A good start is always the key to a good finish, so a solid understanding of the ins and outs of marijuana seedlings can make the difference between success and frustration. Cannabis seedlings are extremely fragile. Armed with nothing but tender roots and a small set of cotyledons, your seedlings can be brought down by minor stressors in just a few hours.
Let’s dive deep into caring for your baby marijuana plant, so you know exactly how to look after your growing seedling and ensure it grows into a healthy, mature cannabis plant.
Germinate your seed properly
The first step of the growing journey is seed germination. The germination of a cannabis seed can take anywhere from 12 to 72 hours (in optimal conditions) to a few days and even longer. This can have many causes, from the age of the seed (old seeds have poorer germination rates and take longer) to chance.
If you store your cannabis seeds properly and give them the best environmental conditions to germinate, the chances of success increase. Note that the length of germination time doesn’t necessarily have anything to do with how healthy your plant will be in the long run.
How to germinate marijuana seeds
The simplest germination method is to place your seeds in a glass of water and leave them in a cupboard at 68–77 °F (20–25 °C) for 24–48 hours. Most viable seeds float at first and sink to the bottom of the jar after a few hours of soaking. Do not keep the seeds underwater for more than 48 hours, or they will rot.
If your seeds do not germinate after 48 hours in water, switch to the paper towel method. Place the marijuana seeds on a paper towel at least ½ inch (1 cm) apart and cover them with two other water-soaked paper towels.
There is a possibility that the towels will dry out, killing the new seeds. Therefore, we recommend placing the paper towels under an upturned bowl or between two paper plates (or normal plates). You can also build a germination station at home by placing a plastic dome over a plate on a heating pad.
Alternatively, we strongly recommend using Rapid Rooters for your hydroponic application (or any other grow setup) as they are much more user-friendly and usually achieve much better germination rates. The texture of Rapid Rooters ensures that the seeds stay put and don’t fall further into the hole once you’ve closed it.
Rapid Rooters are easy to use – you simply place your cannabis seed in the Rapid Rooter (point down), keep your seed warm and slightly moist in a tray with some water, and let the Rapid Rooter do its work. The resting place for each Rapid Rooter has a hole at the bottom so that the water in the tray is sucked upwards.
It is important to ensure that the seeds have access to water throughout germination, regardless of which cannabis germination method you end up using. If the seed’s root breaks through the shell and the water around it has dried out, the seedling will die.
Plant your marijuana seedling
Don’t worry, you can’t mess this part up. As long as the seed makes it into the container, everything should be fine.
Within the first week of the seeds germinating, you will notice that some seeds germinate immediately and others take a little longer. The small white tendril that emerges from a cannabis seed during germination is the plant’s first root, known as the “tap root”.
As soon as you see the first signs of tap roots sprouting from your seeds, they are ready for planting. You can plant any seeds that have germinated straight away, or leave them for another day or two so the others can catch up.
If you germinate your seeds in a paper towel, there is a risk that you will injure the taproot (the small white root that grows out of the seeds) if you move the germinated seeds, so be careful when checking to see if the seeds have germinated. You don’t want to touch the little white taproots with your fingers, so either move the seeds carefully or use tweezers.
Where to plant your seedling
For rapid growth, it is better to plant young seedlings or clones in a very small container, such as a disposable plastic cup. In addition, even outdoor gardeners grow their seedlings in a controlled environment indoors because they are very delicate, and then plant them in the ground when they are a little bigger. It is best to start indoors and bring the marijuana seedlings outside when they are healthy, robust, fast-growing, and no younger than two weeks after germination.
Avoid leaving the seedlings in the dark for 24 hours after germination (a common piece of advice in growing forums), as the lack of light will force the seedlings to stretch abnormally. Also, you should ensure that the seeds or seedlings are always kept warm and moist, that their roots are not exposed to light and that they are planted immediately.
Leave your young plants in a tray with water until their roots are well developed and ready to be transplanted to their final destination. While you wait for the container to dry out, your cannabis roots will be in a humid environment.
