Midwestern Hemp Database: Utilizing Grower-Cooperator Networks to Assess Variety Performance of Industrial Hemp Across the North Central Region

Results from this trial show most high cannabinoid hemp grown in the Midwest will begin to flower mid-August to early September, continuing reproductive growth until harvest in late September/early October. Importantly, significant variation in flowering windows are observed for some cultivars, while others flower more uniformly, suggesting varying degrees of genetic uniformity within seed lots.

Flowering date was significantly impacted by cultivar and environment/ hardiness zone but no interactions were significant. Across all cultivars, the mean 50% flowering date at the midpoint of hardiness zones 5b/6a was day 231 or August 19th. Cultivars were subsequently grouped into maturity groups based on mean expected flowering day: Following August 20th (Late Maturing) or Prior to August 20^th (Early Maturing).

Traditionally, photoperiodic flowering response due to geographic location has been discussed in terms of differences in latitude. For the purposes of this study, hardiness zones were used to reflect geographic location and correspond to the following approximate latitudes: Hardiness Zone 5a (~42- 45°),  Hardiness Zone 5b (~39- 42°), Hardiness Zone 6a (~38-39°), and Hardiness Zone 6b (~37-38°)

Across hardiness zones 5a (~37°) to 6b (~45°), average flowering date differed by ~7.9 days; this means that on average, cultivars experienced flowering initiation ~8 days later at the northern edge of hardiness zone 5a than they did in the southern edge of hardiness zone 6b. Growers may utilize this data to estimate approximate flowering dates based on their location relative to the average expected flowering dates observed. A similar delay in flowering date as hardiness zone decreases has also been observed when comparing the same cultivars evaluated in university station trials at Michigan, Wisconsin, and Illinois (see full report).

Agronomic performance ratings (germination, uniformity, overall performance etc.) are given as averages across all environments for each cultivar. These ratings were not analyzed for statistical significance given the subjective nature of the qualitative ratings and are meant to guide future research trials and cultivar selections only. In the same way, yield metrics across locations have historically been quite variable due to variance between and within cultivars and differences in grower-cooperator skill; for this reason, university station trials may be more useful/accurate sources of information for yield metrics and will not be discussed here.

Total THC and Total CBD were impacted by cultivar, sampling period, and location ( P < 0.05). Cannabinoid data is presented in terms of averages across all locations at each time point. THC and CBD generally increased from week three to week five, with cultivars exhibiting varying optimal harvest intervals for both compliance (THC) and profit potential (CBD) between weeks 5 and 7. This suggests that growers will want to consider both CBD and THC production when making harvest decisions.

The reality is many CBD dominant hemp cultivars currently on the market will go “hot” (Total THC >0.3%) if not monitored appropriately during flowering. To illustrate, 11 (65%) of the cultivars in the check program exceeded the regulatory limit at some point during the flowering period. Even with increased caution from farmers 29% of the 2,000 samples submitted into the MHD were above 0.3% Total THC regulatory limit across the 2020-2022 growing seasons.

Growers are encouraged to test their crop frequently during later stages of flowering to maximize production of cannabinoids while maintaining compliance. This data would suggest that the optimal sampling date for many cultivars will likely be 5 to 7 weeks (35 to 49 days) after flowering initiation to remain compliant. Data from the 2021 and 2022 growing seasons has been utilized to develop estimated compliant harvest schedules based on 95% confidence intervals.

CBD:THC is impacted by cultivar, sampling period, environment, and cultivar by environment interactions ( P< 0.05). CBD:THC of many of the hemp cultivars were unaffected by sample timing, remaining consistent throughout flowering. Similarly, CBD:THC of many of the hemp cultivars was unaffected by grower location, remaining consistent across environments. This supports previous work by researchers from Cornell University showing that CBD:THC remains stable throughout flowering for uniform cultivars.

Results show that most CBD dominant cultivars exhibit a linear (or curvilinear) relationship between Total CBD (%) and Total THC (%). Given this relationship, Total CBD (%) infrequently exceeds ~8% without exceeding the regulatory threshold of 0.3% Total THC. Considering that CBD:THC is mostly stable across flowering periods and environments, cultivars with a stable CBD:THC (>25:1) throughout flowering will help to maximize profitability while maintaining compliance. It should be noted that some cultivars are more impacted by environment or genotype* environment interactions; as such, heterogeneity across and within cultivars can make agronomic performance and cannabinoid development less predictable and difficult to evaluate. Due to the non-uniformity of the flowering process, unstable/non-uniform cultivars could reach maturity at different points in the growing season, which could have adverse impacts on testing and harvesting strategies at the field level. For this reason, growers may want to consider uniformity of growth and development of plants within a cultivar when making selections to avoid issues in the field for compliance and harvest.

For CBG Dominant cultivars, THC and CBG increased over time, with cultivars exhibiting varying optimal harvest intervals for both compliance (THC) and profit potential (CBG). None of the three CBG dominant cultivars exceeded the THC threshold for compliant hemp by the week 7 sampling period. CBG dominant cultivars may provide an alternative cropping option for those looking to reduce risk of noncompliance compared to production of CBD dominant cultivars

Growers will want to consider the following factors when making variety selections in their region:  Seed Quality (Germination, Uniformity, etc.),  Maturity Group (Photoperiod), Agronomic Performance (Yield and Quality), and Cannabinoid Development (Compliance Potential)

Growers will want to consider the hardiness zone and maturity group, as well as their potential interactions, when making variety selections. For example, growers in northern latitudes may want to plant earlier maturing cultivars to maximize the shorter growing season compared to their southern counterparts. In a similar fashion, growers may wish to grow cultivars of varying maturity groups to diversify and stagger field operations. Importantly, cultivars with a history of compliance may not be suited to a region while some cultivars with a history of high performance may not be reliably compliant. To better understand cultivar agronomic performance in a similar region, growers are encouraged to access local university cultivar trials for the most accurate regional information. Similarly, growers are encouraged to access the Midwestern Hemp Database and Cultivar Check Program Reports for the best information available regarding compliance potential of evaluated cultivars.