In our 100s series of How-to-Grow Cannabis, we focused on growing in soil and basically didn’t touch any other growing media. We focused on soil because it’s perhaps the easiest to use. Good soil is alive and will generally maintain itself. It only needs inputs occasionally. However, soil is also very constraining — it tends to take the most space and your plants may not grow at their most efficient in it.
So today we’re going to cover some of the most common media types you will generally find in a commercial or caregiver setting, the pros and cons of each, and why you might prefer one medium over the other. No media is able to do everything perfectly, so pick the one most appropriate for your style of growing.
- Without a doubt, rockwool is the cleanest media on the market. Very little microscopic life can survive on it without your assistance, and it’s dangerous for insects because the microscopic rock can slice up their exoskeletons.
- Rockwool is reusable with a little bit of work, sometimes referred to as “recharging.”
- Rockwool can be reshaped or cut into smaller sizes, just make sure to wear a respirator if you choose to do so.
- Rockwool retains whatever shape it is given, making it ideal for transplanting.
- Rockwool drains really well and provides excellent oxygenation for plant roots. If you’re running a hydroponic setup, rockwool can make your life easier.
- Rockwool requires preparation to be used, sometimes called “charging.” Generally the rockwool when it’s first received is at a pH that is not conducive to plant life, and it will need to be placed into a water solution with a pH of about 4.5-5 pH to get it to the proper acidity.
- Rockwool is formed from microscopic fibers of rock. Like any other rock fiber, it is dangerous to inhale small fragments. If you wash it before use, you should generally avoid the worst of this problem.
- Rockwool is probably the most finicky of mediums, and will require more active maintenance than other mediums.
- Rockwool is not recyclable. Luckily, you shouldn’t feel too guilty about throwing it out if you need to, because it’s literally just rocks.
- Rockwool is one of the most expensive mediums on the market. For this reason, many growers opt to use rockwool only during the propagation stage to reduce their costs.
- Coco is environmentally friendly. Since it is made from coconut husks, it can be disposed of in compost.
- Coco is easy to use, like soil, and can even be mixed with soil for a mix-and-match style of growing.
- Coco is generally ready to go out of the bag, and will pour to meet its container’s size.
- Not all Coco is made equal. Mixes of coco that are not made for professionals (Pro Mixes) may carry insects or microscopics that can cause issues. Don’t try to save an extra dime if it costs you your whole crop.
- Coco has limited reusability. Because it is organic, it will tend to carry over nutrients, bacteria, and insects from the previous grow. Most professional growers will opt for a new batch of coco with every cycle, and the cost can add up with this. Some growers will reuse their coco and “flush” it, but over time the coco will become unusable.
Peat, short for peat moss, is an amendment made from sphagnum moss. While peat is generally not sold in its own right as a medium, it is commonly used as a blend or amendment in a large variety of other media.
- Peat is organic, as it is made from moss. Can be composted or disposed of with minimal concern.
- Peat retains water like a sponge, and can help moderate periods of drought or dryness in either a hydroponic or traditional grow.
- Generally easy to work with, and mixes well with most mediums.
- Because it is organic, it may need to be disposed of periodically. Reuse can gradually diminish its usefulness and even begin to host harmful microbes or insects.
- While peat is great for water retention, this can become a serious problem if you overwater your plants. The peat will hold onto water for a very long time which can lead to other issues associated with overwatering.
Essentially small rocks, perlite, clay, sand, and pebbles can all serve as a simple, cheap, and reusable media. The early days of hydroponics most frequently made use of these materials, and they are considered “classic” in the hydroponics worlds.
- Reusable and cheap.
- Generally clean, and comes in a wide variety of different sizes and shapes.
- Only minimal work is required to prepare these materials.
- Transplanting from these materials into a different media is not advisable. Due to their less-than-solid nature, a plant’s roots could be irreparably damaged if this media is disturbed too much.
- Similarly, it’s recommended that these media are kept in a solid container made of hard plastic, metal, or ceramic. Cloth containers, soft plastic, or other soft containers could move the material and damage the plant’s roots.
- Disposal of these materials may be tricky depending on how much of it you need to dispose of.
It’s worth mentioning our good old friend soil too. Not much else needs to be said, so here are the pros and cons.
- Probably the cheapest and easiest medium to obtain. You can buy some virtually everywhere.
- Easy to use.
- Easy to dispose of or reuse.
- Comes with its own nutrients.
- Has the highest chance for pathogens or insects to be carried with it.
- Takes up more space than most of the other mediums, and requires amending (or special potting soils) if you are growing indoors.
- You have very little control over soil, other than adding things to it.
Mixing and Matching
Most growers we’ve spoken with often mix and match their mediums based on their needs. I alluded to this above when I was talking about cost and reusability:
- Rockwool is great for transplanting from, as it retains its shape really well and keeps roots disease-free. However, it is the most expensive medium, so many growers choose to use it at the propagation stage only.
- Coco and peat are great for stages when the plant is growing larger and you need more volume in your media. They’re relatively cheap and relatively clean, and best suited for early vegetative state all the way through flowering.
- Perlite, clay, sand, and pebbles would be best-suited towards the middle or end of a plant’s lifespan, as transplanting from them is impractical, but they have many of the benefits of rockwool.
- Soil is useful for the entirety of a plant’s lifespan, but carries a greater risk of disease and is harder to control.
That covers the bulk of media (pun intended) used in the cannabis industry. Is there a niche material you like to use? Let us know on the forum or in the survey below!
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About the Author
Hunter Wilson is a community builder with Growers Network. He graduated from the University of Arizona in 2011 with a Masters in Teaching and in 2007 with a Bachelors in Biology.