Why Cannabis Seeds Won't Germinate: Water, Oxygen, Energy and Heat

Every cannabis seed needs four things to germinate: water to wake it up, oxygen to fuel it, the energy stored inside it and steady warmth around 22-25 °C (72-77 °F). Get those right, start with mature, undamaged seeds, and most will crack and show a taproot within 2 to 7 days.

Cannabis seeds need the right conditions to sprout.

Without the right temperature, moisture level or oxygen, they simply won't germinate. 

There are four main factors that drive germination rates in cannabis seeds.

Water

Water is the key player in germination. A cannabis seed's outer shell works as a protective case with a double job: it shields the embryo inside from damage, and it keeps a little stray moisture from kicking off germination too early.

Once the seed is properly soaked, though, it absorbs that moisture and the germination process gets going.

Oxygen

Once water has switched the embryo on, it needs oxygen to start respiring. Oxygen fuels respiration, and respiration unlocks the food reserves stored inside the embryo.

Energy

Through respiration, the embryo burns through those food reserves and produces energy. That energy is what pushes germination forward.

Heat

Even with water, oxygen and energy in place, it's all for nothing without warmth.

As long as your seeds sit at 22-25 °C (72-77 °F) during early germination, they'll push up through the soil and open their first leaves under the sun or your grow lights.

What to check before you germinate cannabis seeds

Damaged seeds

Buying feminized or autoflower seeds from a reputable seed bank, online or in a shop, is the best way to get top-shelf genetics.

Still, check every seed for damage. If the seed is intact, germination should go smoothly.

How old the seeds are

Pro tip: write the date on every seed pack as soon as it arrives. That way you always know how old your seeds are. Like everything else, seeds lose their spark over the years. 

Cannabis seeds can technically stay viable for a very long time, but germination rates drop as they age.

So ideally, germinate seeds that have been stored properly for no more than about 6 months.

Seed color

Cannabis seeds come in different sizes and show various markings on the shell. But color is a great tell for whether a seed is mature.

Light green to pale white seeds are immature and probably won't sprout. So before germinating, make sure your seeds are light to dark brown.

Once a seed has germinated and you can see the taproot, it's time to plant it. That's as easy as poking a hole in your growing medium, dropping the seed in and gently covering it, but plenty of growers mess up that first "watering."

Tip: Don't pour water straight over a freshly planted seed, or you can knock it out of place. Instead, gently moisten the spot with just 1 or 2 tablespoons of water over the thin layer of medium covering the seed. Once the medium is damp, put the seeds under a good light source and keep them warm. In about 48 hours a sprout should break the surface, and you've got a future cannabis plant.

When does a cannabis seed germinate?

A cannabis seed has germinated when it cracks open and pushes out a small root. To get there, it needs the right moisture and temperature. A common method is to soak the seeds in a glass of lukewarm water for 24 hours, then move them to a germination tray or between two damp paper towels and keep them somewhere warm and dark. After a few days they should crack and start growing roots. Keep them moist, and give them light once they've sprouted so the seedlings don't wilt.

One more thing worth clearing up: you can't germinate a bud. Buds are the mature flowers of the plant, not seeds. Seeds form in the female flowers only when they get pollinated, and they're the plant's way of reproducing.

How long does it take a cannabis seed to germinate?

Most cannabis seeds take 2 to 7 days to germinate. How fast depends on a few things: seed quality, temperature, moisture and the germination method you use. Give your seeds the best possible environment, which means a steady, suitable temperature, keeping them moist but not soaked and keeping them out of direct light. Check on them regularly to make sure everything's developing the way it should.