Cannabis plants have a great capacity to adapt to different growing mediums, what gives growers great advantages, as it can be grown in many places, and types of substrates. In this post we will talk about different substrates for cannabis, in addition to mention best substrates for cannabis indoors and outdoors.

Which are the most frequently used cannabis substrates?

To understand what substrates are better for marijuana growing the first we need to do is explain which are the most frequently used by average grower nowadays. We will also detail characteristics and differences of each one, besides citing some tips for growing.

Soil for cannabis

Soil is the oldest type of substrate, as it’s been used for centuries, since prehistory when human being stopped being nomad and became living in a sedentary way, growing the ailments needed to survive.

Soil itself is a substrate created by a mix of different compounds, that once mixed turn to be named as soil. It can be presented in different compositions (and of those compositions depend how suitable it is for some species or others). In this case, talking about soil for cannabis growing, we seek for a structure and composition that better covers marijuana plants needs so it can develope in its full potential.

What are the main compounds of a soil for marijuana growing?

Now we step forward into compounds for good cannabis substrate, the first we should know is what are the basic needings of a cannabis plant, to “build” our substrate with full knowledge, avoiding this way problems that could turn into lack of nutrients, nutrientlocks, malformations or, in worst cases plant’s death.

The first detail to figure makes refference to roots, as root system of plants is the base onto build all aereal structure, so one of the most vital points for plant’s developement. If we pretend our roots to grow and colonize the substrate, it is important to avoid growing in a soil too compact, or with compacting trends, as our root system will need to battle against a substrate that doesn’t favor its growth. In general to avoid growing in substrates with clay is important, as clay acts as waterproof that prevents water pass through and drainage, what derives in high possibilities of suffering from root rot, in addition to lack of root system oxygenation.

Specially if we want to enhance a good aeration of root system, we should look for a spongy soil, as more spongy the soil is easier for roots to survive, and colonize the substrate without problem.

If we pay attention to major brands specialized in cannabis soils, we notice which are the main and most used compounds to create a good soil structure: White peat, black peat, bark, coco fiber, worm castings and perlite.

Peat: Peat is organic matter that forms an spongy mass but light, very rich in carbon. While white peat has more content of organic matter, black peat has less content, but is more mineralized. Its major benefit is based in its high water holding capacity, so it is important to know its origin as composition and pH value can vary from one to another.

Bark: Is sourced from stems and roots from trees like pine, being a natural material that prevents water evaporation, what helps keeping the substrate’s moisture, increasing aeration and pad.

Coco: Coco fiber is an inert substrate sourced from coco shield, that can be introduced in different sizes and volumes. It has many benefits, as it improves soil structure making it more spongy. Another good point of adding coco to your substrate is it gets to improve the structure without modifying the pH nor EC of it.

Worm Castings: Worm casting is an organic substance of earthy look, derived from decompost of worm’s organic matter. It sources humic acids to substrate, feeding it, and helping to regulate vegetable nutrition regulation.

Perlite: Perlite is silicium that has its main virtue in the fact that doesn’t absorb water, it just keeps it in the surface, making it available for surrounding roots. Improves sponginess, drainage, in addition to help avoid evaporation of water (when placed in surface of substrate).

Vermiculite: vermiculite is a mineral formed by silicates of iron and magnesium, not as used as perlite, but it also has many and good benefits when mixed in substrate. One of its major benefits is the fact that it has great thermal insulating capacity, what in summer could help a lot in outdoor cannabis gardens. It is so light, lasts forever, and has a neutral pH value (pH=7,2) what almost keeps the pH of substrate unaltered.

Clay: Clay pebbles (clay) is another compound frequently mixed with substrate, in this case to bring in aeration, and improve substrate’s draining capacity. Clay pebbles are volcani lava rocks covered with clay, what brings in a rigid compound that holds soil, besides letting water flow when there is an excess.

EC levels of soil

When we talk about EC levels of substrate, we are referring to the amount of nutrients it contains. These data gives growers interesting information about how suitable a substrate is for a certain stage of growth.

