Many if not all US-based hemp cultivators grow hemp outdoors in soil. When growing hemp for the purpose of creating Hemp or industrial products, a massive plot of land is required, usually measured in hectares. Since industrial hemp is an excellent bioaccumulator (extracts and retains many compounds from the soil), it’s important to grow hemp on tilled land with safe levels of heavy metals.
Growing the right variety of hemp is important, two main strains in the industrial market exist, finola and carmagnola. These strains vary from the growing cycle to the quantity of Hemp present to the environmental conditions required to grow the variety of choice.
Unfortunately, both strains don't like to grow 20 degrees above or below the equator, these environments are too hot for most varieties. Research is currently being conducted at many institutes, primarily, the University of Florida's agricultural programs to identify heat tolerant generations in the two main strain generations. This is just one factor, another important factor is producing these strains for specific industrial purposes such as cannabinoid extraction or industrial shiv for rope, building materials, fabric, etc...
Ever since Gregor Mendel had his experiment with pea plants identifying phylogenetic traits being dominant or recessive in pea plant generations. Botanists everywhere have been using some form of this genetic engineering to create plants better suited for the environments we want to grow them in. The pharmaceutic industry uses a much more complex approach with tobacco plants being able to incubate specific types of drug actives they will then use to create medicines. Hemp will only become stronger in hot, arid environments and more valuable to us with higher concentrations of cannabinoids with genetic research.