How To Make Rockwool Cubes

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Last Updated on October 30, 2022

Rockwool is a great hydroponic grow media that offers excellent water retention as well as good air circulation. The rockwool cubes are used by hydroponic growers to start their seedlings and root their cuttings. So, if you’re wondering how to make rockwool cubes, we will enlighten you on this.

It is one thing to buy ready-made rockwool plugs or starter cubes but do you know you can make some of these rockwool yourself? Making rockwool cubes will even cost lesser thereby saving you more. You also get more numbers of cubes at a lesser price.

So, if you wish to learn how to make rockwool cubes for growing, read on to learn about this.

Rockwool Cubes

Rockwool is a natural product with a thick mat that comprises a long strand of natural fibers. They are formed by melting (at a very high temperature of 3000 degrees Fahrenheit) the combination of chalk and basalt rock to form lava. This lava is then tossed into a spinning chamber which forms the fibers that look like cotton candy.

After spinning the fibers, a binding agent is used to mix and press them into bigger mats or slabs. It is these mats that are cut into different sizes and used as growing mediums in hydroponic systems.

Rockwool Cubes

So, because of this firing process, these rockwool cubes are biologically and chemically inert. This makes them a perfect growing medium for your hydroponics systems.

Rockwool cubes are very efficient as grow medium because they will retain good moisture and also retain oxygen. This is essential for germinating seeds as well as cuttings for propagation. They are also used to grow various compact plants.

Learn How To Make Rockwool Cubes

Making your rockwool cube is a great idea to save up from excess cost. To make rockwool cubes, you need to obtain rockwool slabs. You can obtain them from large construction companies that buy in bulk and use them to your advantage as an indoor grower. You can also check any hydroponic supplies store for these slabs.

Rockwool Growing Slabs

Obtaining rockwool slabs will cost you lesser at the same time gives you plenty numbers of rockwool cubes to be used for planting. You can get almost 200 rockwool cubes from one rockwool slabs and they can be used for growing in rockwool slabs.

So, after obtaining your rockwool slabs, pick one and make a cut along the middle length of the slab with a sharp knife or tool. Now that your slab has been cut into two, go ahead and cut them further into cubes. Cut the cubes according to the shapes you want.

Learn How To Make Rockwool Cubes

Once you’re done cutting the cubes, go ahead and soak and drain them in preparation of seed planting. You will need to make small holes or incision on the top of your rockwool grow cubes. This is to create the hole for your seed to be placed in. Then you go ahead and place your seeds into the holes for germination.

Note: ensure you wear gloves and put a mask on while making or handling these slabs. Their dust or tiny fibers can become airborne and it’s important you prevent them from getting into your respiratory system.

Benefits Of Using Rockwool Cubes

There are many benefits to suing rockwool and they include:

  • Water Retention & Draining: Rockwool cubes are well-draining and overwatering issue is less likely to occur. At the same time, they will retain a good amount of water for your plant growing needs.
  • Air Circulation: they also allow adequate air to circulate thereby oxygenating the plant roots.
  • Reusable: Because they are derived from rock, they are less likely to degrade. Therefore, you can use them many times.
  • Sterile & Safe: They are very sterile and contain no pests or pathogens and they are free of weeds. They are also safe to use as they don’t contain any harmful chemicals.

1.5″ Rockwool Starter Plugs, 2 Sheets of 49 Plugs

How To Prepare Rockwool Cubes

Rockwool cubes preparation is an important step to take when using these cubes. Because of the manner in which they are made or manufactured, unprepared rockwool cubes have a very high pH. There is presence of lime in abundance in the rockwool fibers which increases the pH and the pH is usually around 8.

With this high pH, if used in your hydroponic system unprepared, they can cause nutrient lockout thereby causing a nutrient deficiency. Plants majorly do well in slightly acidic mediums. Therefore, lowering the pH of your rockwool cube is required.

Rockwool Grow Preparations

A good way of preparing rockwool cubes for the purpose of lowering their pH is by soaking them in acidic water. This acidic water will dissolve the lime present in the rockwool fibers thereby lowering the pH to an appropriate range.

Distilled water will do just fine because of its purity. However, you can also make use of tap water if that’s what you have available.

When reducing the pH of your rockwool, ensure you do it slowly while testing the Ph level at the same time. You want to attain a pH level of 5.5 and nothing lower than 5.0. Make sure the pH does not go down below 5.0. This is so you don’t destroy the rockwool fibers when it gets too acidic.

The rockwool cube should be immersed in water and allowed to soak for up to 24 hours. Once you’re done soaking. Take them out of the water and gently place them into your hydroponics system. With the prepared rockwool in your system, let your hydroponics system run without any plants.

Do this and wait until the pH of your hydroponic system reaches 5.0 to 6.0 ranges. This shows that the rockwool cube is stable and are ready for planting.


What is rockwool for plants made of?

Rockwool is a natural, organic material that is formed when water seeps into the cracks in stone. Over time, these stones turn into hard, porous rock with the consistency of cheese. The rockwool is collected from the quarry and processed to remove impurities. What is rockwool used for? Rockwool is one of the most popular growing media because it provides many benefits for plants.

It’s a great choice for high-light and low-light environments, and it can be used indoors or out. Rockwool also provides air and moisture circulation, as well as good drainage. It’s an ideal growing medium for houseplants because it absorbs water, helps prevent soil from drying out, and is perfect for retaining water.

Rockwool comes in several different shapes, sizes, and textures. The best types for houseplants are pebble, granule, and cube. 

How do you prepare composting with rock wool cubes?

The following is how to prepare rockwool cubes to help you get your compost started.

Step 1: Collect your material

If you want to use rockwool cubes to start your compost, you will need to collect a wide range of materials. This includes organic waste that you normally throw out, such as food scraps, paper, leaves, grass clippings, and weeds. It also includes animal manure that you have collected, such as chicken, horse, cow, or rabbit manure.

Step 2:Remove the packaging

If you are using rockwool cubes to start your compost, you should remove the packaging before placing it in the pile. This includes removing any labels that might say “do not compost” or “biodegradable only.” It also includes removing any plastic wrapping that you might have put around the rockwool cubes. You should remove this wrapping before putting the cubes into the pile.

Step 3: Place the cubes in the pile

If you want to use rockwool cubes to start your compost, you will need to place the cubes in the pile. When you are ready to do this, first make sure that the material that you collected is dry enough to make a good compost. Then, simply place the rockwool cubes into the pile and cover them with an additional layer of the material that you collected.

Step 4: Start turning the pile

If you want to use rockwool cubes to start your compost, you will need to start turning the pile. This means that you will need to periodically turn the pile by lifting the material and turning it over. This will help to expose more of the rockswool cubes to air and light. You should keep turning the pile until the material is completely dry.

Step 5: Water Your Composting

Compost can be water-logged if there is too much moisture in it, which can lead to problems like mold or rotting. To prevent this from happening, you need to keep your compost moist. This means that you should add water when you add the materials. You should then water the pile regularly. This will help to keep the compost healthy. When you want to use a compost bin, you can start using one right away.

Final Say On How To Make Rockwool Cube

Rockwool cubes are one favorite grow medium amongst hydroponic growers and they are available in different sizes and shapes. They are safe to use and they will provide your seeds or plants the basic features to grow optimally.

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