Rockwool vs Rapid Rooter vs Coco: Choosing a Cloning Medium

Two of our regulars got into a friendly standoff at the counter a while back. One is a hydro grower who will not touch anything but rockwool, swears it is the only consistent way to root a cutting, and buys cubes by the case. The other roots everything in Rapid Rooter plugs, thinks rockwool is a fussy, itchy hassle, and has the rooted clones to prove her point. Here is the thing: they both run success rates north of ninety percent. They were arguing about a preference and calling it a fact.

That is the honest starting point for this whole comparison. There is no single best cloning medium. Rockwool, composted starter plugs like Rapid Rooter and Root Riot, and coco each win for a different grower, a different setup, and a different tolerance for fuss. The right pick depends on what you grow in, how many clones you take, and how much babysitting you want to do, not on which one is objectively superior. We stock all of them, we will set you up with any of them, and we are going to tell you what each one is actually good and bad at so you can choose. We don't upsell. If you want the full cutting-to-roots process first, start with our step-by-step guide to cloning cannabis; this article is just about the medium you stick the cutting into.

First, what a cloning medium actually has to do

Before pitting the three against each other, it helps to know the job they are being judged on, because once you understand that, the tradeoffs make sense instead of feeling arbitrary. A rooting medium has three jobs, and only three.

The first is to supply moisture and oxygen at the same time. This is the one most people miss. A cutting's future roots need water, obviously, but they also need air, and a medium that is waterlogged has driven the oxygen out. UNH Extension's propagation primer puts it directly: the rooting medium must support the cutting and also supply both moisture and oxygen to the developing roots. The best media hit a balance, holding enough water to keep the cutting hydrated while keeping enough air for roots to breathe. The second job is to physically hold the cutting upright and in contact with that moisture. The third is to stay clean, because a cutting is an open wound and a dirty or reused medium is a common way to introduce the rot that kills clones.

Two facts fall out of those jobs and apply to every medium below. One, soggy is the enemy. According to Michigan State University Extension, too much moisture during propagation leads to waterlogged substrate and the loss of cuttings to rot or botrytis, so the goal is enough moisture to prevent wilting, not a drenched cube. Two, the medium is rarely the bottleneck. As Greenhouse Product News propagation guidance notes, most cuttings root within about two to three weeks when the environment is right, regardless of the specific substrate. Keep both in mind as we go.

One more distinction explains a lot of what follows: some media are inert and some are organic. Rockwool is inert, meaning it holds no nutrients of its own and starts at a high pH until you condition it, so you feed and control everything yourself. Composted plugs and coco are organic or semi-organic, sit closer to a usable pH, and carry a little buffering capacity, which makes them more forgiving but slightly less precisely controllable. Neither is better in the abstract. Hydroponic growers tend to want the blank, controllable slate of an inert cube, while soil and coco growers tend to prefer the forgiving feel of a plug or coco. Knowing which camp you are in answers most of the question before you read another word.

Rockwool (mineral wool) cubes

Rockwool, also sold under the Grodan name and often called stonewool or mineral wool, is spun from molten rock into a fibrous cube. It has been the commercial propagation standard for decades, and for good reason: when you use it correctly, it provides an almost ideal balance of water and air, and it does so consistently, cube after cube, with no organic material to break down or vary.

What rockwool is genuinely good at is consistency and integration with hydroponics. Because it is inert and sterile out of the wrapper, it does not introduce pests or pathogens and does not feed or buffer the cutting, which means you control the inputs precisely. A rooted rockwool cube drops straight into a larger rockwool block, a net pot, or most hydroponic systems with zero transplant shock, which is exactly why hydro and rockwool growers reach for it. Bought in bulk sheets, it is also one of the cheapest options per cutting, so it scales beautifully for anyone running trays at a time. Many growers also like that rockwool makes rooting easy to monitor, since white roots emerge visibly from the sides and bottom of the cube when a clone is ready to move.

The honest downsides are real and worth knowing before you commit. Rockwool is naturally high in pH, so it must be conditioned before use: you soak the cubes in pH-adjusted water, usually around 5.5, before sticking your cuttings, and skipping this step is a classic reason rockwool clones stall. It also holds a lot of water and drains slowly, which is a gift if you are disciplined and a curse if you tend to overwater, because a saturated cube is exactly the rot risk the propagation research warns about. It is not biodegradable, which matters to some growers on disposal grounds, and the fibers can irritate skin and lungs, so most people wear gloves and avoid breathing the dust. None of this is a dealbreaker, but it is more process than a plug.

Buy rockwool if

You grow hydroponically or in rockwool, you clone in volume and want the lowest cost per cutting, and you are comfortable pH-conditioning your cubes and managing moisture carefully. It pairs naturally with the systems in our hydroponic cannabis guide and DWC guide.

Skip rockwool if

You grow in soil or coco, you only take a handful of cuttings, or you would rather not deal with soaking and pH-conditioning. A plug will be easier and transplant just as cleanly into your medium.

