Grow Guide: How to Start Cannabis from Seed
Starting cannabis from seed is an affordable and fulfilling way to start growing. It all starts with germinating cannabis seeds, followed by creating the ideal warm, humid environment for seedling growth.
Giving your seeds (and then the seedings) the best support from the very start, you’ll set yourself up for success come harvest. Here are the basics to growing cannabis from seeds.
Where to Find Cannabis Seeds
At this point, there are hundreds of different online options for sourcing cannabis seeds . If you are growing indoors, the world is your oyster, as many websites are willing to ship nationally (or even internationally). Plus, if you master the indoor environment, you can recreate perfect conditions for even the most demanding of strains.
For those growing outdoors, try to locate a local breeder who also cultivates outside. These cultivars will be adapted to your unique climate and will likely produce better results.
No idea where to start? Seed Finder is an excellent resource for sourcing specific genetics and breeders in your area. But this is just one place among many in today’s weed-friendly world.
How to Germinate Cannabis Seeds
What You’ll Need:
- Cannabis seeds
- Paper towel
- Plate or tray
- Ziplock bag
- Heating mat (optional)
The first step to growing cannabis from seed is learning how to germinate them. Place cannabis seeds on a sheet of paper towel, laid on top of a tray. Dampen the towel with water so it’s wet but not soaking.
Fold the towel in half to cover the seeds, and enclose it inside a Ziploc bag. Place the entire tray on a heating mat, the top of a fridge or other warm area of your house. Cannabis seeds germinate between 71 to 77°F (22–25°C).
Check back every day for signs of life. If your seeds are viable, they should sprout within a week. If you are still waiting for a few to emerge after a week, toss those and begin again. If no seeds have sprouted, your seeds are no longer viable.
Ed Rosenthal recommends soaking seeds for 12 hours before germination. His formula uses water, a cannabis rooting solution and hydrogen peroxide.
This solution is a good option for commercial and large scale growers, as it reduces the risk of fungal infection and encourages rapid sprouting. Compost tea is another excellent option for a natural alternative.
Ideal Conditions for Cannabis Seeds and Seedlings
What You’ll Need:
- Germinated Cannabis Seeds
- Potting Mix (or Root Riot Plant Cubes )
- Propagation Tray with Dome
Once germinated, you must carefully move these tiny seeds into the soil or soilless growing medium like Root Riot Plant Cubes. When you start cannabis from seed, the aim is a warm and relatively humid environment.
Starting Cannabis With Soil
If using soil, choose an organic potting mix suitable for seeds and starts. Water soil mixture before use, and fill potting containers that have a drainage hole. Avoid pellets that are commonly sold at garden centers, as they don’t retain moisture well, and it’s challenging for cannabis roots to break free of the netting.
Using a popsicle stick, tweezers or a toothpick, lower the germinated seed into a premade hole roughly two the three times the height of the seed. As you gently fill in the hole, be careful not to damage the sprout.
Starting Cannabis for Hydroponics
For hydroponics, you’ll want to use Rockwool cubes or Root Riot Plant Cubes. These come pre-cut into perfect starter plugs, often with a hole in the middle for the seed.
Before use, soak the cubes in water and rooting solution until they are wet but not dripping. Gently lower the germinated seed into the hole using a popsicle stick, tweezers or a toothpick. Be extremely careful not to damage the early sprout.
Whatever option you choose, keep the seedlings at a consistent temperature: 68 to 77°F (20 to 25°C). Depending on where you live, a heating mat may be necessary. Use a propagation tray with a clear dome to trap the humidity in, but open up once a day to encourage a bit of airflow.
Lighting Requirements for Cannabis Seedlings (& How to Eliminate Stretch)
Seedlings and starts require 16 hours of light a day and eight hours of dark. You can even bump this up to 24 hours a day, and the seedlings will continue to eat it up.
What kind of grow light do you need for this early stage of development? Not the same capacity you’ll need for veg and bloom. Higher wattage types of HID lights (Metal Halide and High-Pressure Sodium) are far too powerful for sensitive seedlings.
