Hemp Fiber – Finding Value in the Supply Chain

Seasonal precipitation and temperature were recorded with a Davis Instrument Vantage Pro2 weather station, equipped with a WeatherLink data logger at Borderview Research Farm in Alburgh, VT (Table 4). June exhibited cloudy weather with standard rainfall. July’s rainfall saw a staggering departure from normal with 10.8 inches of precipitation, 6.74 inches more than the 30 year average. Much of Vermont experienced persistent rain in tandem with hazy conditions caused by Canadian wildfire smoke over the course of July and August. Despite the heavy rainfall, the well-saturated research farm did not experience the flooding that wrought havoc on many other farms in the state. Overall, from May to September there were 23.4 inches of rain and 2038 Growing Degree Days (GDDs) accumulated, which was 124 GDDs below normal.

Table 4. Seasonal weather data collected in Alburgh, VT, 2023.

Based on weather data from a Davis Instruments Vantage Pro2 with WeatherLink data logger. Alburgh precipitation data from August-October was provided by the NOAA data for Highgate, VT. Historical averages are for 30 years of NOAA data (1991-2020) from Burlington, VT.

Hemp Fiber Variety Evaluation Trial

Objective 1. Identify hemp varieties that maximize fiber yield. If successful, growers will be able to select varieties that help them reduce inputs and maximize yields.

Hypothesis: If growers select varieties best adapted to Vermont, then hemp fiber yield and quality will be maximized.

Table 5. The impact of variety on plant characteristics and harvest yield of industrial hemp fiber, Alburgh, VT, 2023. 

†Treatments marked with an asterisk (*) did not perform statistically different than the top performing treatment shown in bold (p=0.10).

‡LSD; least significant at the p=0.10 level.

^§NS; there was no statistical difference between treatments in a particular column (p=0.10).

Given the versatility of hemp in the market, one must be clear on their goals for end-use from the start. Whether it’s the choice of variety or seeding rate, agronomic practices will have an influence on the resulting crop. In our trial, our initial goal was to produce a dense stand of plants with stem diameters comparable to that of a pencil or chopstick (6-7mm). This is the recommended girth of plants grown for textile-quality bast fiber. Theoretically, stem diameter can be manipulated by the density at which the seed is sown. More seed will result in a greater number of thinner plants that stretch upwards to compete for sunlight in the canopy without much lateral branching. Others might optimize their growing conditions for high biomass yield, using less seed for the production of bigger, more spacious plants. Others still might prioritize hurd production, or dual cropping. Plants with a higher ratio of hurd fiber will have a thicker woody core. This is not optimal for textile production but is well suited for other industrial applications. Yuma hit the average target stem diameter with the second highest dry matter yield in the trial (Table 5). However, Yuma is not bred for textile grade fiber and did not yield a favorable ratio of bast fiber. Yuma is better suited for hurd production than for textile fiber.

 In our trial, Fiber 1 had the largest stem diameters with an average of 11.6mm, and the greatest dry matter yield of 12.1 tons ac^-1 (Table 5). Numerically, Fiber 1’s dry matter yields were nearly double those of many of the varieties but no statistical difference was detected between the fifteen varieties. This is likely the result of substantial variability across Fiber 1’s four replications, which causes a loss of confidence in the consistency with which it can produce such high yields. In other words, one replication yielded very low, one yielded very high, and the other two spanned the gap in between.

French varieties including Ferimon 12, Fibror 79, Futura 83, and Muka 76, continued to be consistent and reliable performers in our region (Table 5). These varieties also produced some of the highest bast fiber yields in the trial. Fibror 79 has a unique genetic marker that colors the stem and foliage yellow, as seen on the cover page of this report. This is a characteristic that is unique to some fiber hemp varieties and is linked to a more tender and less hearty stalk than some. For these reasons, Fibror 79 experienced severe lodging due to rain compared to its more robust counterparts.

The tallest of the fifteen varieties in the 2023 fiber variety trial was Fiber 1 by Kanda Hemp with an average height of 302cm (Table 5), or 9.9 ft. No other varieties produced average heights of statistical similarity, with the second tallest variety, Carmenecta, averaging 233cm. Fiber 1 also yielded the largest quantity of biomass, which was measured to be 12.1 tons per acre. Noting that Fiber 1 had a lower stand count than most at only 12.5 plants ft^-2, it is evident that this high yield was the result of the towering stature of the plants and not the density of the stand. No matter what the primary end-use is for an industrial hemp fiber crop, bast and hurd fibers are each a profitable byproduct of the other and turning the highest profit hinges on maximizing yields of both. Important factors to account for during the growing season include genetics, soil fertility, germination rate, seeding rate, and harvest timing.

Hemp Fiber Harvest Timing Trial

Table 6. The impact of harvest timing on plant characteristics and harvest yield of fiber hemp, Alburgh, VT 2023.

†Treatments marked with an asterisk (*) did not perform statistically different than the top performing treatment shown in bold (p=0.10).

‡LSD; least significant at the p=0.10 level.

§NS; There was no statistical difference between treatments in a particular column (p=0.10).

