Very similar to peat moss, sphagnum is a moss composed of dehydrated acid-bog plants. Being perhaps the most desired moss for agricultural use, it is expensive to produce and as such, it is often used in soilless mixtures alongside peat moss. Sphagnum has very high water-absorbing properties and can absorb 10 to 20 times its dry weight in moisture. Sphagnum moss has a pH between 3.5 and 4.0. Much like peat, sphagnum offers excellent buffering qualities for the root structure, helping to prevent nutrient burn and making it very forgiving for beginner growers.
Chemically speaking, vermiculite is hydrated magnesium-aluminum-iron silicate. It expands quite a bit when heated, and once expanded, it is extremely lightweight. It is insoluble in water, inert and can absorb huge amounts of water, which is why it is often a key ingredient in soilless mixes. Furthermore, its high cation exchange capacity makes it very good for buffering and use with heavy nutrient programs.
Similar to vermiculite and perlite, clay can be heated and expanded. However, with clay, the medium becomes much harder after heating. Still, the clay aggregate is porous enough to give it some decent water-holding ability, though not enough for systems using a single daily watering. Rather, this medium is better suited for continuous-flow or multiple-watering hydroponic systems. Inert and sterile with neutral pH, HEC offers little to no buffering properties, but it is highly stable and capable of holding seedling or clone plugs in active hydro systems. HEC can also be used as a bottom layer for drainage in plant containers or as a mixed-in additive for soilless mixtures.
Long-time reader, first-time grower here! As my wife and I begin our journey in growing, I wanted to get your take on the abundance of indoor grow mediums currently available on the market. As first time growers, we are leaning towards using soil and hand-watering the plants, as I have seen you recommend this approach for beginners several times over the years. However, we are open to doing a hydro system if the medium and system are easy enough to handle. Any advice is much appreciated!
Hardened expanded clay (HEC) being used in a flood-and-drain hydro table.
About Less Common Types of Hydro: Some people grow with plant roots suspended in misted air (aeroponics), in an assembly line (NFT), or in a tank with fish (aquaponics), but these are better suited to smaller plants, and not commonly used to grow cannabis.
So what’s REALLY the best medium? Alright, I’ll stop dancing around what you’re really here for. I’ll rank the popular mediums for different aspects, then I’ll tell you which one I think is the best overall…
When growing in a soilless medium, you can treat your plants almost the same as if growing in soil. The main difference is you feed all their nutrients in the water. As a result of your plants getting nutrients delivered directly to their roots, you will often get quicker growth and higher yields than growing in soil (where the roots have to seek out nutrition).
Best of the Best: Grow Medium Roundup
By the end of a hydro grow, you may find yourself with huge masses of roots!
Note: The contenders are Soil, Living Soil (composted), Coco Coir (soilless), Hydro (DWC – roots suspended in water)
Hydroponics can be really scary, but I’ve seen so many first-time growers get great results with hydroponics. The most important thing to remember is to follow the instructions and always get a root supplement like Hydroguard. I love hydro. After growing for several years, I think it may be my favorite grow style. You get the fastest growth and most control over nutrients of any grow medium!
Conclusion: What’s the Best Grow Medium for Growing Cannabis?
Least Chance of Bugs/Pests:
When growing cannabis in containers, for example with soil or coco, it’s important to give your plant roots enough room to grow. If they run out of space, it will limit the size of your plant, and often causes nutrient deficiencies and other problems like persistent droopiness. If your roots have circled around the edges of the container, it is rootbound and should be transplanted to a bigger container immediately!
While ‘clean’ Coco tends to keep pests at bay, the challenge is finding it. Most Coco Coir comes from Sri Lanka, India, Brazil, Thailand, and Mexico. Make sure you only purchase it if there are lab tests to prove its quality. The best brands triple test theirs: At the source, as it enters the United States, and before it gets packaged.
There’s a lot more to finding a cheap medium than the initial price you pay! First and foremost, a medium that contains nutrients instantly saves you money. Let’s imagine that there are two options: A potting mix for $10 you found on sale, and a super soil mix that costs $40.
Instead, it works best if you use a multiple-watering or continuous-flow hydroponics system. HEC is sterile, inert, and doesn’t do a good job of buffering. However, it is very stable and can hold seedlings in a hydroponics system. You can also use HEC as a bottom layer for drainage in a plant container.
Overall, super soil is arguably the most expensive because the costs don’t reduce over time. You always need to buy everything from scratch. On the plus side, you don’t need extra nutrients, so those using expensive versions at present could actually save money. As you only need to add water and occasionally monitor your plants, super soil is an excellent option for the novice.
Ultimately, super soil is expensive in terms of up-front costs. However, it could save you a lot of money if you are a regular grower.
What Makes a Growing Medium Inexpensive?
However, it is inert, which means you must add nutrients, so the initial cost is relatively high. As its rate of water retention is significant, you must ensure it has adequate drainage. Rockwool also has a high pH, so you need to check the root zone regularly.
You will likely find slabs of coconut coir for a similar price as a reasonable potting mix. The primary difference is that you must also purchase nutrients. As your plants require the food immediately, it means buying added nutrients right away. Coco Coir is coconut fiber, often remaining from processing coconut for consumer goods.