Even though is true most comercial soils for cannabis contain slow-release fertilizers (they slowly release as weeks go by), it is also true that a part of the minerals contained are quickly available for plants, and we don’t want this quick uptake to cause a nutrient-lock (specially during first stages of vegetative stage, when plants are weak, and demand lower amounts of nutrients).

To solve this issue most reputable brands offer different types of soil (more or less fertilized) so grower can germinate his seeds or seedlings in a low fertilized soil, and further on transplant to a bigger container with heavier fertilization.

In general, in any bag of soil from a trusted company will appear not only compounds of that soil, also the EC value of substrate (understanding an EC=1,6 or lower as soft pre-fertilized, and EC=1,8 or higher as heavy pre-fertilized).

Types of soil depending on nutrients contained

Soft: Lightmix Biobizz, Lightmix Plagron, Terra Professional Canna.

Medium: Growmix Plagron.

High: Allmix Biobizz, Allmix Plagron, terra Professional Plus Canna, Bio Terra Plus Canna, Batmix Plagron, Royalmix Plagron.

Types of soil depending on pre-fertilization

We’ve spoken about different nutrient levels of each type of soil, but there is another hotspot to note when using one or another soil: How has it been hydrated or pre-fertilized?
We do understand pre-fertilization as all fertilizers sourced further more its compounds. Even this concept can sound rare, it is used to know how a substrate has been hydrated before being packed. Remeber that even in low quantities, all substrates in market come more or less hydrated to keep them in best conditions until the day it’s used.
This is a key point, as in many cases, the nutrient solution used to hydrate the substrate contains synthetic nutrients (mineral), what crashes with the will of many growers who just want organic nutrients to get a 100% organic crop). If you are one of those, don’t panic! There are options that guarantee a 100% organic pre-feeding of soils for organic farming.

These are few examples of 100% organic soils for sale: Lightmix Biobizz, Allmix Biobizz, Royalmix Plagron, Batmix Plagron, and Canna Bio Terra Plus.

¿What does Supersoil Mean?

In a previus post we deeply explained everything about Supersoil, a soil composition that is acquiring interest in-between growers, that takes a base of comercial soil, to which we add different compounds that improve soil feeding, turning it a full-cycle soil, that doesn’t need to be fed. If you want to learn more about this type of soil do not hesitate to read our article talking about No-till cannabis.

Substrates for hydroponic growing

Growing hydroponics has increased attention of growers along last years, not only for its results, also for the final quality of the crop, source optimization, being a discreet and clean system. One of the main characteristics of hydroponic systems is they use an inert substrate (no life contained), so grower must control from the first day of growing until harvest all feeding parameters as well as pH and EC of nutrient solution.
The reality is those parameters also should be controlled in our soil gardens, but characteristics of hydroponic gardens make it a must, while in soil it is only recommended.
The most widely used substrates for hydroponics are: Coco, Clay pebbles, Rockwhool and Mapito.

Growing hydroponics in Coco

In-between existing substrates for hydroponic growing, coco is probably the closest to soil, so the one that forgives more errors from growers. As we previously commented this is compound of coco fiber with different sizes (depending on its size it will have more or less water retention). The greatest advantage coco fiber offers is the substrate will dry quicker, what favors higher amount of waterings (so more control over our plant’s feeding).

Another advantage it brings is it’s a very spongy substrate, it is so difficult (almost impossible) to drown seeds due excess water (something very common in soil when growers irrigates too often). Notice it is important to don’t be overconfident, because even though roots can hold all that amount of water regularly, what do can happen is to let pathogen fungus to appear, what could harm plants.

For last, but not least, being coco a spongy substrate it is so easy for roots to colonize it, deriving in a root expanse much quicker than it happens in soil, becoming in less vegetative days needed to get plants big enough before flowering.

As we explained, being an inert substrate, is the grower who must feed plants with the proper amount of nutrients for each stage of plant’s cycle, as it does not contain any mineral. Is here where the first choice should be made: Organic nutrients or synthetic fertilizers. Our personal choice is to use organic fertilizers that favor a higher quality crop, but note this is just a personal preference.

Coco fiber lets you to feed it (and great large crops) using mineral nutrients formuled specifically for plants grown in coco. Almost all brands of nutrients offer a range of products for coco, maybe with some overstanding to others like Canna Coco A+B, which is probably the best fertilizer for plants grown in coco.

