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starting marijuana seeds in rockwool

When your seedlings/cuttings have outgrown their blocks, you’ll need to move them into your hydroponic setup. Before we explain how to do this, here are the best and most suitable systems to use alongside Rockwool blocks.

However, if you’re trying to grow cannabis as cheaply as possible, you can probably squeeze another plant or two out of the same Rockwool cube. First, you’ll need to submerge it in boiling water to kill off lurking pathogens dislodged from the previous root system.

Rockwool cubes are sterile and inorganic. After being exposed to extreme heat, Rockwool arrives at a grower’s doorstep clean and ready for use. Because it doesn’t contain any organic matter, Rockwool helps to protect the root zone against damaging microbes.

Seeds (Soil)

Upon mimicking a volcano, the factory machinery then needs to mimic the wind. The lava enters a spinning machine that whips it into thin strands of stone wool. The addition of some binding solution oil helps to hold the strands together. Another machine layers several sheets of wool on top of each other, then a conveyor belt passes them through a series of rollers that compress the wool into a dense mat and improve its structure.

Rockwool cubes are naturally alkaline. Because cannabis plants prefer slightly acidic soil, growers have to stabilise the pH of their cubes before sowing seeds (you’ll find out how to do this below).

Sometimes seeds struggle to become established when sown in compact and hard soils. However, they establish themselves quickly and easily within Rockwool cubes. The young roots easily pass through the gaps between the fibres.

Some growers like to keep repotting their plants as they grow. However, for the sake of simplicity, we recommend transplanting into a fabric pot and keeping your plants there until harvest. This reduces future transplant stress and keeps plants growing quickly.

3 days. Once the first true leaves emerge, we want to select for the strongest one (the one that grew the tallest), and cut off the tops of all other seeds that are growing next to it. Do not pluck them out, as you may uproot it’s neighbors. Simply cut it off as close to the hole as you can without messing with the stronger one that you plan on keeping alive.

Using either a PH test kit or a Ph meter, determine the Ph of the water. Water comes out pretty alkaline, usually around 7.4, so you will need to acidify it a little bit to bring that Ph down to the desired level. Aim for as close to a Ph of 5.5-6 as you can get.

Now that we have the Ph adjusted water, it’s time to stabilize and hydrate the Rockwool cubes in it. Insert the Rockwool Cubes into your container and let them soak for roughly 1 hour. Once the hour is up, the cubes will be big and fat with water. Take them out of the bowl of water and put them somewhere you don’t mind getting a little wet. Save the remaining water for step 3.

Important: Do not let the PH of the water go below 5. A Ph this low will damage the fibers of the Rockwool Cube

Rockwool Cubes have a PH of roughly 7.8. This is pretty alkaline, yet our plants prefer to grow in a slightly more acidic environment (between 5.5 – 6.5). In order to prepare our Rockwell cubes for the seeds, we need to soak them in some PH adjusted water, that way they have everything the seeds need to germinate and sprout; water and a slightly acidic environment.

Most Rockwool cubes come with holes in them, if yours did not, than create a hole in one side that is approximately a quarter inch (0.75 cm) deep.

Rockwool Cubes are designed to maintain the correct water to air ratio and squeezing them may damage their structure. Some of the marijuana forums advocate doing everything from squeezing them completely dry, all the way to flinging them around like paintbrushes in order to get excess water out. None of that is necessary, leave it as it is. It will stay moist for several days without needing to be watered this way as well.

Some people claim they use a diluted nutrient solution to water their Rockwool cubes with during germination. Do not do this, as my experience has always been negative. Note the picture below, where I did an experiment by adding a very diluted grow nutrient to the Rockwool cube on the far left. It died within an hour or two, and the others went on to live happy lives. In my opinion, they do not need nutrients until they get into your hydro system.

Now that we have the Ph adjusted water, it’s time to stabilize and hydrate the Rockwool cubes in it. Insert the Rockwool Cubes into your container and let them soak for roughly 1 hour. Once the hour is up, the cubes will be big and fat with water. Take them out of the bowl of water and put them somewhere you don’t mind getting a little wet. Save the remaining water for step 3.

Check out this method in action:

Step 1: Hydrate And Stabilize The Rockwool Cubes

But the best way to germinate weed seeds would really be a combination of these methods.

Not all of these methods have the same success rate, and your precious cannabis seeds are expensive to buy.

Fill the container/bowl with water from your tap. You may also choose to use water filtered through a britta or reverse osmosis (R/O) water, I’ve had success with all 3 of them so whichever you have on hand will work fine.