Transplant your seedling into a new pot
After planting your germinated seed in your chosen growing medium, the tap root – and perhaps a few tiny early offshoots of the taproot – will grow longer and longer, pushing the seed upwards. And after the husk has broken through the surface of your growing medium, the first leaves (these first round leaves are called “cotyledons”) will emerge from inside the cannabis seed.
The stem pushes the leaves upwards while the main tap root digs straight down to support the seedling. The next leaves after the cotyledons are the first “real leaves” of the plant and have serrated edges (serrations). These are the first leaves that your seedling will grow all by itself, unlike the cotyledons that were already formed in the seed.
If you look closely, you can see that some of the newer leaves on your plant actually have 9 fingers. It is normal for there to be some variation between the leaves – some plants have leaves with 11 or even 13 fingers. The plant is now ready to focus its energy on vegetative growth, so it needs to be moved to a larger container.
Once the seedlings have outgrown a small container, you can transplant them into a larger container, and the seedlings will be much more robust. Seedlings can grow quickly, and many gardeners have been surprised to find that plants have actually grown into the light overnight.
Try checking the roots of your seedlings after about a week. However, we recommend not to go by time, but to transplant the seedlings as soon as they have developed at least 3 nodes and 4–5 sets of true leaves.
Moreover, the right time to transplant your cannabis plants is when they have an established, stable root system. Unfortunately, transplanting seedlings is anything but an exact science; instead of following a strict calendar or schedule, it’s all about paying attention to the plant and knowing what signals to watch for. In general, when you can completely remove a seedling along with its soil, it is ready for transplanting.
How to choose a pot
Some gardeners grow their seedlings in a solo pot or a peat pot so that they can simply cut off the pot for easy transplanting again. And according to experts, marijuana plants are protected from rooting if they are grown in air pots or smart pots (fabric pots) because they let air in from the sides.
But what pot size should you use for your seedlings? The exact pot size will depend on the strain you are growing and the size of your growing space, but most home growers use pots with a capacity of 1.5–4 gallons (5–15 liters). Some indoor growers choose to transplant their plants directly into 3-gallon (12 liters) pots, but you can go above or below this, depending on the variety and grow setup.
Just remember that if a plant is put in a pot that is too big, the roots will not be able to expand as far and soak up as much water.
How to minimize transplant shock
When transplanting marijuana seedlings from a container, carefully turn the pot upside down and squeeze the edge of the container. Be sure to place your free hand against the soil line to prevent the seedling from falling to the ground.
Once you have transplanted your seedlings into their new pots, give them 3–7 days to adjust. Every time you transplant a germinated seed, it can cause stress as the young plant has to get used to its new environment. Remember to treat your seedlings very gently when you replant them. If you want to transplant your seedlings again, you should only do this when they are well grown and have some more leaves (nodes).
Any tiny damage to their roots can cause a lot of stress from which young and fragile plants can be slow to recover. If you touch or break the root, the seedling may still survive, but any damage to the root will definitely stunt and slow down growth right at the start.
If you are growing feminized seeds, transplanting is not a big problem, as these plants have time to recover from the stress. Remember that you can (and should) repot feminized photoperiod plants a few times to maximize development, i.e., you don’t need to transplant your seedlings into a large pot straight away.
However, it is best not to subject autoflowering varieties to unnecessary stress because of their short life cycle. Autoflowers do not like to be transplanted, and it is best to grow autoflower in the same container from seed to harvest. One of the best methods for germinating autoflowering cannabis seeds is to use specially made starter cubes and seedling plugs.
Some growers look down on them, but they are definitely handy if you need to transplant without stress. By using a seedling plug or cube, you can just wait until you see roots coming out. Just place the seeds in the cube or plug, add water as directed, and they will automatically get the perfect conditions for germination.
Afterward, the germinated seed can easily be transferred directly to the next growing medium or container. As your seed is already in its final place, your new seedling will immediately adapt to the environment.
Water your seedling properly
You should transplant your seedlings just before they grow out of their pots. One of the advantages of starting young plants in a large container is that you won’t have to transplant them into larger containers when they get older.
But if you have planted your seedlings in a large container, make sure that the young seedlings do not get too much water. With a larger container, you will have to wait longer between watering, and during this time your plant roots will receive less oxygen.