Most growers use a simple LED grow light or a CFL fixture. Ed Rosenthal recommends 40 to 60 watts per square foot.
While these may not be entirely enough for veg and bloom, they produce enough light for seedlings without the added heat. This means you can place the lights close to the tops of the seedlings.
Place lights as close as possible to the tops of the starts, without raising the temperature over 77°F. You want seedlings to get enough light without burning them.
The goal is to avoid early stretching in your small cannabis seedlings. Healthy seedlings are short and wide, not tall and skinny. Stretching is when the sprout reaches tall for the light without putting out leaves.
Typically, under outdoor conditions, plants remain short for the first few weeks as they focus energy on building structure and root development. Stretching inside demonstrates the seedling is not getting enough light. The light source is either not intense enough or too far away.
When to Transplant Cannabis Seedlings
The primary goal for starting cannabis seeds in small pots is to encourage healthy and strong root development. Once the seedling has three to four sets of leaves, begin checking root development. This will likely be three or more weeks after germination.
Another telltale sign it’s time to transplant is when you notice roots begin to creep out from the drainage holes. If working with Rockwool, a key indicator it’s time to transplant is when the roots begin to outgrow the cube. A plant’s growth trajectory slows down if it is root-bound. If the roots have consumed the available space, it’s time to move up a size.
Cannabis Seedlings From Germination to Transplanting
Starting cannabis from seed gives growers access to a much larger genetic pool than what you can find locally from a clone supplier. Plus, if you’ve got the time to invest, it’s a much more affordable way to grow cannabis. Finally, if you are already set up with a veg and bloom room, you have everything you need to get started from seed.
Fail-Proof Guide to Germinating Seeds in Hydroponics
Plus, How to Care for Hydroponic Seedlings…
We have a cannabis seedling germination page which has everything you need to know about all the different germination methods, but this tutorial is different. In this hydroponic seedling tutorial I’m going to share exactly how I do my seeds from beginning to end in a DWC/bubbleponics setup!
Just follow these instructions and you’ll end up with healthy, fast-growing plants that germinate in just a few days. It’s pretty much fail proof!
Learn How to Start Seedlings So You Can Grow Hydroponic Cannabis Plants Like This!
1.) Get Cannabis Seeds
There are a few different ways to get cannabis seeds, with the most common being ordering seeds online and growing seeds you find in weed that you buy. Learn how to research and find the right strain.
Here’s a picture showing several healthy and viable cannabis seeds
2.) Germination for Hydroponics
I’ve tried a bunch of different germination methods over the years, and the technique I prefer is for hydroponics is starting with the “Paper towel method” to germinate, putting the germinated seeds into Rapid Rooters, and installing the Rapid Rooters directly into reservoir. Lots of other germination methods as well, but this has worked best for me!
Paper Towel Method
This method is hard to mess up if you follow the instructions!
- Place your seeds inside a folded wet paper towel, and place it between two paper plates (or regular plates) so that they don’t dry out.
- Check on your seeds every 12 hours but try not to disturb them. When they’ve germinated, you’ll see the seeds have cracked and there are little white roots coming out.
- They should germinate in 1-4 days, though some seeds can take a week or longer (especially older seeds).
- Keep them warm if possible. One thing you can do to get seeds to germinate a little faster is to keep them in a warm place (75-80°F). Some people use a seedling heat mat but in most cases that’s unnecessary.
These seedlings were sprouted using the paper towel method!
3.) Place Germinated Seed in a Rapid Rooter
The Rapid Rooter should be cut open lengthwise
Gently place the germinated seed inside, root down
Most seedling plugs will go back into place easily, and you’ll barely be able to tell it’s been opened
4.) Prepare Hydro System for Its New Guest
If you haven’t put your hydroponic system together yet, now is the time! Make sure your pumps are all running, and that you’ve made a reservoir with seedling-strength nutrients. You need a home to put your new plants!
