Germinating cannabis seeds in rockwool

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Germinating cannabis seeds in rockwool

Germinating cannabis seeds in rockwoolGerminating cannabis seeds in rockwool, Rockwool is a great substitute for soil, especially for germinating your Cannabis seeds.

I would suggest only to germinate one seed in each rock wool cube.

First you should find a small but sharp kitchen knife to make two little incisions in a dry rockwool cube forming an X, about 1 cm deep.

cut open piece of rockwool
This cut open piece of rockwool shows how the root inside develops during the seedling stage of your Cannabis plant.

Carefully place one seed in the incision about one centimeter deep.

When the seed is inside the rockwool you should soak it with tap water at room temperature untill it is fully saturated.

Now you should place the rockwool inside a propagator and keep it at a nice temperature of around 21 degrees Celsius.

If you can not get hold of a propagator, you can make one by wrapping some cling-film around a container big enough to comfortably hold the rockwool and at least twice as high.

A propagator will create a perfect micro-climate with a very high humidity which stimulates root growth in your young Cannabis plants, if you place a light directly above it you will automatically increase the temperature inside the propagator.


Every plant should be individually labelled,
Every plant should be individually labelled, especially when growing multiple strains.

There are a lot of propagators available, some of the better ones come with build in temperature control

Your seeds will need at least 18 hours of sufficient and un-interupted light.

This could be any type of light that is not too intense, a fluorescent tube or any other regular household bulb will do the job, as long as they are reasonably close (1-3 foot) above your propagator.


Place the rockwool in a small pot, filled to the half with seedling soil.
Place the rockwool in a small pot, filled to the half with seedling soil.

As soon as the seedling becomes visible above the rockwool, it comes in direct contact with light and will start its pre-vegetative cycle.

As soon as the seed grows out of the rockwool you will need to transplant it to a pot with soil as soon as possible.

Before you can transplant your seedling you need to prepare your pots and label them.

Make sure every plant/pot is individually labeled, this will create a much more organized workflow and prevent mix-up’s.

I like to use 10 cm wide, square pots for my seedlings, you could use a smaller pot but I would not recommend a larger pot.

You should always use a bottom tray or propagator to place the pots in, these will catch and hold the excess water from your pots.


fill the pot with more seedling soil.
fill the pot with more seedling soil.

Fill the pots to about half their height with seedling soil and compress it slightly with your hand, now gently add some water without disturbing the top of the soil.

When the soil is wet you can take the rockwool with the seedling and place it on top of the soil and fill the remainder of the pot until the soil reaches about 1 cm from the top.

Press the soil firmly with your hands to tighten the soil around the rockwool cube and add more soil if needed.

Once again add enough water to soaken the soil and place the pot in your propagator or straight under some fluorescent or T5 grow lights and provide them with 18 hours of light every day.

Your Cannabis plants have now entered their pre-vegetative cycle.



Propagators create the perfect climate
Propagators create the perfect climate for your seedlings and germinating plants.

More germination tips in Germinating cannabis seeds in water



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  1. Hi Heath

    When I germinate in rockwool I usually soake the cube first and then I’ll take one of those china chopsticks and hold it between thunb and forefinger and then “roll” a hole about 1 cm deep as you say and then put the seed in, after that I’ll take a itsy bitsy tiny piece of rockwool from the side of the cube and gently with the tip of the chopstick fit it in the little hole,applying a bit of pressure to close the hole, the rest of the way is spot on what you’ve said.

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