There are two main drivers for the increased interest in growing marijuana organically. One is concern for the environment and over the long-term impact of synthetic chemicals. The other is the fact that we are what we eat (or smoke) and that ultimately any chemicals used on marijuana plants will quite possibly find their way into our bodies. This is a particular issue for medical marijuana users. Some proponents of organic growing argue that organic growing offers better results in terms of yield and/or taste but there is still a lack of hard evidence to support these claims.
For those interested in organic growth there are basically two approaches. One is to buy organic soil and organic nutrients from garden suppliers and just use them out of the box as it were. This has the advantage of simplicity and convenience, but, of course, is more expensive than making your own “super soil”.
The most straightforward way to enrich any soil is with compost, organic or otherwise. A rule of thumb for creating a good compost is about a quarter nitrogen-rich material, such as grass clippings or manure, half green ingredients (this is a great way to use up kitchen peelings and such like, coffee grounds are also a good addition) and a quarter woody material (this can include shredded newspaper, or alternatively dry leaves or wood chips). In the old days, making compost meant measuring the temperature with a thermometer and moving around the material with a pitchfork. These days, more advanced composting bins which can make life much easier. There are also twists on standard composting approaches such as bokashi bins and wormeries.
If you want to take composting to the next level, you can brew compost tea. The very simplest way of doing this is to fill a bucket 1/3rd full of compost, then fill it up with clean (i.e. unchlorinated) water. This may mean using filtered water. Let the tea brew for 3 to 4 days stirring once or twice a day. Strain the resulting brew and dilute the liquid until its the colour of tea. The solids can be used for any gardening purpose or can be recomposed. The liquid should be applied immediately. If growing outdoors, aim to schedule the straining process so that you're applying the liquid in the early morning or late evening.