Can You Use Rockwool Insulation For Hydroponics?

There a lot of areas around the world where hydroponic Rockwool cubes are super expensive or even unavailable. This made me wonder, can I use rockwool insulation as an alternative for the traditional hydroponic rockwool cubes?

So, can I use rockwool insulation for hydroponics? Rockwool insulation is made of fibrous material just like that used for hydroponic rockwool. So, the short answer is yes, it can be used to grow hydroponic crops. However, rockwool insulation is pretreated with various chemicals that can be harmful to your hydroponic plants.

There are a huge number of growers who decided to shift lately and use alternatives like rockwool insulation for their hydroponic systems. A shift like this is hugely a result of several things.

Hydroponic rockwool cubes do cost a significant amount of money in some areas of the world. In India for example, 100 cubes of hydroponic rockwool cost around $30 while in the USA, it costs only $15 to get the same 100 hydroponic rockwool cubes.

In countries like Pakistan, hydroponic rockwool is not available 90% of the time. So, it would make a lot more sense to use other locally available alternatives.

Another group of people has chosen to use insulation rockwool because of its availability. Their direction would be usually to bootstrap their whole hydroponic system from materials present at home.

The Difference Between Hydroponic Rockwool And Insulation Rockwool

There are a lot of differences between hydroponic and insulation rockwool cubes. These differences are critical enough that in some cases, it might lead to the plant’s death, so we have to bear in mind that insulation rockwool has its disadvantages.

The Dangerous Chemical Ingredients In Insulation Rockwool

Insulation rockwool is treated with chemicals and additives to make it fireproof. These chemicals are extremely dangerous when it accumulates during the lifespan of any hydroponic plant. On the other hand, hydroponic rockwool cubes are not pre-treated with these chemicals because simply, there is no need for them.


Formaldehyde binder is a chemical that is added during the production of insulation rockwool. Most of the formaldehyde in the rockwool is eleminated before the end of the production phase. However, there are some traces that do remain in the end.

These traces do accumulate, especially if you are trying to grow more than one plant using several rockwool cubes in one hydroponic system. According to several studies, formaldehyde has shown to decrease the wet weight of the plant by 27%. Moreover, the plant’s water content has decreased by 5% as well.

If you intend to use a large number of insulation rockwool cubes, then you have to take into consideration that excessive exposure to formaldehyde traces can cause irritation to the eyes, nose, and throat.


Some rockwool cubes do contain asbestos. According to the World Health Organization (WHO), asbestos do contribute to about half of the deaths of occupational cancer worldwide.

Asbestos was banned from being used in almost all products since the 1980s. However, in some third world countries like India and Pakistan, you can still expect to find asbestos in some insulation rockwool products.

Studies have shown that plants grown in high concentrations of asbestos tend to show lower levels of nutrients in leaves. Moreover, an overall decrease in growth rate was present.

So, as you can see, asbestos can be super harmful to both humans and plants.

Insulation Rockwool Effect on Root Growth

Insulation rockwool tends to be more compressed than hydroponic rockwool. When the seedling’s roots are growing during the early stages, they will be met with huge resistance as a result of how tightly packed the mineral wool is.

So, don’t expect to get the same growth rate of hydroponic rockwool cubes from insulation rockwool as there are huge differences in their core structure. Moreover, some seeds will not even going to make it past the germination stage as a result of the difficult environmental conditions.

After all of the previously mentioned problems, you have two options to choose from. You can use coco coir as a growing medium instead of an insulation rockwool. Coco coir is present in many countries where there is an absence of hydroponic rockwool. So, it can be a great alternative to choose from.

Another option is that you can still use insulation rockwool as a growing medium. However, you must treat it first before starting to use it for your hydroponic plants.

How To Treat Insulation Rockwool Before Using It For Hydroponics

If your back is against the wall like many growers, and the only option for you is to use insulation rockwool as a growing medium for your hydroponic system, then you have got to follow these steps carefully in order to avoid the negative side effects that might occur to your plants.

All of the following steps will significantly impact the cubes. So, you have to be careful when you are trying to plant the seeds and to bear in mind that their structural integrity can never return as before. However, they can still be used to grow your hydroponic plants.

1-Dish Washer Detergent

In order to remove the chemicals that the insulation rockwool was treated with, you will have to soak it in a dish washer detergent of any type for up to 24 hours.

2-Hydrogen Peroxide

This step is meant to be done when you are planning to reuse the rockwool cubes of your last growing batch for the next seedlings. It is done to clean the rockwool cubes as much as possible. Moreover, it will eliminate the transmission of any type of disease from the old batch to the new one.

After removing the insulation rockwool cubes from the dishwasher detergent, you should soak the cubes in hydrogen peroxide for additional 24 hours.


Then comes the important part, which is soaking the rockwool cubes in water. One of the main features of rockwool cubes is it’s great ability in attracting and retaining moisture.

If you started to germinate seeds in dry rockwool cubes, all of the moisture will be attracted and retained inside the cubes with little to no moisture reaching the seeds. Therefore, there is a thin chance that your seed will germinated from the first place.

Instead, we should soak the rockwool cubes in water until there are no air bubbles coming out to the water surface anymore. By doing it this way, we ensure that all of the moisture will reach the seeds and allow them to germinate and become seedlings.

4-Adjusting The pH

Generally, rockwool cubes tend to have higher pH levels when compared to other growing mediums. This can result in messing up your nutrient solution pH after originally setting it up.

So make sure to check and regulate the nutrient solution pH after adding the rockwool cubes to your system.

In some cases where you are still in the early stages of germination and there is still no nutrient solution for the seeds. You can soak the rockwool cubes in a solution with the optimum pH of the seeds that you are trying to grow.


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