If you choose to mix your own organic soil, then it will not need any additional amendments because it is already properly prepared. As mentioned, getting the correct formula can be challenging, so be prepared to take some time to get this right.
For potting soil, consider mixing it 80/20 with perlite to make the soil less dense. While this means you will need to water more frequently, it gives the roots plenty of “elbow room” to spread out.
Coco coir doesn’t require perlite, but depending on the manufacturer, it may need to be “pre-rinsed” before use to wash away any accumulated dirt or dust from the manufacturing process. Generally speaking, the better suppliers have already rinsed the product. Coco coir also tends to require more calcium and magnesium than potting soil, so consider adding a bit extra to your regular feeding schedule. As a bonus, you can purchase coco coir in expandable bricks, which makes transport and storage more convenient.
When you are ready to experiment, there are a wide range of soil preparation additives you can consider, including B1 Complex, root enhancers, and soil enzymes.
You need someplace to put your weed growing soil! For indoor growing, a 3-gallon container is fairly standard. Larger containers lead to taller plants, which can be a problem indoors. However, if you are willing to use cultivation approaches like a Screen of Green or Supercropping, you could use a bigger container.
For outdoor growing, if not in a garden bed, you will need at least a 5-gallon container, or larger if possible. Your plant will grow very tall and could easily tip over if your container size is too small. Consider weighing down your container by putting a layer of gravel in the bottom before your medium. This will also help with drainage.
Recently, fabric containers (aka air-pots, smart-pots, etc.) have become trendy for both indoor and outdoor growing. They use a technique called “air pruning” to prevent the plant’s roots from circling the inside of the container. This is supposed to lead to better growth, but the evidence is not conclusive.
So, there you have it. Hopefully, our guide has taken some of the guesswork out of choosing the best soil for marijuana growing. The last bit of advice I can offer is to try and limit the different elements, keep things simple, and don’t fall into the trap of always trying something new. Stick with what you know, and I can almost guarantee you will have a great grow.