Grodan Guide to Stone Wool Growing Media for Indoor Plant Cultivation - Indoor Farmer

Stone wool, also known as wool or mineral wool, is a type of soilless, inert growing media ideally suited to indoor cultivation of all plants, from plant to vegetables and floriculture.

Grodan invented and debuted stone wool in 1969, and in the decades since then, our company has led the way in advancing indoor gardening technology. We love to share our knowledge on best practices for rapid root development, and how to achieve consistent, efficient production and maximum yields with minimal resource inputs.

There’s a reason stone wool is the preferred choice as a substrate, thanks to its compatibility with both soil-based and hydroponic cultivation systems for irrigation, lighting, automated nutrient delivery and other top precision growing techniques.

The standardized size and shape of each Grodan stone wool product make it easy for cultivators to build a graduated system that grows with seedlings through maturity and harvest. And after the growing cycle is complete, stone wool is recyclable in more and more places around the world.

What Size Stone Wool Plugs, Cubes, Blocks and Slabs Should I Use?

There are a variety of stone wool products that can be used individually or as part of a complete indoor cultivation system that optimizes efficient growth with minimal inputs throughout the plant life cycle. There are options for hydroponic systems as well as growing in containers.

Grodan Starter Plugs™ are designed for starting seedlings and rooting stem cuttings. The Plugs fit into Gro-Blocks, Gro-Cubes and the Grodan Gro-Slab once plants are ready for a larger-sized growing medium.

Stone wool Gro-Blocks are the next-largest product size to starter plugs and can be combined with the stone wool Grow-Cubes as well as Gro-Slabs across different phases of growth or for various irrigation methodologies.

Grodan Hugo™ Gro-blocks are designed for transplanting cuttings into a final block configuration that will carry plant growth through harvest. They have special channels at the base to promote full drainage and uniform planting holes that seat individual plants at the optimal depth to encourage swift root development.

Starting Seeds in Stone Wool

One reason that Grodan stone wool products have been so popular with cultivators since 1969 is the efficiency and ease of use of this growing medium for hydroponic systems , from germination through harvest. Stone wool streamlines seed starting, cutting propagation and maintenance of mother plants to ensure a consistent production schedule.

Popping seeds is as simple as prepping the stone wool substrate of choice to the preferred pH level, inserting the seeds, irrigating and waiting for shoots and roots to emerge.

The stone wool substrate supports the rapid establishment of small seedlings and cuttings by ensuring adequate uptake of nutrients and water during the crucial early rooting stages. 

Rooting Clones in Stone Wool

For cultivators conducting clonal propagation, planting and rooting with stone wool further enhances the consistency of growth characteristics from the mother plant to the final harvest.

The standard size and shape of Grodan’s Starter Plugs and Grow-Cubes help cultivators achieve uniform growth across a batch of clones and ensure rapid, healthy root development.

Vegetative Development With Stone Wool

When seedlings or clones have rooted through, they are ready for transplanting into Gro-Blocks, a Gro-Slab or Grodan Loose Media designed for containers. This crucial stage in efficient plant cultivation  is when root zone management can be used pre-emptively to avoid plant shock and stunted growth from overwatering, underlighting or inconsistent temperature within the substrate.

How cultivators approach root zone management  depends very much on the type of growing media they’re utilizing.

Root zone management is achieved by using precise measurements of each plant’s individual climate conditions and a clear understanding of how the substrate behaves to achieve tightly choreographed vegetative growth.

Stone wool is designed to retain moisture and nutrients through drip irrigation cycles as well as flush out easily for cultivators using the drying back method or making pH adjustments.

Precision Growing and Irrigation With Stone Wool

Stone wool also offers singular benefits compared to other substrates for the important transition to flower development after plants have bulked up and established a healthy root zone in the vegetative phase.

Finding the desired balance between vegetative and generative growth requires a smart plant irrigation strategy  tailored to the plant cultivar’s unique genetics and growth habits, the cultivator’s goals for the end product, and how the root zone was established and managed during previous growth stages.

Gro-Blocks and Hugo Block products make it simple to calculate irrigation needs due to their uniform size and dry weight. Monitoring and measuring the weight of a stone wool Gro-Block regularly throughout the irrigation process is one way cultivators can determine the timing and allotment of daily water to introduce. It also makes it easier to get a sense of the stone wool substrate’s water retention and drainage cadence.

For example, for Hugo Blocks, Grodan recommends smaller water volumes introduced on a more frequent cadence during the vegetative growth phase, while the reverse is true during the generative phase. Weighing Gro-Blocks also helps to determine runoff, and re-saturation rates can be dialed into the production balance that the cultivator wishes to achieve through hydroponic systems. Weight monitoring can also assist with troubleshooting as cultivators finesse their drip or flood allotment.

This article was used with permission by Grodan and edited for length and relevance to our customers. For the complete guide in more detail, and other articles by Grodan, please visit their blog