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Germinating Cannabis Seeds in Rockwool for Hydroponics

There are many ways to germinate a cannabis seed, but for germinating cannabis seeds in Rockwool, there are specifics to follow.

  1. Cubes suitable for the growing plant
  2. Ph
  3. Ec
  4. How to germinate the seed

Rockwool Cubes suitable for hydroponics

The most suitable cubes for aeroponic or hydroponics are certainly those made of Rockwool.

These cubes are particularly suitable because they are difficult to attack by mould, have a neutral pH and therefore do not change over time. They have good water intake combined with good oxygenation.

These qualities are very useful when the seed germinates in the cube, welcoming it to an ideal habitat that will help with rooting and proper watering.

To be used optimally, the Rockwool cubes must be soaked in water with a pH of 5.6 for 5 to 6 hours and drained of excess water.

There are many types of systems between hydroponics and aeroponics that require grow cubes. The Rockwool cubes are suitable for everyone because they can be cut with a cutter to give them the shape you want and therefore have a precise adjustment, which is not exactly possible with others such as root, etc.

To cut them, they are taken out of the bath and, after draining, cut with the cutter. You have to be careful, otherwise, they will be damaged or become too dense.

Ph for hydroponic germination

The pH at this stage doesn’t affect much, but once the roots emerge they need an ideal pH.

The cubes must always be rinsed with water at Ph 5.8 with a syringe after bathing with water at Ph 5.6. This pH value must be used and monitored for the entire grow cycle.

If you don’t know what pH is I explain it and also explain how to regulate it in THIS ARTICLE

Ec for hydroponic germination

The Ec at this stage needs to reflect a proper nutrient supply that can be monitored with an Ec meter.

The right Ec should be around 300μS, so almost or no nutrients, just water. The maximum nutrients for germination that can be given are very few. The seed already has the fuel it needs to sprout and grow for its first couple of days.


How to germinate the seed

Regardless of which seed you germinate, the operations to be carried out are always the same.

The best tip for optimal germination is germination greenhouses or humidity domes.

With these greenhouses, an ideal humid habitat is maintained when germinating. A heating mat is placed under the greenhouse, the mat must be connected to a temperature switch so that the temperature remains constant.

It is important that the cubes do not dry too quickly, this is to maintain the proper humidity level of the cube, otherwise, the seed will not germinate.

How to insert the seed

Identify the top of the seed that goes pointed down. From there the root sprouts.


Then take the washed and drained cube, make a 2 cm deep hole with something very thin and insert the seed, point down. You must not cover the hole that was made as the seed will not come out later.

The Rockwool cubes must be placed in a humid environment and have a maximum temperature of 24 degrees.

In addition, the cubes must always remain in the dark. The ideal environment is the constant temperature cabinets

Then take the cubes and put them in the greenhouse after planting. The greenhouse is then placed in a dark cupboard.

Green house/Humidity Dome Maintenance

For optimal germination, the cubes must always be moist and warm when the cubes are cold or too hot, the seed dies. If the cubes are dry, the seed also will not germinate.

The seed can germinate within a couple of days or even up to two weeks. This depends on how long you have had the seeds and what conditions they were stored under. If you know you have old seeds then read this article on germinating old cannabis seeds.

To keep the cube moist, simply wet it with previously prepared water using a syringe. It has a pH of 5.8 and Ec has a maximum of 300-700μS. If you just use ordinary tap water, the seed will germinate also, however, with the recommended technique, root growth will be faster.

Check the cubes twice a day, adding water each time they start to dry out this way. The greenhouse also opens and a little air is changed.

Over time, the seed opens and the root sprouts and expands into the cube. Then the stem lengthens until the first two leaflets, called cotyledons, emerge from the cube.

With this technique, germination is 90% safe, but it may happen that some seeds do not germinate because they are stuck in the cube itself.

To loosen, take a cutter and cut the Rockwool cube in half. Be careful not to touch the seed or the emerged roots and check that the seed isn’t upside down or that the leaves aren’t sticking anywhere, then close it with some aluminum foil.

Once the cotyledon leaves emerge from the cube and turn green, the seedlings can be transferred to the hydroponic system.

Don’t wait for the stems to stretch or they will sag once placed under the lamps.

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