Arrived to this point lets explain something about bad aspects of coco: Obviously it is a must to control pH and EC values of your nutrient solution. PH becase plants grown in coco are more susceptible to pH variations, and EC because they are also susceptible to the amount of nutrients dissolved in water and the retention in substrate.

Advise: If we pretend to grow our first plants we aim you to choose soil instead of coco, as it will forgive more errors, what will derive in larger crops (the key point when first time growing).

¿What formats of coco fiber can I buy in a grow store?

The most common format of coco you’ll find are 50L bags, available in most grow stores. Examples like Biobizz Cocomix, Plagron Cocos Premium, Canna Coco Professional Plus or Canna Coco Natural. It is worth to find differences in-between them, as some like Canna Coco Professional Plus contain mycorrizae that improve growth ratio and final yields (being our recommended choice).

We can also find out what’s called Coco Slabs. Slabs are plastic bags filled with coco fiber, that are ready to use as a container itself. Many growers place those slabs directly in trays with drainage, and make some cuts in the surface of the slab to place plants in. This way both install and claening after growing cycle are much quicker, without damaging the system efficiency.

Coco bricks: Another option is purchasing coco bricks, that are coco fiber blocks, pressed and dehydrated. This format makes easier to transport substrate, reducing the volume and weight of it. Once we bring it in our garden, we only need to hydrate the bricks with nutrient solution (containing a low amount of nutrients so plants can uptake it once we place them in substrate). As it happens with bagged coco, there are many brands available in grow stores that sell coco bricks, like XL Rhiza UGRO (our favorite and probably the best buy for its quality, and also for containing mychorrizae) or Plagron Cocos Brix.

Growing hydroponics in clay pebbles

Clay, or clay pebbles, is one of the most used hydroponic substrates, as has been sold and used by many brands and systems as a growing medium for decades.

As we explained previously, clay is an inert substrate, produced within volcano rocks covered with clay. Usually it is shown in format of little spheres (with bigger or smaller size depending on each manufacturer) that give as main advantage a medium in which roots are totally in contact with water, so the root system can expand extraordinarily fast.

The first we should do if we’ll use clay in our garden is to clean it and adjust its pH value. To proceed with the cleaning the easier way is to own two large plastic tuppers. The first one will be used to clean the clay, so we’ll make some holes on its bottom to let all water used can drain. The second will be used to adjust the pH value once the clay has been cleant). Once our clay pebbles are clean we place them in a large plastic container, fill the container with RO Water enough to cover the clay, and then adjust the pH value to 5,5-5,8. After a couple of hours in this solution we’ll check the pH value is still on desired value (adjusting it again if it has changed) to pour the clay again in the first plastic tupper. Once the clay is clean and pH adjusted, we can proceed to use it.

Note: Never do these operations in you tub. You won’t be the first to muffle your tub drain system with the consequent economic problem.

Most of the systems using clay pebbles are based in a closed-system of water impulsed by a pump that creates a continuous movement, having a tank in which the water solution is stored. In hydroponic systems is very important to daily check the pH and EC of your nutrient solution, as small differences in these values can cause plant’s death.

Another key detail is replace the water of your reservoir once per week even if the solution has not been uptaken. Many growers see in hydroponics a very efficient system that doesn’t waste water at all, and that’s not 100% true. It is true that in a closed system all drained water comes back to plants again and again, but it is also true that after some days recirculating , water parameters have changed enough to compensate the waste and refill the full tank with new water and nutrients.

To this recommendation of substitution of water every week, we must add the differences in plant’s needings depending on each stage of growth, so it is almost a must to change your solution once per week.

Advise: Being a system in which roots precise of water flow to survive, growers must check everyday that water is still circulating, because if the system fails plaants could suffer and even die (specially when they are in advanced stages and plants require larger amounts of water. We like to mention this point to clarify to all growers that an hydroponic system can be everything but autonomous. You must go there everyday at least to check everything is going its way properly.

