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  • Writer's pictureAlexis Mellons

Peat moss or Rockwool for clones: What substrate is best for your cannabis grow?

When given the option between Rockwool and peat moss for your grow's next clone purchase, how are you supposed to choose? Though each grow tends to have their preference—whether by how they were taught, what the costs are, or what’s available from their source—there’s a lot to consider when choosing a cloning medium. Water retention, aeration, and environmental impact… the nuanced differences between substrates can get confusing! Below, we’ll break down the key differences between Rockwool and peat moss, so you can make a more informed decision for your next round of cannabis clones.

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What is Rockwool?

Rockwool is a sturdy and reliable substrate for cannabis cloning. Yellow-ish in color, and packaged in perforated slabs for bulk propagation, you’ve likely seen this material before. Made from molten basaltic rock, which is spun into thin fibers, Rockwool has a history of popularity in the cannabis industry. Originally used for construction insulation, growers started using Rockwool in the 1960’s, taking advantage of its lightweight and sponge-like characteristics. Rockwool is celebrated for its ability to retain water, nutrients, and air; however, it comes with some environmental setbacks and a higher price tag, which your cannabis grow may want to avoid.

Rockwool has a great reputation for not only providing thorough drainage, but also necessary water retention. The key to Rockwool’s success is the material’s “moisture gradient.” While excess water will sit at the lower layers of the Rockwool, the top layers of the substrate will begin to evaporate. As the block dries out up top, fresh air seeps into the upper layer, allowing fresh oxygen to reach the roots. The composition of this material also allows your clones to draw water from Rockwool at low moisture tensions (facilitating hydration at low levels of water). Because water retention is so high with Rockwool, it’s best to water your clones in shorter, smaller bursts, so as to not drown your cannabis plants. Because the top layer is meant to dry out, over watering can occur if you’re only looking at the surface.

Rockwool’s structure aids not only in water retention, but also in ideal root aeration. Its airy yet secure composition doesn’t fold under the weight of water and nutrients, helping to prevent root rot.

Another reason to buy your cannabis clones in Rockwool is its sterility, a great factor for growers who want high precision in their custom nutrient regimens. While this means you have full control over the plant’s diet—as they’re subjected to no additional nutrients, seeds, pests and pathogens—it also doesn’t offer any microbiology some cannabis growers find essential to the growth process. This also means you’ll need to provide additional nutrients to your clones, compared to other substrates, which may scare off grows on a tight budget.

The biggest disadvantage to using Rockwool as a substrate for cannabis cloning is its notorious reputation for being environmentally UNfriendly. Being basaltic rock, it is indeed 100% organic; however, it does not break down or decompose over time for the same reason. If your grow has taken a stance on going green, this may not be the choice for you.

Cannabis clones in peat moss
Our growers typically use peat moss for clones, but we're equipped to prepare your clones in Rockwool, too!

What is Peat Moss?

Peat moss is a natural substrate made from a variety of decomposed mosses. Growers know it to be useful for producing richer harvests and improving the root structure of cannabis plants, and it has great acidifying qualities as well. Overall, peat moss does more on its own to care for the cannabis plant than most other substrates, but it does come with its own set of challenges, which we’ll discuss below.

The most popular reason to reach for peat moss is its biology. This natural material is full of microorganisms most growers find helpful to the growth process, as it provides a more nourishing environment than a substrate such as Rockwool. This also means you don’t have to provide as many additional nutrients and fertilizers, comparatively, which equates to a better bottom line. Add to this, peat moss has a slightly higher pH (which helps to properly acidify the plants), and it comprises elements like sulfur, which benefits terpene development and leads to better tasting buds.

Peat moss is also well-known for its ability to hold water, which it does twentyfold (yes, that’s 20x its weight). This allows your clones to stay well-hydrated for a long time, an important factor for getting nutrients to the plant. However, the structure of peat moss isn’t the strongest of the substrates, and its shape can cave in on itself if the water weight becomes too overwhelming. This can affect how much oxygen reaches the cannabis roots, so monitor with care.

A living organism, peat moss is 100% biodegradable. In fact, the plug is transplanted with the clone, where it breaks down and adds back to the soil. However, like Rockwool, peat moss does pose its own unique environmental challenge. As more moss is mined from peat bogs, the industry adds more damage to ecosystems, endangering native flora and fauna. The issue of sustainability is an important one for the peat moss industry, and could affect the cannabis industry as a result.

Peat Moss vs. Rockwool: A Simple Comparison

Now that we’ve gone in depth about the key differences between peat moss, let’s quickly recap:

Water Retention

For maintaining a fully saturated environment, peat moss has the advantage of holding an immense amount of water throughout the clone plug. For superior aeration and root penetration, Rockwool is the better choice.


Rockwool is a completely sterile environment, with no nutrients contained or added. If you want full control over your nutrient and fertilizer regimen, Rockwool is the best choice for your cannabis clones. Peat moss offers a natural environment, complete with beneficial organisms, minerals, and acidity. Both substrates can be used with added nutrients and fertilizer.

Environmental Impact

Though Rockwool can be reused, it cannot break down, causing a hasher impact on the Earth than peat moss. Peat moss is 100% biodegradable and is an excellent choice for grows who have committed to Going Green.


Whether transplanting clones in Rockwool or in peat moss, the method is the same. Simply place the clone, with substrate still attached, into your soil. There is one difference to remember, however. Unlike Rockwool, the nutritious peat moss will break down and feed the new environment over time. Though the Rockwool won’t take from the new environment, it doesn’t add anything either.

By default, our team uses peat moss plugs for our cannabis clones. However, the growers at Summit Genetics are equipped to prepare your clones in either medium, Rockwool or peat moss. In submitting your order, let our sales team know which you prefer, and we’ll have it ready for you (please allow 7-10 business days for Rockwool clones to be ready). If you’re unsure which substrate is best for your cannabis grow, you can always contact our sales team for some direction! We’re always thrilled to help you navigate the fun yet precise art of growing cannabis.






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