Hydro Tips & Hints
- Air bubbles – have lots and lots of bubbles in your water reservoir. That means your air pump needs to be on all the time for the full grow. The main benefit of hydro is your plant roots are getting an unlimited amount of both water and oxygen. This is achieved by dissolving a lot of air into the water via an air stone and air pump. In order to get the fast growth, you want a lot of bubbles! A highly-oxygenated tank is also far less likely to get root rot, or suffer from other unwanted organisms growing in the reservoir! – This supplement contains a specific bacteria that was first found in rice paddies in Japan in the 40s! It’s been common in Asia for years but only in the last several years has it been available in the US from a company called Botanicare. I highly recommend, even insist, that all hydro growers get this cheap-but-effective supplement to keep plant roots healthy!
- Add seedling level nutrients from the beginning. A lot of growers, especially soil growers, will tell you not to add any nutrients for the first few weeks of the plant’s life. That makes a lot of sense in soil, because there are lots of nutrients contained in the soil itself for your young cannabis seedling, and giving more right at the beginning can end up giving way too much for such a young plant. However, in hydro, the only nutrients your seedling gets is what’s in the water, plus what little was contained in the seed itself. Because of that, I highly recommend giving seedling-strength nutrients to your plants from when you first fill your reservoir. Seedlings grow a LOT faster with light levels of nutrients than if you only give plain, pH’ed water at first. from the beginning of your plant’s life to end the of your plant’s life
5.) Install Rapid Rooter and water the seedlings until roots reach the water reservoir – Turn on light to keep seedlings warm for best results!
Make sure to always keep the Rapid Rooter moist but not soaking wet.
If you have a top-feed, place the tube near the bottom of the net pot so the water isn’t soaking the seedling’s roots. You just want water dripping out the bottom so the root can use it for oxygen and water until it’s fully established in the reservoir.
Add your Rapid Rooter(s), and fill around the edges with extra clay pellets to hold each one in place.
Since your seed has already sprouted and been in placed into the right growing position, it’ll often pop its head out within just 12-24 hours! Sometimes you see just the leaves, but occasionally you actually see the seedling push the shell above ground. I keep the grow light on even before the seedling appears. It helps keep it warm and guide it toward the light.
When this happens the shell usually falls off on its own as the seedling grows!
The Rapid Rooter in this picture is a little too wet, which makes the seedling prone to “damping off.” If you ever notice the Rapid Rooter actually looks wet or shiny, it’s too much water. Try turning the top-feed off every few hours, or hand-watering the seedling at first. Too much moisture can kill!
Don’t use a humidity dome on seedlings unless it’s very dry where you live. If you do use a dome, consider keeping a vent open and watching the humidity. A young seedling doesn’t require high humidity, and they tend to get “wet feet” and stop growing in constantly wet conditions.
Now that your seedling in in the tank, it’s time to learn how to….
6.) Take Care of Hydro Seedlings
Here are tips for taking the best care of hydroponic marijuana seedlings:
- Leave roots alone as much as you can with young seedlings in a hydroponic setup. It takes them a little while to get all established in the tank, almost like a fish, and during that time seedlings are much more sensitive to their roots being touched or being moved around. If at all possible, try to let the seedling grow in the same place without being moved for at least a few weeks until you put them in their final home, or even just start them in their final home!
- Avoid reservoir changes for a few weeks if you can – Going along with what I said before about leaving the roots alone, I’ve found that young seedlings often don’t respond well to reservoir changes. Instead of changing the reservoir, just top off with half-strength vegetative nutrient water until the plant is at least 3 weeks old. It won’t be using enough nutrients to mess with the ratios, and as long as you maintain the pH and use Hydroguard your young plant will be fine with being topped off.
- Check the pH dailyto prevent nutrient deficiencies
- Warm but not hot temperature– I recommend hydro growers aim for 75°F, and try to stay between 73-80°F.
These seedlings are a few weeks old, and the grower plans to move them all to the
This is a time-lapse video of a cannabis seedling sprouting and growing over 13 days.
