Industrial Hemp Farming in the US: Rules and Agronomy

Growing industrial hemp in the United States is legal, but only under a license or authorization issued through a state hemp program, a tribal hemp program or the USDA hemp program. Which program applies depends on where the growing site is. Hemp is grown for fiber, for grain and for cannabinoids, and industrial hemp means the crop grown for stalk, fiber, grain, seed oil and similar non-cannabinoid uses. The federal definition of what counts as hemp is in the middle of a change. Anyone planning a first season should settle the legal questions before ordering seed, and should check current rules with their state department of agriculture (or USDA where there is no state or tribal plan), because the federal definition is changing and dates have already moved once.

What hemp is in federal law

Until 2018, hemp was treated as marijuana under the Controlled Substances Act. The Agriculture Improvement Act of 2018, the farm bill known as P.L. 115-334, removed hemp from the definition of marijuana and defined it as cannabis with a delta-9 THC concentration of not more than 0.3 percent on a dry weight basis. Hemp stayed subject to USDA and FDA regulation.

In November 2025, the FY2026 agriculture appropriations act (P.L. 119-37, enacted November 12, 2025) amended that definition. Once in effect, the 0.3 percent dry-weight limit applies to total THC, including THCA, not only delta-9 THC. The new definition explicitly includes industrial hemp grown for stalk, fiber, grain, seed oil and similar non-cannabinoid uses, and it excludes viable seeds above the total THC limit, intermediate products above 0.3 percent total THC, and final cannabinoid products with more than 0.4 milligrams of THC per container.

The change was to take effect November 12, 2026. The Continuing Appropriations and Extensions Act, 2027 (P.L. 119-103, September 2026) delayed parts of the new definition to December 11, 2026; the exclusion of products with cannabinoids not naturally produced by the plant still takes effect November 12, 2026. Rules and dates may change again. Check current rules before planting.

The license, the background check and the paperwork

A grower must be licensed or authorized under a state hemp program, a tribal hemp program or the USDA hemp program. Where the state or tribe has no approved plan, growers apply to USDA through its online Hemp eManagement Platform, and USDA accepts applications year-round, according to the USDA Agricultural Marketing Service.

Two federal rules sit behind the license. A person with a state or federal felony conviction relating to a controlled substance may not produce hemp for 10 years from the date of the conviction (7 CFR 990). And USDA licensees report hemp acreage to the USDA Farm Service Agency within 30 days of planting, with the location of each lot (7 CFR 990).

The sampling and testing sequence has its own page: hemp licensing, pre-harvest sampling and THC testing sets out who samples, what part of the plant is taken, and how the laboratory reports the result.

Three crops under one name

Hemp for fiber, hemp for grain and hemp for cannabinoids are grown very differently, and a plan built for one does not transfer to another. Grain and fiber types are taller, grown through to seed, and planted at very high populations, as high as 500,000 to 1 million plants per acre, according to Oregon State University Extension. Cannabinoid types are grown from transplants or seed at far lower densities.

Season length separates the cannabinoid types further. Full-season, short-day types use nearly the whole season, 120-140 days, and can be 5- to 7-feet-tall with up to a 5-foot diameter depending on spacing. Autoflower, day-neutral types finish in 70-90 days and stay 2- to 3-feet-tall with a 1- to 2-foot diameter; in southern Oregon they can be harvested by late July, avoiding the highest water demand.

The season, from setting plants to the sample

Mature hemp tolerates a light frost of 29-32°F that would kill seedlings in spring, so transplants go out after the danger of frost, and harvest ideally comes before the first hard frost, according to University of Vermont Extension. Whether to raise transplants or sow directly is a separate decision with its own trade-offs in labor, root disturbance and timing; hemp transplants versus direct seeding walks through it.

Plant density and water are the two levers that shape the canopy. Oregon State University Extension’s figures, for cannabinoid types, are a starting point rather than a universal rule: widely spaced plantings have generally run 2,000-4,000 plants per acre on drip tape under plastic mulch, while a 6-by-5-foot spacing is only about 1,500 plants per acre. Above about 9,000 plants per acre, roughly 2.5-by-2 feet, full-season types reach high biomass. Autoflower types are not crowded until closer than about a 2-by-1 foot spacing, or 22,000 plants per acre or more. Wide spacing gives more side branches per plant; dense spacing gives more total flower per acre. Equipment and mulch width often decide the layout. Hemp spacing and irrigation basics covers the layouts and the water response in semi-arid southern Oregon, where flower yield of cannabinoid types rose with irrigation up to about the crop’s seasonal potential evapotranspiration and then leveled off.

Dense plantings in humid climates or under overhead sprinklers raise the risk of powdery mildew and gray mold. Drip irrigation and enough spacing for air movement help.

Harvest timing is both an agronomic and a compliance decision. The official pre-harvest sample must be taken no more than 30 days before the anticipated harvest, and total THC rises as flowers mature. Hemp harvest timing and the pre-harvest test explains how the sampling window and the crop’s maturity have to be planned together.

What goes wrong

Planting before the license is in hand. The license or authorization comes first, and the acreage report follows within 30 days of planting for USDA licensees. A crop in the ground without the paperwork is a problem no agronomy can fix.

Treating the federal definition as settled. The 2025 change to a total-THC limit was delayed in part to December 11, 2026, and the exclusion for products with cannabinoids not naturally produced by the plant still takes effect November 12, 2026. A plan written around last season’s rule may not match this season’s. Check current rules with your state department of agriculture before planting.

A lot that tests hot. A lot above the acceptable hemp THC level must be disposed of or remediated under the plan’s procedures. A test above 0.3 percent is not a negligent violation if the grower made reasonable efforts and the plant did not exceed 1.0 percent total THC on a dry weight basis, but three negligent violations in a 5-year period make a producer ineligible to produce hemp for 5 years (7 CFR 990).

Assuming the lab question is closed. USDA is delaying until December 31, 2026 enforcement of the requirement that hemp be tested by a DEA-registered laboratory. Confirm the current testing requirement with the state department of agriculture before harvest, not after.

Mixing crop types in one plan. Fiber and grain populations, cannabinoid spacings and autoflower timings are different systems. Irrigation results from cannabinoid trials do not carry over to fiber and grain types, which respond differently.

Crowding in humid weather. Dense canopies and overhead irrigation invite powdery mildew and gray mold. Air movement is part of the plan, not an afterthought.

Harvesting past the window. The sample must come within 30 days of the anticipated harvest, and THC continues to rise as flowers mature. Late harvest narrows the margin for compliance.

Before the first season

Work through the legal frame first: confirm which plan covers the site, apply for the license or authorization, and read the current version of the definition and the testing rules with the state department of agriculture. Then choose the crop type, set the population and irrigation layout to match it, and put the sampling date on the calendar before the plants go in the ground. The agronomy is manageable; the calendar and the paperwork are what catch first-time growers.