Growing Hemp with Stonewool

Posted on August 17, 2020 by Red Rock Block

Stonewool and Hemp: A Dynamic Duo

stonewool-veg-cubesStonewool has a past that is very diverse with its origins in the construction industry as an insulation for buildings. This material is still used today as an insulation material. In the late 1960’s Denmark scientists conducted tests on various materials to see their effectiveness as a soilless growing media. Stonewool proved to be an excellent alternative and the hydroponics industry has never looked back!

This material is the result of basaltic rock melted and spun into thin fibers that is pressed into various sizes and shapes. Regardless of the strain and variety of hemp, stonewool is an excellent growing media for all stages of life. Studies and data have shown that stonewool in commercial applications have generated larger yields and higher quality in comparison to other growing mediums.

What is stonewool and is it safe? 

flowering-stonewool-grow-mediaStonewool is also referred to as mineral wool and is one of the most widely used and popular media in the commercial hydroponic industry.  Not only can this material be used in the commercial industry, it is also a great media for the small scale grower. This material wasn’t always used for growing plants. In fact, this material has origins in the construction industry with insulation applications. When the basaltic rock was melted and spun into thin fibers and wrapped into sheets, builders found that the insulating properties of the material were excellent for all buildings. Then in the 1960’s Denmark researchers conducted studies on the ability of stone wool to support crop growth. After these studies, stone wool was further developed and engineered to support plant growth even better! Now it is one of the top media to grow plants no matter the scale.

The process is relatively simple. The material is produced by melting basaltic rock and spinning the molten material into the thin fibers which are cooled by a stream of air. These fibers are molded into many different shapes that growers can use in their operations from stonewool starter plugs, cubes, slabs, and blocks. Although this is a man-made substrate, the material is often regarded as a natural product as it is derived originally from rock. The material is safe for most types of plants throughout all stages of the growing process. However, when handling the product before wetting it down, workers are advised to wear PPE to protect from dust and other particles produced in handling. After the material is set in place and integrated fully into a system, it is perfectly safe not only for plants, but for workers as well.

Stonewool and Hydroponic Use

stonewool grow block videoThere are a few points that need to be considered and met when using stonewool as a growing medium. As the original material used in the making of stonewool is naturally alkaline, the pH will need to be adjusted according to plant needs. For hemp this can easily be done by pre-soaking the cubes in water for 24 hours. The water should balance the pH at around 5.8-6.3. Using the material and transplanting to larger sizes is a relatively easy task, as the material can be cut and shaped accordingly.

Once the plant reaches the correct size, the stonewool starter cube or block it can be placed in a cut hole in a large slab or block. Small anchors will need to be placed until the roots grow into the new material. Then the anchors can safely be removed. Stonewool in a hydroponic system has many benefits that make it the better alternative to traditional methods of cultivation. Oftentimes with other grow media such as coco coir, the system can become clogged and backed up preventing the flow of water to crucial areas of the system. Stonewool on the other hand, is tightly woven and does not degrade in a system.

Stonewool Containers and The Right Choice for the Stage of Growth

stonewool-container-grow-opAn additional benefit of stonewool is the readiness of seedlings to root to the material. Smaller cubes and plugs are ideal for starting from cuttings and seeds. Once the roots begin to sprout through the bottom of the plug, the plants are ready for transplanting to larger cubes or blocks. Transplanting with stone wool is very simple and easy. A grower can either transplant into pre cut holes in the slabs or blocks or cut a custom sized hole for the plants. By placing the smaller block into the space and pinning until roots grab a hold of the new space is all a grower needs to transplant.

This method is ideal to preserve roots and ensure minimal root breakage. It is because of this that the plants are not stressed and do not slow in their growth. The ability to place these plugs or smaller cubes into the larger material is also ideal from a space and organization standpoint. If there comes a time that the material becomes root bound, the grower can always transplant into a larger block or slab with the same method  with plugs. Stonewool can be used in all varieties of hydroponic systems such as NFT, DWC, flood, top fed, and even hand watered systems.

Interested in more information about RedRock Block’s high quality, commercial-grade stonewool grow media? Call- 1-310-967-2025 or visit-

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