You can find many premade soilless planting mixes for growing marijuana that you can use together with an organic nutrient-water solution. Retail nurseries sell a number of grades of potting mixes including those that have added organic fertilizers already. Some might also have water-holding crystals. Many of these mixes are made from peat moss or forest products (i.e. compost, bark, and other forest material).
Sand, perlite, organic fertilizers, and compost are also likely to be in the mixes. A few of the enriched mixes have enough nutrients to support the plants in 10- or 12-inch diameter containers for three to five weeks. This is enough to get them through the second stage of vegetative growth at which point the marijuana plants have produced a well-developed root system. Even so, some plants in enriched mixes grow larger at an increased rate when they are provided with water-soluble fertilizers. Cheap mixes are generally just a mixture of peat moss, bark, and textural amendments that have very few nutrients. When using these mixes, the plants are fed only through the water-nutrient mixture.
Every mix composed of organic ingredients decomposes when exposed to nutrients. Microorganisms chow down on the combination of fertilizer food and carbon found in the planting mix. Even so, the medium acts as a buffer that first absorbs and then releases nutrients. Planting mixes are thus more forgiving than straight hydroponic mediums like lockwood or clay pellets. You can find a number of water-soluble organic fertilizers on the market. They should be supplied any time the marijuana plants are irrigated.
You didn’t say anything about how wide or tall the plants get by the time ripening occurs. Regardless, the strongest most productive soil-grown marijuana plants need to have about 0.5 to 1 gallon of soil for every foot of height the plants grow. Broader, more branched plants require more soil.