not enough water, cannabis plants stop performing their basic processes and dry out, eventually killing them so even though you should be careful when watering, you should definitely keep your plants watered to avoid seedling problems.
How to fix it
- Ensure the top part of the soil is always moist.
- Mix soil with coco fiber or vermiculite to improve water retention.
4. Nutrient Problems
Just like the symptoms of overwatering or underwatering, plants that suffer from a nutrient excess (overfeeding) will start to get yellow leaves or yellow spots, burnt tips, or show slower growth. Seedling problems related to nutrients are usually caused by giving nutrients too soon, giving too many nutrients at once, or “hot” super soil or pre-amended soils. Giving too many nutrients at a time can cause problems overnight, so we recommend watering your seedling with plain water and taking a look at the following table so you prevent any seedling problems related to nutrients.
|The ideal water for seedlings|
|Coco, clay pellets, and hydro||5.5-6.2||300-400|
Have in mind that these are estimates and you should check every day for problems and lower or increase these numbers if you see signs of deficiencies. Giving nutrients too soon will overload the soil, and consequently, your seedling so remember that you shouldn’t feed for the first couple of weeks or at least give a low nutrient dose.
This can also happen with organic super soil, even though it’s organic, you need to wait until your super soil isn’t “hot” anymore, “hot” soil means that the mix is still undergoing biological activities so you will have to wait around 30-45 days before you can use it, although this is not the case with all super soils so make sure you get more information on the product you’re using to avoid seedling problems.
How to fix it
- Ensure you adjust the nutrient dose according to the medium you’re growing in.
- Wait at least 10 days before you start feeding your plants.
- Read the instructions on the products you’re using.
5. Excessive Heat
Excessive heat can also affect your plants, which will end up showing signs of heat stress, you will see the edges of the leaves turning up like tacos and they will start to get dry and crispy, and in more extreme cases, the leaves will start showing a yellowish-green color.
This can be caused by elevated temperatures, low humidity, or even the fans being too strong, but luckily, this can be easily spotted before your plants start showing the symptoms because you will see the soil is dry and sometimes it will start to crack.
How to fix it
- Make sure the temperature and humidity are at the right levels.
- Place your hand under the light fixture, if it’s too hot for you, it definitely is for your plants.
- Ensure your fans are not too strong for the stage your plants are in.
6. Too Much (or Too Little) Light
Another common problem among new growers is not providing enough or providing too much light in the seedling stage, if your seedlings are not getting enough light, they will start stretching and the stem will get super long, which is a bad thing because they can easily snap and there’s no way to fix it.
Now, when your seedlings are getting too much light, or the lights are too close to them, the seedling will get dehydrated and the leaves will get burnt, showing symptoms like burned and wrinkled leaves.
How to fix it
- Adjust the light fixture’s distance from the seedling every day, try to find the sweet spot.
- Use CFLs instead of potent LEDs or HPS to avoid this kind of problem.
7. Seed Shell Stuck on Seedling
Sometimes, when a seedling comes out of the substrate you’ll see how the seed shell is stuck on the seedling and won’t come off naturally. When this happens, your seedling won’t be able to develop properly and you’ll probably see a lot of stretching, and if left for too long, the seedling can end up dying. This happens because of the humidity levels, so in order to minimize the damage, there are a couple of things you can do.
How to Fix It
As mentioned, this happens because of humidity levels, low humidity levels to be precise, so what you need to do is hydrate the seed shell. So go ahead and spray the seedling with plain water or just drop one or two droplets of water on the seed shell, this will hydrate it enough for the seed shell to fall off. Keep in mind that sometimes the seed shell falls off but a membrane covering the cotyledons can remain stuck and your seedling will not be able to open so make sure to grab some tweezers or remove the membrane with your fingers but do it very, very carefully.
If you need to do it asap and don’t want to wait for the seed shell to fall, you can remove it by hand without spraying it but keep in mind that if the seedling’s roots have not grown enough, you can end up removing the seedling from the soil so do not use excessive force. It’s highly recommended to hydrate the seed before just to avoid shock or stress, especially to avoid removing the seedling from the substrate completely.
- Make sure to keep the humidity levels in range with the help of a humidifier.
- Place a plastic dome (like a cut-out plastic bottle or plastic cup) on top of the seedling to help keep higher humidity levels.
8. What To Have in Mind During The Cannabis Seedling Stage
In order to avoid all the cannabis problems mentioned throughout the article, here are the main tips that will help you avoid them and keep your cannabis seedlings healthy and happy.
The Perfect Environment
The relative humidity and temperature will directly affect how your seedling grows so make sure the light is not too strong but your cannabis is still getting enough light and the temperature is around 21-23 ºC and the relative humidity ranges from 70-80%. Failing to provide good conditions can affect plant growth and can ultimately kill your plants if left untreated for too long, so here’s what to expect in the different conditions:
Substrate is too wet
If the substrate is too wet, the seeds can drown. Despite seeds being germinated in water, it’s not okay for the substrate to be extremely wet so always make sure the substrate is moist but not soaking.
Substrate is too dry
Cannabis seeds need moisture to germinate so make sure the substrate is moist but not excessively wet as excessive dryness can make your seeds not germinate and die.
Watering cannabis seedlings properly is the hardest part for beginner growers, watering too much can result in an overwatered cannabis plant, and watering too little can result in an underwatered weed plant so make sure you start watering with around 100 ml and increase the amount according to how your plants grow.
Seeds were planted too deep
1 – 3 cm is the deepest you should go in order to provide support to the roots and cover the seeds with the substrate. If you plant the seeds too deep the seedling could have a hard time sprouting out of the substrate so do not plant it too deeply.