A large plant will soak up all the water quickly, but with seedlings, you are basically waiting for the growing medium to dry out on its own. If you water seedlings or clones in a very large container, they will quickly use up all the oxygen, and the size of the container will prevent the growing medium from drying out. Your cannabis seedlings and clones will definitely survive, but they just won’t grow as fast in the first few days or weeks because they won’t get as much oxygen.
If you plant young seeds in a small container with holes in the bottom, the growing medium dries out much faster, so you can water more often.
Nevertheless, if you decide to put your seedling in a large pot, you will probably need to water the whole container lightly once and then water very small amounts and only near the seedling, gradually expanding this area and increasing the amount of water.
When to water your seedling
Watering cannabis seedlings properly is the hardest part for beginners. Too much water can lead to an overwatered cannabis plant, and too little water can lead to an underwatered weed plant.
Once the plant has formed a few leaves, you should start watering your cannabis normally so that the water runs off the bottom. Be careful not to overwater the plant at the seedling stage, though – its roots are so small that it does not need much water to thrive. Be mindful that too much water at this stage can drown the delicate marijuana seedlings.
Overwatering is one of the most common cannabis seedling problems among growers because although weed plants need water to grow, they also need oxygen to develop properly. If you overwater, the plants may die due to a lack of oxygen. Furthermore, water standing in the pot for a long time and can lead to root rot.
If you have planted your young plant in a large container, try to give just a little water at a time (enough to wet the area around the seedling’s roots) until the plant is growing vigorously. You will probably only need to water them every 4–7 days, but this will depend on your climate and setup.
Just like overwatering, underwatering is also very common, especially among beginners who want to avoid overwatering, and it can be quite confusing because the symptoms are basically the same as with overwatering.
An important note: Some growers get lucky and happen to have water with the right pH, but if you notice deficiencies and problems with your seedlings, be sure to take the time to learn about the pH of marijuana roots and how it affects the overall health of the plant.
Give your seedling enough light and warmth
The heat from a grow lamp improves the germination rate, and the light can help your new cannabis seedlings open their first leaves. As soon as the seedlings have developed their first two leaves, you can remove the lamps to a distance of 4 inches (10 cm), as long as the lamps are not too hot. Nonetheless, keep a close eye on your seedlings so they don’t grow too close to the grow lights and get burned. This is shown by the leaf tips erecting and curling.
Since your seedling needs to be under light starting from germination, you can use a 15–20W fluorescent lamp for the first 1–2 weeks. Once the first pair of true leaves has fully developed, you can put it under an LED or MH lamp. Temperatures should remain warm, and the bulbs should be placed close to the plants and moved up as the plants grow.
The rule of thumb is: If you are using HPS or MH, the light should be about 10–16 inches (25–40 cm) away from the seedlings, and if you are using LEDs, the light should be about 30 inches (75 cm) away from the seedlings, preferably with a light intensity of 40%.
But if you plan to grow your marijuana seedlings under high-intensity grow lights (such as HPS or MH grow lights) later, you should grow them with lower-intensity fluorescent lights or compact fluorescent lights (CFLs) first. Otherwise, keep your high-intensity grow lights a few meters away at first and slowly move the lights closer as your seedlings get older.
If you see your seedling staying short and its leaves not growing, or worse, turning yellow and dry, the light is too scarce.
How to determine the correct temperature and humidity
Environmental conditions are crucial for growing healthy cannabis seedlings, and the most important conditions to control include temperature and relative humidity. They directly affect the growth of your seedling. So make sure the light is not too strong, but your cannabis still gets enough light, and the temperature is between 70–73 ºF (21–23 ºC). Meanwhile, the relative humidity should be between 70–80%.
If temperatures are too high or too low, the seedlings will inevitably show stunted growth. If this is the case, adjust the ambient temperature and observe the changes.
Why the dark cycle is important
Once germinated, baby plants need a lot of light, 18 hours per day to be exact (although you can give them 24 hours of light per day). During the vegetative stage, 16 hours per day is ideal. Indoor growers can trigger the flowering cycle by reducing the amount of light marijuana plants receive from 16 to 12 hours per day. Outdoors, flowering occurs naturally when the plant receives less light per day as summer turns to autumn.
