Hemp and marijuana, both cannabis plants, are hard to tell apart. The average person and law enforcement officer can struggle to tell the difference in their leaves, buds and flowers. The two plants differ in their levels of Delta-9-tetrahydrocannabinol, or THC, the chemical responsible for marijuana’s high. Hemp typically has less than 1 percent, but marijuana can have THC levels up to 30 percent.

More important for many in the hemp industry, however, is a federal law that puts the THC ceiling for legal hemp at 0.3 percent of its dry weight. States can order the destruction of a grower’s entire hemp crop if testing finds the THC exceeds that maximum. The THC ceiling is designed to draw a clear line between the cannabis cousins, hemp and marijuana.

David Wilkinson, co-founder of The Hemp Business Advisors in Fort Collins, Colo., says he knows of several growers in 2018 who lost their crops because they didn’t make arrangements for the tests that would have alerted them that their crops exceeded approved THC levels.

A vigilant grower can harvest early if sampling indicates his crop is approaching that limit. THC levels in a hemp plant can fluctuate throughout the growing season. The timing of the sampling and the parts of the plant used can make a difference.