Environment is not warm enough
Seedlings prefer warmer temperatures ranging from 22 -26 celsius and will grow at a slower rate in colder temperatures.
Environment is too humid
It’s recommended to use a plastic dome for newly born seedlings but remember to remove them as soon as the seedling starts developing the first pair of one-fingered leaves after the cotyledons as a high humidity can cause damping off, which results in seedlings folding over and dying.
Marijuana light burn can indeed hurt your plants if the light is too strong. Seedlings are more fragile than adult weed plants so make sure you dim down the light or adjust the fixture’s light to avoid stressing them. Also, if your seedlings are stretching a lot it means they need more light so, if this happens, increase light intensity or place the light fixture closer.
9. FAQs About Cannabis Seedling problems
Here are the most frequently asked questions about cannabis seedling problems to help you understand a bit more and help you deal with them. Just remember that different problems may have similar symptoms so make sure you are 100% sure about what the problem is before taking drastic measures.
“Why are my seedling’s leaves turning yellow? Could it be a cannabis nutrient deficiency?”
When the leaves start yellowing it’s probably a sign of nutrient problems, this means they’re either lacking nutrients, are getting too many nutrients or getting the wrong type of nutrients.
“When should I remove the plastic dome of the seedlings?”
The plastic dome helps raise humidity for faster germination so you can remove it as soon as your plant has completely developed a pair of leaves (after the cotyledons).
Remove the plastic dome once the seedling has developed the first pair of leaves after the cotyledons.
“Why are my cannabis seedling’s leaves curling down?”
This usually happens when you overwater your seedlings or when they’re exposed to higher temperatures so make sure the temperature ranges from 20 – 25 ºC and pay attention to how much water you’re watering with.
“When is it safe to put my cannabis seedlings under the light?”
Well, your seedling needs to be under light since germination but you can use a 15-20 W fluorescent light during the first 1-2 weeks and once the first pair of true leaves have completely developed, you can go ahead and place it under the LED or MH bulb.
“Is there a better light schedule for marijuana seedlings?”
The best light cycle for both autoflowering and photoperiod cannabis seedlings would be 18/6 from seed.
“Is the substrate super important for seedlings?”
Of course, the substrate mix is super important for a healthy start. Some growers prefer a “light mix” which can provide nutrients for the initial weeks and others make their own blends with perlite and coco fiber. There’s no best substrate but a substrate mix that allows for good oxygenation and water retention is ideal.
“Why are my marijuana seedlings growing so slow?”
This is the hardest question because it can be caused by several things. Your cannabis seedlings may be lacking nutrients or it could be caused by lack of proper lighting and extreme temperatures or humidity.”
“How far should the grow light be from the cannabis seedling?”
If you’re using a CFL light, the lights should be 5 – 10 cm from the seedlings. If you’re using HPS or MH, the light should be around 25 – 40 cm from the seedlings and if you’re using LEDs, the fixture should be at around 75 cm from the seedling with 40% light intensity if possible.
“How long does it take for the seeds to germinate and the seedling to come out of the soil?”
The germination process is usually quite fast but depending on the quality of the seeds, it may take up to 5 days or even more. Once the seeds have germinated and been planted in the pot, the seedling should take around 3 days to come out of the soil if the growing conditions are proper.
“Is it possible to know my plant’s sex during the seedling stage?”
No, you’ll only be able to tell whether your marijuana plant is a male or female during the pre-flowering stage. This happens because cannabis plants need to sexually mature in order to show either male pollen sacs or female stigmas.
10. In conclusion
Marijuana seedlings are super fragile and sensitive so you should take good care of them, avoiding cannabis growing problems at this stage is vital because even though your baby plants may recover, the size and structure may be affected, which will end up affecting your harvest.
If you have tips you can share with fellow growers to help them take care of their baby plants, feel free to leave a comment in the comment section below!
National Weed and Seed Program — U.S. Department of Justice, Executive Office for Weed and Seed
The U.S. Department of Justice’s Weed and Seed program was developed to demonstrate an innovative and comprehensive approach to law enforcement and community revitalization, and to prevent and control violent crime, drug abuse, and gang activity in target areas. The program, initiated in 1991, attempts to weed out violent crime, gang activity, and drug use and trafficking in target areas, and then seed the target area by restoring the neighborhood through social and economic revitalization. Weed and Seed has three objectives: (1) develop a comprehensive, multiagency strategy to control and prevent violent crime, drug trafficking, and drug-related crime in target neighborhoods; (2) coordinate and integrate existing and new initiatives to concentrate resources and maximize their impact on reducing and preventing violent crime, drug trafficking, and gang activity; and (3) mobilize community residents in the target areas to assist law enforcement in identifying and removing violent offenders and drug traffickers from the community and to assist other human service agencies in identifying and responding to service needs of the target area. To achieve these goals, Weed and Seed integrates law enforcement, community policing, prevention, intervention, treatment, and neighborhood restoration efforts. The Weed and Seed program is being implemented in more than 150 communities across the country.
The Executive Office for Weed and Seed (EOWS) within the Office of Justice Programs is responsible for overall program policy, coordination, and development. EOWS also serves to enhance the law enforcement and prosecution coordination among Federal, State, and local agencies, and coordinates with other cooperating programs and agencies such as Ameri-Corps, Empowerment Zones/Enterprise Communities, and the Comprehensive Communities Program.
Paul Casagrande, Program Manager
Executive Office for Weed and Seed
U.S. Department of Justice
810 Seventh Street NW., Sixth Floor
Washington, DC 20531