Composted starter plugs: Rapid Rooter and Root Riot

Starter plugs are the small, spongy cylinders made from composted organic material, usually a blend of peat or composted bark bound together, with a pre-formed hole in the top for your cutting. The two names you will see most are Rapid Rooter, made by General Hydroponics, and Root Riot. They are close cousins: both are composted plugs that do the same job in the same way, and for cloning purposes the differences between them are minor. We will come back to that, since plenty of growers specifically search Rapid Rooter versus Root Riot.

What makes plugs the easiest option, and the one we hand most beginners, is that they are forgiving and ready to go. There is no pH-conditioning ritual: you lightly moisten the plug and stick your cutting. They hold water and air in a comfortable middle ground that is harder to get badly wrong than rockwool, and because they are made of organic material that roots love to grow into, they transplant beautifully into soil or coco, plug and all, with no disturbance to the new roots. They are biodegradable, they are clean, and they just work.

The tradeoffs are modest. Plugs cost more per cutting than a bulk sheet of rockwool, which adds up if you clone hundreds at a time, though for a home grower taking a dozen cuttings it is pocket change. Because they are organic and relatively small, they can dry out faster than a dense rockwool cube if you forget about them, so they reward a closed dome and a glance every day or two. And there is some batch-to-batch variation in any organic product, so an occasional plug is denser or looser than its neighbors. Using them is simple: moisten, insert the cutting up to its lowest remaining leaves, optionally dip the stem in rooting hormone first (an auxin like IBA, which MSU Extension notes speeds and evens out rooting), dome the tray, and wait. A common rookie error with plugs is leaving them sitting in standing water; they root best simply damp, with any excess drained off, not waterlogged in the bottom of a tray.

Rapid Rooter vs Root Riot, briefly

People want a winner here, and the honest answer is that it is close enough not to lose sleep over. Both are composted starter plugs that root cannabis well. Growers report minor differences in texture, sponginess, and how wet each likes to be, and availability or price at your shop often decides it more than performance. If you have a setup that works with one, there is no compelling reason to switch to the other. Buy whichever your store stocks at a fair price.

Buy starter plugs if

You are newer to cloning, you grow in soil or coco, or you simply want the most forgiving, lowest-effort medium that transplants without drama. This is the default we would hand most home growers.

Skip starter plugs if

You clone at large volume and want the absolute lowest cost per cutting, or you run a pure hydroponic system where a sterile, inert cube integrates more cleanly. Rockwool will serve you better there.

Coco coir

You can also root clones directly in coco coir, the same processed coconut husk fiber many growers use as their main medium. It is cheap, it is renewable, and it has a naturally good structure for young roots, holding water while still draining and breathing well. For anyone who already grows in coco, it is arguably the most logical choice, because the clone never has to change substrates: it roots in coco and grows up in coco.

The appeal of coco for cloning is that seamless pipeline plus its forgiving, airy texture. A small amount of moist coco in a cup or a cell tray supports a cutting nicely, drains off excess water so the stem is less likely to drown, and lets roots breathe. When the clone is ready, you simply pot it up into more coco with no transplant shock at all. It is also the friendliest option for growers who dislike both the fuss of rockwool and the per-plug cost of starter plugs. It also rinses off hands and tools easily, which is part of why coco growers tend to find the mess more annoying than actually problematic.

The downsides are mostly practical. Loose coco is messier to work with than a tidy cube or plug, and it does not hold a cutting as rigidly, so you need a small container rather than a bare tray. You also take on moisture management yourself, keeping the coco damp but never soggy, and quality coco should be properly buffered and pH-appropriate, since raw, unbuffered coco can lock up nutrients and sit at an awkward pH. None of this is hard, but it is more hands-on than dropping a cutting into a plug. Once your clones have rooted and you move them on, our coco watering and feeding guide covers keeping them happy, and if you are still deciding on a base medium, soil vs coco vs hydro compares the bigger picture.

Buy coco if

You already grow in coco and want a seamless, low-cost pipeline from cutting to plant, and you do not mind a little mess and managing moisture yourself.

Skip coco if

You want the tidiest, most plug-and-play experience (use a starter plug) or you run hydroponics (use rockwool). Coco shines specifically when it matches your final medium.

The honorable mentions: water, aero cloners, and plain soil

Three other approaches deserve a mention, even though they sit a little outside a straight rockwool-plug-coco comparison. The first is plain water: stick the cutting in a few inches of clean water, and roots will often form. It costs nothing and is a fine way to learn, though water roots can be slightly more fragile at transplant and still water can stall. The second is an aeroponic or bubble cloner, which roots a bare stem with no medium at all by misting it or suspending it over oxygenated water; these root fast at volume but cost more and demand cleanliness. The third is rooting directly in a light, airy seed-starting soil mix, which works much like coco for soil growers. We compare the full set of methods, medium and machine alike, in the main cloning guide, so this article can stay focused on the three solid media most growers actually choose between.

