Grow Media-
Growing medium is the material in which plants grow.
Outdoors, soil is almost always the medium. But in an indoor garden, growers can choose from a variety of media, each with attributes that offer specific benefits to the plants and/or the grower.
Of course, indoor growers can use soil in pots, but many prefer lighter natural materials such as peat moss, coir (coconut husk fiber), or bark chips. In advanced hydroponic systems, clay pebbles, rock wool, stones or gravel, plastic foam, and perlite or vermiculite are popular options because they hold plant stems securely but drain quickly so the roots are not sitting in water.
Unlike soil, the other grow media don’t supply the plants with any nutrients, so the grower must provide them.
Soil
Soil is the most common grow medium. Cannabis does best in loam soils. Loam soil is composed of almost equal amounts of sand and silt with a little less clay. A good ratio is 40 percent each of sand and silt, and 20 percent of clay. Loam holds nutrients and has a texture that retains water long enough for plant roots to access it, yet it drains well, meaning that the water eventually seeps away so that plant roots do not sit in water and rot. Without quality soil, plants struggle to survive and usually require supplemental feeding and watering.
Among loam’s three components—sand, silt, and clay—the sand particles are the largest. Sand does not hold on to moisture, but it provides good aeration and drainage.
On the opposite end, clay particles are much smaller and are easily compacted. That makes clay a great material for building bricks but not so great for allowing water, air, and plant roots through. However, clay tends to be higher in nutrients than the other soil components.
Silt is the medium-size particle with better moisture retention than sand but fewer nutrients than clay. Silt helps clay and sand mix together more readily, somewhat like tempering chocolate.
In addition to providing nutrients and water effectively, loam has a loose and crumbly texture (friable). Loose soil provides room for oxygen to be present in the soil, which is also necessary for root growth. The friable nature of loam also makes it easy for roots to spread out to consume nutrients and water.
Turning your existing soil into loam is an ongoing process that involves incorporating organic matter into the soil every year. The decomposing organic material creates the well-draining conditions plants need. Organic matter also attracts beneficial organisms that keep the soil healthy and alive. Shredded leaves, straw, and finished compost work beautifully to create rich, loamy soil as they decompose.
Organic matter depletes quickly as it decomposes. This is why you must amend the soil each season, preferably in the fall. How much organic matter to add depends on how out of balance the soil is.
Soilless Grow Media
Soilless grow media are composed of inert (non-soil) ingredients like coco coir, perlite, peat moss, rockwool, and vermiculite. These can be a great choice for growing marijuana.
When growing in a soilless medium, you can treat your cannabis plants almost the same as if growing in soil. The main difference is you feed all their nutrients in the water.
Although there are many different possible soilless ingredients, the most popular grow media for cannabis contain significant amounts of coco coir and perlite. This combination seems to work especially well for growing cannabis. As a result of coco’s growing popularity, other types of soilless mixtures (especially the peat-based ones) have become far less common in cannabis grow rooms over the years.
Even when it comes to soil mixes, you still often see both coco and perlite in the ingredient list, because they help improve the overall properties of the soil.
Hydroponics
When people are talking about hydroponics, they’re usually referring to growing your cannabis with the roots sitting directly in water. The most popular style of hydroponics for cannabis plants is known as Deep Water Culture (a.k.a. DWC), and it has a very popular variant known as “bubbleponics” or a top-fed Deep Water Culture (DWC) system.
DWC is one of the few types of hydroponics that can support larger plants. Other types of hydroponics (for example NFT or Aeroponics) have a difficult time growing plants as big and nutrient-hungry as cannabis.
Hydroponic substrates do not contain nutrients. The grower is responsible for feeding the plant through a nutrient solution in the water. The roots are in constant contact with water; the growing media is nothing but a substrate for the plant to develop a root system. This gives the plant structure and keeps the roots away from light, making them believe they’re underground. It provides great oxygenation for the root system, leading to robust health and more efficient nutrient uptake.
Media like perlite, gravel, sand, and volcanic rock have been widely popular in hydroponic grow rooms. But with the increasing popularity of the method, new substrates have appeared on the market. Mediums like clay pebbles, rockwool, perlite, coco coir, and mapito are now being used and experimented with. Below, we’ll approach these substrates in greater detail.
Clay Pebbles
This is arguably the most popular growing medium in hydroponic operations nowadays. These small, brown spheres provide excellent oxygenation for the roots. This way, they tend to grow amazingly if proper irrigation is provided. The roots aren’t placed under any stress and grow easily, making nutrient absorption extremely efficient. Make sure you find some that are already washed and have been adjusted for pH. This way, you won’t have to worry about these steps later, which is a very tedious process.
Rockwool
An excellent insulating material and very popular in hydroponic grows, rockwool is an awesome medium for your cannabis to grow in. It has great oxygenation as well as water retention properties. Although, it takes experience and time to get everything up and running. Before placing your germinated seed, the pH of the slab must be around 5.5. To do this, immerse the rockwool in a nutrient solution with a pH of around 4.5 and an EC (Electric Conductivity)/ nutritional value of 0.5-0.6. This process should take around 24 hours. If the pH is not at the desired value by then, immersing the slabs again will be necessary.
Coco Coir
Popular amongst Asian grow operations, coco coir results from natural waste of coconut plantations. Coco Coir is made from the outer shell of the coconut. It’s renewable, holds moisture better than soil, and absorbs water very efficiently. It even contains naturally present nutrients, a neutral pH value, and is usable for up to 5 years. It’s an excellent option for indoor grows as it does not develop fungi, even though it retains water for a long time.
Perlite
This is a mineral that, when heated to a certain temperature, expands to several times its size. Perlite is relatively inexpensive and easy to use, therefore it’s a popular option as a growing medium. It has excellent aeration and retention properties. Perlite is non-renewable, although it is reusable. This is important for environmental concerns, yet its long life cycle can help cancel out the non-renewable factor. It is a medium that will not degrade or decompose, remaining usable for years. It has a neutral pH, which will take on the acidity or alkalinity of a desired nutrient solution.
Mapito
Popular amongst Dutch growers, mapito is a mixture of rockwool and coco coir with great oxygenation and moisture retention. Treat the medium before placing the seed in a similar way to the rockwool method mentioned above. The substrate should be placed in a bucket of water with an EC level as low as 0.3-0.4. This medium comes in flake form, which brings several advantages. Contrary to the rockwool and coco coir bricks, mapito allows the grower to move the plants. It becomes easy to pick up the flower from the vase to check the root system or move into a larger pot.
Mapito’s flakiness provides excellent oxygenation and retains and absorbs water efficiently. But the fact that it’s looser also means that you can’t press it too hard when getting it into your net pot. This may cause stress on the roots with the added difficulty of trying to pierce through the material.
