Hemp production increased During World War I [1914-1918] when imported hemp and natural fibers became unavailable. Kentucky farmers returned portions of their to hemp cultivation for army shoes, twine for grain bags, rope for rigging and caulking for ships.
Prices soared, rising from $160 per ton in 1915 to $250 early in 1916, and hemp seed, which was scarce, sold "at the unheard-of-price of twenty dollars a bushel."
The U.S harvested a total of 4,200 tons of hemp in 1915, followed by 9,300 tons in 1916, and 20,600 tons in 1917. In Kentucky 6,500 acres, 13,500 acres, and 18,000 acres respectively were planted to the crop each year from 1915 to 1917 inclusive. During the same time the total acreage of the entire country doubled annually, reaching an estimated height of 42,000 acres in 1917.
"From a position of insignificance," wrote a student of the industry in 1918, "hemp has become within the past few years a crop of national importance - second only to cotton as the greatest fiber crop of the United States." From it came "thread for army shoes, twine for the grain harvest, calking for ships - surely hemp should be reckoned among our foremost war crops."
The war had furnished the stimulus for the increased production, but that growth largely had been made possible by the introduction of machinery designed to perform the expensive and burdensome tasks connected with hemp culture. Unfortunately for the future of the industry in Kentucky, most of the farmers in that state continued to depend on inefficient hand labor, which turned out a product inferior to the "long line fiber and tow" produced by the breaking plants which had been erected in Wisconsin, Ohio and Indiana.
---
Source
Hopkins, J. (1951). A history of the hemp industry in Kentucky. University of Kentucky Press.