The trial results by fiber hemp harvest date are summarized in table 6. Our goal with this experiment was to observe the impact of harvest timing on plant characteristics and yield. The trial showed no statistically significant difference in plant heights or yield across the three harvest timings (Table 6). However, harvest date did appear to have an impact on stem diameter, with the thickest stems, averaging 8.2 mm, coming from HD4 on 28-Aug. Perhaps the most noteworthy data collected in this trial is that of bast to hurd ratio. The first harvest timing, which occurred 74 days from planting, yielded the highest percentage of bast fiber at 38.6% of the stalk. Neither of the following harvest dates yielded a statistically similar result. This data is aligned with the widespread belief that bast fiber quality and quantity can be expected to diminish with the onset of flowers and seeds. Given that the highest bast fiber percentage was observed in HD1 and the thickest stems were observed in HD4, it is likely that the hemp stalks are getting woodier as the plants transition from the vegetative stage to flowering. During HD1 we also saw the highest populations of plants at 1,011,714 plants ac^-1, with HD2 yielding a statistically similar result of 833,652 plants ac^-1. It is possible that the reduced population of plants in HD4 was the result of “self-thinning” or a die-off of smaller plants under the canopy by the time of harvest.

Hemp Fiber Retting Duration Trial

Objective 3. To evaluate the effect of different field retting durations on the properties of hemp fiber in Vermont’s climate.

Hypothesis: If growers become effective in identifying proper retting duration fiber quality will be optimal for the available markets.

Figure 1 shows the impact of retting time on the concentration of neutral detergent (NDF) and acid detergent fiber (ADF) over a five week period. The concentrations of both components increases until the 3rd week of retting at which point the concentrations begin to decline. The NDF consists of hemicellulose, cellulose, and lignin whereas the ADF consists of cellulose and lignin. At harvest the NDF and ADF concentrations were lowest as the material rets in the field there is a loss of easily degradable plant materials such as various sugars and pectins. The level of soluble carbohydrates was highest at harvest and declined by 76% from harvest until week 2 (Table 7). As the carbohydrates are lost during the "rotting" process the concentrations of less degradable material, the fiber, increase in concentration. The concentration of NDF and ADF reach a maximum at week 3 and this would indicate that much of the easily degradable material has been lost. At this point the NDF and ADF concentrations begin to decline which is likely a result of the degradation of the hemicellulose and cellulose after week 3. This preliminary indicates that hemp fiber was likely retted to an optimum point for textile production after 3 weeks of retting in the field. Additional work needs to be done to characterize the fiber and suitability for a variety of end-use products. 

Table 7. Impact of retting duration on plant fiber, lignin, and carbohydrates.

Hemp Fiber for Green Design – Finding Perspective and Partnership

The UVM Extension in partnership with Zion Growers, Hemp Hollow Processing, Vermont Green Building Network, Smokey House Farm, and the Northeast Climate Hub held a design brainstorming session to develop ideas for climate smart green building and design products using hemp bast and hurd fibers and other local fiber from crops grown in Vermont.  The session was called “Hemp Fiber for Green Design” held in August of 2023 at Vermont Marble Works in Proctor, Vermont.

Hemp can provide dual crops of grain and fiber, with multiple end uses, which are potentially carbon negative and renewable. Hemp concrete (aka hempcrete) offers a carbon smart alternative because of its low carbon impact, thermal properties and moisture buffering capacity with a low life cycle impact compared to similar products. The overall emissions balance is favorable due to biogenic CO₂ uptake during hemp growth and to CO₂ uptake by carbonation meaning that hempcrete blocks can have a negative carbon footprint and can act as effective carbon sinks (Arrigoni et al, 2017).

Hemp also improves diversification to Vermont's agricultural economy and provides value-added production opportunities, including new products for the bio-based green building sector which mitigates climate change and provides a healthy living environment.

During the UVM Extension workshop, 24 participants identified a number of barriers and opportunities to developing this emerging marketplace.  Zion Growers led a tour of the facility which showed what needed to be done to retrofit a large mixed-use space formerly used for marble cutting and manufacturing  to other uses including hemp drying, storage, processing, and design.

In addition to industrial hemp, the group also discussed other renewable fibrous materials which can be cultivated and sourced from Vermont and adjacent states. The sources are well-managed woodlands and farms harvesting timber, sheep wool, hemp, flax, and straw. These fibrous materials are noted for superior thermal, hygroscopic properties, and antimicrobial properties, as well as the fact they are renewable and have relatively short rotations.   In the session, participants considered green to be “climate smart,” that is, having a lower carbon footprint and emitting less greenhouse gases over the lifetime of the product than its conventional default choice.

Hemp and other natural fibers have been designed into insulation products, SIPs (structural insulated panels) and floor and wall coverings.   Young companies such as Hemp Hollow and New Frameworks Cooperative have found a growing niche in Vermont design using regionally sourced fibrous materials.  At the workshop, Alex Esher, Hemp Hollow, demonstrated the process of making hempcrete bricks. Esher is working on ASTM building standards for hemp.  There are also international standards for third party certification and systems to document and verify a product’s carbon credentials. However, most of these are geared to large companies.Compared to other part of the world, the USA is playing catch up with a hemp fiber industry in its infancy and in some ways is “bringing a historical crop back into the future, ” Esher says.  New businesses like his only became possible when the 2018 Farm Bill Act removed industrial hemp from inclusion in the Controlled Substances Act.

All in all, workshop participants agreed that more applied research and market development is needed to move this nascent industry forward both on the supply side to help farmers identify and grow the best varieties for fiber and also on the demand side in product development and raising customer awareness.  There’s more work to be done. Read more about hemp projects including research and educational activities on the industrial hemp page of UVM Extension’s Northwest Crops & Soils hemp programs.

 Alex Esher demonstrating hempcrete making, Proctor, VT

 Travis Samuels discussing hemp fiber storage in Proctor, VT