Rockwool can hold large quantities of water and air that aid root growth and nutrient uptake in hydroponics; the fibrous nature also provides a good mechanical structure to hold the plant stable. It is used primarily for drip hydroponic systems. Rockwool is made by melting a combination of rock and sand and then spinning the mixture to make fibers which are formed into different shapes and sizes.

Rockwool 77 Plug Tray

Tray Dimensions: 53 cm (L) x 31 cm (W) x 3 cm (H).
The tray has 77 Rockwool Plugs in it.
Square Rockwool Plugs (36 mm x 36 mm (Top) x 40 mm (H)

Rockwool has a pH of roughly 7.8. Please see ‘Preparation’ below.


Items you will need

Rockwool plug
Bowl or other container that holds water
pH Balancing Chemicals (pH Down, pH Up)
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.

Hydrate And Stabilize The Rockwool Cubes

Get a bowl or some other container that is big enough to fill with water and have room left for your Rockwool cubes.

Fill the container/bowl with water from your tap.

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.

To accomplish this, use pH down. Add to the water in small increments (a drop), and test the water to see where the pH is. Continue doing this until you have a pH of 5.5-6.

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

Rockwool Cubes are designed to maintain the correct water to air ratio and squeezing them may damage their structure.

Weight 2.054 kg
Dimensions 53 × 31 × 5 cm


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