More than half of hemp crops cultivated in Hawaii in the past year were unusable due to high THC levels, officials said.

The crops cultivated for the state's hemp industry tested above the federal limit for the chemical that causes people to become high, The Honolulu Star-Advertiser reported Monday.

Eighteen crops were destroyed because of heightened tetrahydrocannabinol, or THC. The state Department of Agriculture granted waivers to four crops that tested slightly above the limit, allowing the plants to be used as hemp.

A cannabis plant containing 0.3% or less THC is legally classified as hemp rather than marijuana. A plant needs about 1% THC or more to produce marijuana's mind-altering effects.

The large number of plants testing above the limit is part of a difficult research process for the nascent industry, said Shelley Choy, agriculture department hemp program coordinator.

"It's honestly expected and fairly routine in the sense that it is really hard to grow a plant that is 0.3% or below, and it is also really difficult in Hawaii because we have a really unique climate and photoperiod as compared to other states," Choy said.

Most of the business interest is in producing CBD products for the wellness industry. Hemp strains ideal for high CBD, a medicinal chemical that does not cause a high, tend to also have higher THC levels, Choy said.

The state approved various hemp seeds that can be cultivated in Hawaii and allowed licensed growers to request approval for other types of interstate seeds.

"Genetics which work in other states don't necessarily work the same here, and it is all experimental," Choy said.