MEDIUM (required field)
SOIL = Soil based mediums or soil mixes. *ALL* nutrients are to be found in the medium. They are earthen in nature. The intended use is that plain water will keep the nutrients in a form usable by plants, and that "infrequent" feeding with soluble fertilizers "may" be necessary with indoor plants in lieu of adding more nutrient rich soil via repotting.
HYDR = Hydroponic mediums are inert. *NO* nutrients are found in the medium, *ALL* nutrients are supplied in solution.
FORT = Fortified mediums are those containing nutrients (or nutrient bearing amendments) but not supplied in adequate quantities to sustain plant growth for the life of the plant. The intended use is that "regular frequent" feeding with a soluble N-P-K fertilizer containing trace and secondary elements "is" necessary. Typically this medium type is not earthen in nature and eventually requires use of hydroponic techniques. Some soilless mixes fall into this category.
TRON = Phototron, use this as a medium entry "only" if you use Pyraponics medium and nutrients. If you use a Phototron but don't use Pyroponics methods then enter either SOIL, HYDR, or FORT whichever is more appropriate.