Peat pellets, Oasis cubes, and a few other options

The big three cover most growers, but you will run into a handful of other media, and it helps to know where they land. Jiffy-style peat pellets, the compressed discs that swell when wet, behave like a softer, looser starter plug and can root cuttings fine, though some growers find they hold a touch too much water and vary from disc to disc. Oasis cubes and similar floral-foam products are synthetic foam blocks with a clean, uniform structure that some propagators prize for consistency, sitting somewhere between rockwool and a plug in feel, though they are less common on hobby shelves. Loose perlite, or a perlite and vermiculite mix in a cup, roots cuttings cheaply and with excellent aeration, at the cost of being messy and not transplant-friendly as a single unit. And a light, sterile seed-starting soil mix behaves much like coco for soil growers. None of these beat the big three for most people, but if your shop stocks them or you already have them on hand, every one of them will root a healthy cutting in the right environment. If we had to grab one off this list for a beginner, it would be the peat pellet, for the same plug-and-play reason we recommend Rapid Rooter and Root Riot.

How to choose: match the medium to your grow

Strip away the brand loyalty and the choice comes down to four honest questions about your own setup.

Notice that the deciding factor is almost always your final medium and your scale, not some inherent superiority. Pick the medium that matches where the clone is headed, and you remove a transplant step and a chance to stress the plant. That is the whole game.

Transplanting out of each medium, and timing it right

The medium you choose also shapes how you move a rooted clone into its next home. The universal rule holds across all of them: transplant once you see a few healthy white roots, not before, and handle those new roots gently because they are fragile. Where the media differ is in how cleanly they hand off. A rockwool cube or a starter plug is the easy case, since you simply set the whole cube or plug into your next container or block and the roots grow out into the new medium with essentially no disturbance and no shock. Coco is nearly as clean when your next medium is also coco, because you pot the rooted plug of coco up into more coco. Water-rooted and aero-cloner clones take the most care, since their bare roots are meeting a medium for the first time, so keep humidity up and light gentle for a day or two while they settle. Whatever the medium, do not let a rooted clone sit too long in a tiny cube starving for space; pot it up promptly once roots show and it will reward you with fast early vegetative growth.

Does your medium change how you feed and water clones?

A little, and it is the last piece worth understanding. While a cutting is actually rooting, it barely feeds at all, so for the first week or so the medium changes almost nothing: plain pH-appropriate water or a very dilute solution is all any of them want, because a rootless cutting cannot take up much. Once roots appear, the inert-versus-organic difference shows up. A rooted clone in rockwool or coco will want a light nutrient feed fairly promptly, since those media hold little to nothing for the plant on their own. A clone in a composted plug or a soil mix has a small amount of buffering and gentle nutrition to lean on, so it can coast a bit longer before it needs feeding. None of this is dramatic at the clone stage, but it is why coco and rockwool growers tend to reach for nutrients sooner than soil growers do, and it is worth knowing before you move rooted clones into veg.

The mistakes that matter more than your medium choice

Here is the part that keeps this from being a sales pitch for any one product. Whichever medium you choose, the same handful of mistakes will tank your clones, and they all outrank the medium debate. Overwatering is the big one: any medium kept soggy will rot a cutting, and as the propagation guidance makes clear, waterlogged conditions invite rot and botrytis. Dirty tools, reused plugs, or an uncleaned cloner introduce disease no matter how good the substrate. Skipping the pH-conditioning step on rockwool sets those cubes up to fail. And a cold root zone stalls rooting in rockwool, plugs, and coco alike. We see this constantly at the counter: a failed batch almost always traces back to one of those four, and the brand of cube in the tray turns out to be a footnote by comparison.

In other words, a grower who runs cheap coco in a clean, warm, properly humid setup will beat a grower who runs premium rockwool in a cold, soggy, dirty one every single time. If your clones are struggling, the medium is rarely the culprit; our guide to why clones fail to root walks through the real causes and fixes, and the VPD chart for cannabis helps you keep humidity and temperature dialed. For where all of this sits in a full grow, the week-by-week cannabis grow guide is the map. We stock rockwool, Rapid Rooter, Root Riot, and coco, and we will point you to whichever one fits your grow, not whichever one has the best margin. We don't upsell.

Frequently asked questions

When you are ready to choose, the cloning media and propagation supplies in this comparison (rockwool cubes, Rapid Rooter and Root Riot plugs, coco, humidity domes, and rooting gels) all live in the Modern Farms catalog under Plant Care and Environmental Control, and our team is happy to match you to the one that fits your grow. Because, as always, we don't upsell.

For informational and educational purposes only. This article is general horticultural guidance and is not legal advice. Cannabis cultivation laws vary by country, state and locality, and growing cannabis may be illegal where you live. Always understand and comply with the laws and regulations that apply to you before propagating or growing any cannabis plant.