Rockwool is one of the most popular mediums for hydroponic growing. It is easy to use, cost effective, and inert which keeps it from going rancid. Rockwool also goes by the names mineral wool or stone wool as well because it is made using molten, superheated rock that is then spun in a similar way to wool.


This material was originally designed to be a form of insulation for homes and buildings. The natural air pockets contained in the medium are perfect for adding insulation value and is cheap to make. Rockwool is also inert, which means that there is nothing for organisms such as bacteria and fungi to feed on. This allows them to last for many many years, and resist rotting. These qualities also make for a perfect growing medium conditions, which eventually led to the incorporation of rockwool into hydroponics.

Today, rockwool is the first choice for large and small scale growers alike, and can be used on any type of crop. Find high quality rockwool here.

Rockwool is the perfect medium for beginners because it is incredibly easy to get the water to air balance right. As long at the rockwool is kept moist, without being overly soggy or submerged in water, the rockwool promotes a nearly perfect air to water ratio all on its own.

Beginners are not the only ones benefiting from this ease of practice however, many large scale commercial growers choose to grow using rockwool due to the low cost, and ease of use. It allows for a higher success rate with their plants, even with inexperienced staff members, and is cheap enough to justify having the entire substrate discarded after each grow in order to reduce the chances of disease or pest infestation.

The Positives and Negatives of Rockwool:


  • Highly cost effective
  • Allows the grower to move plants around or between different setups
  • Maintains a nearly perfect air to water ratio
  • Accommodates plants during all stages of development, from seedling/cutting, to harvest
  • Will not rot or go rancid
  • Allows a water buffer for the plants roots to keep them from drying out as quickly
  • Lightweight and stores for many decades


  • The substrate should be discarded after each grow
  • Algae can buildup on the top of the moist rockwool cubes
  • Some systems such as DWC or Aeroponics is not suitable for use with rockwool 

How to grow using rockwool

1. Soak

It’s important to soak the rockwool for at least 30 mins before use to allow the rockwool to hydrate completely. Many growers add buffer agents at this point as well to bring the pH closer to optimal range. Getting the water to a pH of 5.5 before soaking will yield the best results.

Some choose to also add nutrients to this water in order for it to allow the rockwool to have an even distribution of nutrients. We recommend not using nutrients for seedlings or cuttings however, until they have a fairly developed root system. If you do want to use nutrients for these plants, start with only 25% the recommended dosage, and work up to 100% over the course of 4-6 weeks as the plant develops.

2. Place the rockwool into your system

Now that the rockwool has had a chance to soak, remove it from the water and allow it to drain off, do not squeeze the rockwool though! You only want the excess water to drain off.

Place this rockwool into your setup. This can be as simple as a tray or simple propagator, into an EBB and flood system, or into pots. The most common application of rockwool by far is to use a drip system. With a drip system, the drip spikes can easily be inserted directly into the rockwool cubes.

Depending on the manufacturer of your rockwool cubes, there may be plastic wrapped around the cubes. Some growers remove this, while others simply poke some holes on the sides and bottom to allow water to drain off. We recommend the second option because the plastic will help to reduce the amount of algae from growing on the top of the moist cubes and will work just as well for the plant.

3. Maintain the system

Maintaining rockwool is simple, just ensure it does not dry out or stay submerged in water. That's it! 

If you have chosen to use smaller rockwool cubes, your plants may outgrow them. This can be seen when the outsides of the cubes are completely covered in roots. At this point, simply place this smaller rockwool cube directly into a larger cube or slab, or into another substrate such as clay pebbles or grow stones.

Choosing an irrigation method for rockwool

As we have discussed, rockwool is a perfect medium for hydroponics and can be used in many different ways.

1. Drip systems 

The most common method by far is to connect each cube or slab to a drip spike. This allows the cubes to remain moist without being submerged in water for too long. Drip spikes are incredibly easy to use, and can be inserted into any size of rockwool cube. We recommend this for anybody just starting out with hydroponics, or who simply want an easy and effective way of growing nearly any plant with hydroponics.

To move the plants, simply unhook the spike and move the plant to another location. Most large scale growers choose to grow using this method with rockwool.

2. EBB and flood 

EBB and flood is another great method for growing with rockwool. You can place the cubes directly into your flood table, or bury them in a pot with clay pebbles or grow stones. Ensure that the flood phase is high enough to completely soak the roots and rockwool, without drowning the entire plant. And also ensure that the drain phase is long enough to allow the rockwool to dry out just slightly. This balance is not hard to achieve, but will require some tweaking of the pumps and timers.

Rockwool has nearly become a staple in the world of hydroponic growing, and for good reason. While it is perfect for beginners and experts alike, it can be used in all stages of plant development, and either alone, or in combination with other mediums. Rockwool growing is modular, cost effective, and cheap to transport and store.

Pick some up today and find out first hand why so many hydroponic growers choose rockwool as their substrate of choice!