Rockwhool as marijuana substrate for hydroponics

In our list of possible substrates for hydroponics rockwhool is another popular choice. In this case is not only used as growing medium, it is also used combined with other growing mediums, as rockwhool is a medium used by many growers producing their own clones (that further on are place in soil, coco, and also in clay).

Wockwhool is a very clean substrate, lightweight, and easy to colonize by root, that needs a previous adjust before being used, but that offers great results when growers know how to use it.

Before begining to use rockwhool, the first we recommend is to clean it, adn adjust its pH value. Clean it because during the manufacturing process (specially the cut) a dust is created, and is recommended to remove it before use. Adjusting the pH value is also important, as it happens with clay, if we pretend to avoid plant’s shock when placed in medium.

To adjust pH value of Rockwhool the best we can to, and the easier way to do it is place the rockwhool cubes, or slabs (or whatever the format is) in a large plastic tupper, fill it with RO Water and then adjust the pH of that water to pH=5,5. If after some hours we check the pH again and it has changed we should adjust it again. If not, we can proceed to use it.

What formats of rockwhool can I purchase in a grow store?

Rockwhool is commonly found in two main formats: Rockwhool cubes, or rockwhool slabs.

Rockwhool cubes: Usually available in different sizes, depending the choice on the size of the plant we pretend to place in. If we’ll place a seedsproud, or seedling we should use the smaller sizes (that later we’ll transplant to bigger ones).

Rockwhool slab: Rockwhool slabs are sold in the same format described with coco slabs (in plastic bags that can be used as pot itself). Every slab of rockwhool is usually 1 meter long by 15 cm width, being ideal to place them in trays with drainage thoughts for this purpose. Other growers use bigger systems with big trays (also with drainage) to place 5-6 slabs per squared meter. As we said every slab must be pH adjusted before placing plants in it. Once cleant most growers place 4-5 plants per slab to create a Sea of green of 20-30 plants per light.

Mapito: An alternative substrate for hydroponic systems

We let Mapito appear in last place, as this is not a new type of substrate (basically is cut rockwhool), and because its use is still very rare compared with any of the other ones mentioned. In general mapito is used to fill pots to use them like conventional garden (being possible to use automated irrigation systems, or a flood and drain system).

As we just said, is basically cut rockwhool, so before using must be cleant and pH adjusted (the same way we do with rockwhool) to balance it to pH=5,5.

Even though many brands tell that Mapito can be reused, we highly encourage to don’t follow their instructions, as salt accumulations in it after a growing cycle are so high, and also because removing roots from it is almost impossible (and obviously not recommended).

Aeroponic growing without substrate

Before this point we’ve been explaining different substrates we can use to grow cannabis, but… Is it necessary to grow cannabis in a growing medium? No, it isn’t. there is what’s called aeroponic systems, in which roots are exposed to air, without any contact with a growing medium.

In these more advanced and professional systems roots are fed by a continuous nutrient solution spray that enhances its growth, and the viability of plants grown. These are very clean, but demanding, systems not recommended for those less experienced growers, that requires full control to get positive results. If grower makes his job it will result in a high quality crop that can get very high return, but if whatever happens, it is easy to loose our crop and all our efforts will be or nothing.

Important to mention that 3 elements are a must: Reverse osmosis water, pH meter and EC meter. If you can’t afford them, don’t waste your time in aero systems.

For those that do have these necessary tools, and are decided to jump into aeroponics a special mention: These systems demand a lot of attention, and are far away from autonomous. Every single detail must be controlled daily, and solved instantly. Otherwise will get more pain than happiness.

Conclusion: We’ve tried to explain with details and examples every single substrate for cannabis we think are more viable. If you still have doubts about which substrate to use, our final recommendation is always choose the easier, so in first place we should always think about growing in soil.

The main reason is because it is the most natural substrate, so it will be easier to get better results in terms of quality and quantity.

The second reason is because we can use organic nutrients and boosters, what guarantees an organic crop, healthier for consumption.

The third reason is because if you have a doubt it is always better to make your life easier (growing plants indoors and outdoors turns into enough “problems” to complicate it from the begining.

Said this, following these lines you’ll find a comparative table with best substrates for cannabis, advantages and disadvantages.

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