Cannabis seedlings just getting their bearings – try to avoid moving or disturbing them until they are growing fast, with new leaves every day!
Big cannabis plants ready to switch to the flowering stage
I thought hydro plants liked it cold?
Just like in soil, cannabis plants in hydro tend to grow faster in relatively warm temperatures. This is a somewhat controversial statement because a lot of hydro growers prefer to keep their temperature lower in the grow space to help prevent root rot. In fact, there are some growers right now who are reading this and shaking their heads at me.
There’s good reason to believe that hydro plants would grow better with a cool reservoir. For example, the bad microorganisms that make root rot don’t survive well at lower temperatures. Additionally, water can physically hold more oxygen at lower temperatures, which seems like it would be great for faster plant growth. Because of this, lots of growers will AC their room to 60°F, and/or get a water chiller to cool their water reservoir to a similar temperature.
I do agree that if the temperature is above 80°F, your plant is a lot more likely to get root rot. However, I personally have not found that cool temperatures are adequate to prevent root rot. Even if the temperature is 60°F, you still need lots of bubbles and a “good bacteria” supplement like Hydroguard to prevent root rot in many cases.
I’ve seen several growers buy a water chiller and still get root rot. So I personally don’t believe cold temperatures are the best way to go to keep roots healthy.
The other reason I recommend to keep it warmer is because the plants just grow faster around 75°F in hydro. If your roots go from 60°F to 75°F, you’ll see the plants start growing faster in just a day or two, just like how plants in soil grow faster when it’s warm!
Just like in soil or coco, cannabis plants in hydro grow fastest when it’s a little warm, around 75°F!
Although there may be more oxygen dissolved in the water at lower temperatures, at least in my grow tent that apparently isn’t the limiting factor to growth, because plant growth speeds up at warmer temperatures.
I’ve found that if the grow space feels cool to you, it also feels cool to your plant most likely, and it may not be growing to its full potential. Some Sativa strains are particularly sensitive to the cold, though some Indica strains from cold climates will still thrive at lower temps.
Autopsy: Why Aren’t My Seeds Sprouting?
If your seeds still aren’t sprouting and growing properly, consider the following factors.
If there’s no germination at all…
- Temperature may be too hot or cold – aim for 75-80°F
- Too wet – seeds and seedling roots should always be moist, but should not stay wet
- Too dry – if a root dries out the seedling can die!
- Bad seeds – It might not be you, it could be the seeds themselves! How can I tell if seeds are viable?
If seeds sprout, but then stop growing…
- Temperature is too hot or cold – aim for 73-78°F
- Too wet – even though your plants are growing with root directly in water, new seedlings don’t like “wet feet”. They don’t like for it to be too wet near the seed for too long, so make sure your Rapid Rooter or growing medium nevers looks shiny or muddy, as that means there’s too much water! Young roots that stay too wet for too long start to get mushy and die. For this reason, it’s also usually recommended to avoid using a humidity dome with seedlings unless your air is dry. Although clones love humidity domes (they need water from the air because they don’t have any roots to get water), seedlings like it a little more dry or roots tend to get mushy.
- Too dry – less common unless you live in a very dry area, but sometimes your medium dries out too fast if you’ve got a heavy-drinking, fast-growing seedling!
- Too much light – if the seedlings get blasted with high levels of light right away, it can shock them. They may need some time to adjust to higher light levels. Simply starting your grow light a little further away that normal is usually enough.Think sunny window at first, and start ramping up after a week of healthy growth.
- Not enough light – if seedlings are growing long and stretchy without growing new sets of leaves, it means it wants more light.
- No light for more than a day – if the sprouted seed doesn’t get light within 24 hours after sprouting, it may die. Once seeds are sprouted, get them in a Rapid Rooter and under at least some amount of light as soon as possible!
- Roots damaged – If somehow your roots got damaged, it can sometimes stop the seedling from growing
Unfortunately sometimes you will never know why certain seeds just don’t thrive! It’s all part of nature
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