Hemp for fiber

I am not going to encourage anybody to break the law. And, at this time, Cannabis production/possession is still a Federal crime in the United States.

That said, there are "windows" where cannabis can be legally grown for fiber or CBD oil. There are also states, like Michigan, where cannabis has been decriminalized and state law allows individuals to grow a limited number of plants for personal use*. Those states which have decriminalized cannabis probably do not have any language that would prevent a person from growing that same limited number of plants for fiber or seeds.

If the Feds were to decriminalize "weed", this is how you might approach the issue.

Latitude

Cannabis plants are a bit like onions, latitude matters. Some seed-lines do well in the tropics. Some seed-lines might do well between latitudes 30th (Austin, Texas) and 40th (Indianapolis). Other seed-lines might do well north of the 40th parallel. Daylength is a clock that triggers many important biological processes like the binding of fibers (lignification) within the stem and daylength varies by latitude.

Scholar.google.com is a good resource for field-trials and yield information. For example, if you were to search "cannabis fiber yield data" you might learn that Kompolti was the top cultivar for fiber but worst for seed production in Alberta, Canada field trials. or you might learn that Ferimon performed well in Quebec. Han-NE seems to perform well through a wide range of latitudes but it is a "bushy" plant and the hank of fiber is more of wad-like than the long, non-tapering strips from Ferimon.

Pollination

Most fiber cultivars are sold as "non-feminized" seed. Some cultivars have both male and female flower and are self pollinating. If you grow any quantity of either, they will put pollen in the air that will cause THC or CBD producing plants to set seed and stop flowering. The people growing those plants will be very, very angry.

Timing harvest

The fiber is strongest and easiest to extract when the male plants first start to pollinate. That forces you into a decision: Are you growing for seeds/oil or are you growing for fiber? Additionally, planting to maximize fiber production involves planting the seeds much more closely together while seed production has much lower seeding rates per acre. 

Growing fiber plants "legally"

There is a lot of red-tape involved and, at least in Michigan, you must grow at least an acre and you can expect to be visited by state officials at least twice during the growing season.

*In Michigan it is legal to grow up to 12 plants of cannabis for personal use. My wife could grow an additional 12. The plants must be enclosed and the entrance must be locked. The plants must not be visible from the road or adjacent driveways. I was told by a semi-reliable source that you can rent out part of your enclosure to other adult, Michigan residents who wish to grow cannabis but it behooves you to have paperwork clearly identifying the extra plants as somebody else's property. My semi-reliable source suggested that "share-cropping" was a common method of compensation via the minor quantities gift provisions of the Michigan cannabis laws.

Personally, it would be such a pain in the behind that it would not be worth my time, and the fact that it is still a Federal crime.