Many experienced gardeners believe that nighttime is important for plants because it gives them a chance to rest, which protects them from overwork. There is also a theory that the root system grows more actively during the dark and cool hours. So keep this in mind if you decide not to turn off the lights in the evening or water your plants before turning off the lights.
Feed your seedling properly
Just like the symptoms of overwatering or underwatering, plants suffering from nutrient problems will show yellow leaves or yellow spots, burnt tips, or slower growth. This means that they are either getting too few nutrients, too many nutrients, or the wrong kind of nutrients.
Usually, nutrient burn (overfertilization) occurs when seedlings are fed too early or too heavily. This can also happen with organic super soil, even if it is organic. If you have made your own super soil, you will need to wait until it is no longer “hot”.
“Hot soil” means the mix is still going through biological activities, so you cannot use it for 30–45 days. This may not be the case with all super soil, however, so make sure you get more information about the product you are using to avoid problems with the seedlings.
The first signs of nutrient burn are dark green leaves with burnt tips. If left untreated, nutrient burn will also cause the leaves to bend upwards. The best way to avoid it if you are growing in soil is to choose light mixes and avoid extra fertilizer for the first week or two.
Grow your weed seedlings in soil, and you will probably never need to feed them until they enter the vegetative phase sometime after two weeks. After all, a cannabis seedling only needs small amounts of nutrients, and its needs will increase as the plant gets bigger and stronger.
Another thing to note is that if you feed your plants too soon after transplanting, they are unlikely to absorb all the nutrients from the growing medium, leading to problems further down the line, e.g., nutrient deficiency. You should do the first feeding when the plant is at least 2 weeks old (1 week for risk-takers and rule-breakers). The presence of harmful organisms can also prevent nutrients from moving around and the roots from absorbing them.
Here are the most frequently asked questions about cannabis seedlings to help you better understand and deal with them.
Can you grow seedlings outdoors?
Believe it or not, cannabis grows in the wild, but you probably paid a pretty penny for seeds and don’t want to expose your precious seedlings to the elements too soon. That said, one of the biggest advantages of planting the seeds directly into the growing medium is that you don’t have to worry about your young seedling suffering shock when transplanting.
So when is it more or less safe to start growing outdoors? Look at the weather forecast and choose a period when there can be no more early morning frost and the outdoor temperature is at least 59 °F (15 °C) in the morning.
Is sunlight good for the seedling?
We used to think that marijuana seedlings should not be in direct sun all day, but some experiments have shown that this rule can be ignored in the spring. Too much sunlight can be deadly for very young plants, though, so you should shade them to protect them from the full sun. In the summer, it is best to expose your seedlings to direct sunlight for a few hours only in the morning and evening when the air is cool, but never around midday.
Should cannabis seedlings be flushed?
Cannabis seedlings and flushing are two things that don’t go well together.
Is it advisable to use Rockwool to grow seedlings?
Rockwool is dusty and must be thoroughly rinsed before use. To put it simply, the dust can be harmful to your health. If you inhale Rockwool dust, small strands or fibers can enter your lungs, and it is not known if these fibers can ever leave.
If you choose to use Rockwool, germinate your seeds using another method, such as the paper towel method, and then transplant them into the Rockwool cubes after roots have already formed.
Get a handle on your marijuana seedling problems
Generally, it takes between 10 and 32 weeks, or about 3 to 8 months, to grow a marijuana plant from seed. If you want great results at harvest time, start building your success early with proper cannabis seedling care. This will save you time and ensure that your babies move on to the next phase (the vegetative phase) full of vigor and in the best possible shape.
With a solid understanding of seedlings and their needs, the important seedling stage can be much less daunting. Start by germinating your cannabis seeds using one of the recommended options to ensure a germination rate as close to 100% as possible. Never forget that repotting marijuana seedlings is a risky and potentially stressful procedure that can slow or even stop growth, and this is especially dangerous for an autoflower.
Make sure the temperature is between 70–73 ºF (21–23 ºC), and pay attention to the amount of water you water with. Remember that different problems can have similar symptoms, so make 100% sure what the problem is before taking drastic measures.
And, of course, look for marijuana seedlings that are healthy and vigorous, not sickly and small.