A three-year study has found that trimming the tops of industrial hemp plants can reduce their height by approximately 14% without significantly affecting seed production, potentially making the crop easier to harvest with conventional agricultural machinery.
The study, published October 6 in the journal Agronomy, was conducted by researchers from Italy’s Council for Agricultural Research and Economics. Scientists examined three hemp cultivars grown under outdoor field conditions in northern Italy between 2023 and 2025.
Researchers tested a cultivation technique known as apical topping, which involves cutting off the upper portion of a plant’s main stem to alter its growth. During the experiment, approximately 20 to 30 centimeters were removed from the tops of selected plants during their vegetative stage.
At harvest, topped plants averaged 179.5 centimeters in height, compared with 208.9 centimeters for plants left untrimmed. The difference represented a statistically significant 14% reduction.
Despite their shorter stature, the topped plants maintained comparable seed production. Average yields reached 302 kilograms per hectare for topped plants and 325 kilograms for untreated plants, a difference researchers determined was not statistically significant.
Topping also did not significantly affect seed quality indicators, including thousand-seed weight and the proportion of impurities found in harvested material.
The experiment involved three hemp cultivars: Codimono, Carmaleonte and Futura 75. Researchers found that growing conditions and cultivar selection had considerably greater effects on overall productivity than topping.
Weather conditions were particularly influential. Average seed yields increased from approximately 170 kilograms per hectare in 2023 to nearly 565 kilograms in 2025, reflecting differences in water availability and seasonal growing conditions.
The researchers said shorter plants could be particularly advantageous for commercial hemp operations, where tall stems and substantial plant material can complicate mechanical harvesting.
Reducing plant height to approximately 1.8 meters could decrease resistance during harvesting and potentially reduce machinery clogging, making conventional equipment more practical for industrial hemp cultivation.
Because the experimental plots were harvested manually, those mechanical advantages remain to be tested directly.
The findings nevertheless suggest that hemp producers may be able to modify plant structure to improve harvesting conditions without sacrificing seed productivity, providing another potential tool for commercial hemp cultivation.
