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.

If you prefer visual content check out our YouTube channel here.

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.

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. 

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. 

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. 

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. 

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. 

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.

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.