Trialing new hemp genetics By Javier Garces

Treadwell Farms’ extensive program for testing different hemp cultivars has led to some important observations for growing the crop.

Choosing the right genetics is one of the most critical decisions growers face. At Treadwell Farms, we have grown over 40 hemp cultivars beginning with the Florida Agricultural Mechanical University (FAMU) Hemp pilot project in 2020. Florida has a very unique growing environment compared to other states, and we feel it is very important to run trials prior to offering specific genetics to our customers. We have also grown these various genetics throughout the last several years using different growing methods including in-ground outdoor production (raised beds with plastic mulch and drip tape), as well as containerized production in greenhouses, shadehouses and outdoors on ground cloth. We have been very fortunate to work with a diverse group of farmers spread throughout the state growing in these various methods.

Irrigation and fertilization

Genetically speaking, even though the various cultivars come from the same species, we have observed wide differences in irrigation and fertilization requirements, as well as in susceptibility or tolerance to insect pests and diseases. As for fertilization requirements, at Treadwell Farms we allow the crop to somewhat dictate the fertilization regime. When growing in containers, we take both pour-through leachate readings and send off tissue samples to a lab for analysis. There are several labs, both staterun and private, that will analyze for plant nutrient levels, soil/media samples, and disease analysis. The pour-through technique is a way growers are able to check the pH and EC or ppm (two different units to measure the same thing) of container crops on site. The pH refers to how acidic or basic a soil is, while the EC/ppm provides a measure of the overall soluble salt concentration of the soil. These are both indicators of the amount and availability of nutrients for the plant.

This technique is performed as follows: 30 minutes to two hours after irrigation, ½ cup (120 mL; 4 fl. oz.) of distilled water is poured over the surface of a 1 gallon container or 1 ½ cups over a 3 gallon container for pine bark/sand potting mixes. If the media contains peat moss or other organic substrate amendments, additional water may be required. The leachate can then be captured when it runs out of the bottom of the container to measure pH and EC/ ppm. Use the appropriate meter to collect data, be sure that the instrument is calibrated (weekly or as needed). This information should be recorded on a data collection sheet and provides the grower the nutritional status of the media in those containers.

Image 1. Botrytis bud rot. Photo: Javier Garces.

Plant tissue samples are collected at various points throughout the growing season and sent off to a lab for nutritional analysis. This gives the grower information if there is any nutritional imbalance during the different growth phases of the crop’s life cycle. This allows us to correct any issues prior to the plants exhibiting deficiency symptoms, and can also confirm the issue if symptoms are already being observed. Growing different cultivars, we have observed that certain genetics will take more fertilizer compared to other cultivars, even though they were planted at the same date, same age and same size. For example, some cultivars were able to take high levels of fertilizer (over 2,000 ppm) while others appeared to max out at lower levels (approximately 1,500 ppm or less).

Insects and pests

Another observation in growing different genetics in side by side trials has been in susceptibility or tolerance to insect pests and diseases. A clear example was in a field trial with what we will call Cultivar A and Cultivar B. The farmer had many years of experience growing a wide variety of crops. This hemp crop was grown in the field, using raised beds with plastic mulch and drip tape. The two diseases observed in the field were Botrytis bud rot (Botrytis) and Southern blight (Sclerotium rolfsii). Botrytis is a very common, widely distributed disease on a wide variety of crops grown in the field, in greenhouses, during the drying/curing phase and in storage. This pathogen leads to fruit/stem rots, with a white/gray or light brown moldy growth. The disease develops as it overwinters in the soil as mycelium, in plant debris or as sclerotia (hardened survival structure). It requires cool, damp weather for best germination.

Image 2. Southern blight, with white mycelium growing at the base with mustard seed-size sclerotia. Photo: University of Florida plant pathology department.
Image 3. Southern blight, with the diseased plant at the end of the row desiccated. Photo: Javier Garces.

Disease can be expected when nighttime temperatures fall below 60° F with relative humidity at 90% or higher. Southern blight can be a destructive disease to numerous vegetables and fruit crops, especially in tomato, pepper, melon, and watermelon. Plants are attacked just below the soil and end up girdled. This results in infected plants wilting then desiccating completely in a brief time period. The pathogen grows mycelium over infected tissue and the soil surface, resulting in a white mat with tan/brown, mustard-seed-size sclerotia. Environmental conditions that are favorable for Southern blight disease development are high temperatures (80 to 95° F), humid conditions and an acidic soil. Sclerotia germinate at pH 3 to 7, but is inhibited at pH levels above 7. These two pathogens were confirmed with a lab analysis after their discovery during routine scouting for pests and diseases.

Both cultivars were planted on the same date and roughly the same size. They were fertilized based on soil and tissue analysis. Cultivar A was stockier, with denser flower and appeared more susceptible to Botrytis (Image 1). There was very little to no Southern blight observed in Cultivar A. Cultivar B had very little Botrytis observed but much more Southern blight (Images 2 and 3). There was a clear distinction here, side by side, where A was more susceptible to Botrytis but appeared to be less susceptible to Southern blight, whereas B was the opposite (less susceptible to Botrytis but more susceptible to Southern blight). This susceptibility or tolerance to the two diseases can be attributed to the difference in genetics, as all the other variables such as planting date, size/age at planting, irrigation schedule, fertilizer regime, exposure to environmental conditions and IPM program were the same.

Need for trialing

In conclusion, having some sort of on-site trials is important as farmers and growers learn to grow this new crop. One of the main pieces of advice we give to new farmers (or even experienced farmers growing this crop for the first time) is to start small. When new or potential farmers ask how many different cultivars they should grow, my answer is usually a question along the lines of “How many are you willing to keep track of?”

Additional questions I ask are: “How much time are you willing to spend observing, collecting data, to help you decide the genetics that work best for your area?” and “What are your end goals; in other words what is the end product you are growing for?” These are just a few of the questions farmers should ask themselves prior to planting. Each situation is unique, in both environmental conditions and in end goals.

Also, certain genetics may perform great during a specific time of year in your area and struggle at other times of the year. The only way for farmers to really decide what works best for them begins by asking these types of questions, then making the decision to plant at least a couple of cultivars and make observations throughout the growing season. There are many factors critical to a successful crop, and choosing the right genetics is high on that list.

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Javier Garces

Javier Garces, Ph.D., or “Dr. G,” is a professor and the program chair for the plant science and agriculture technology program at Valencia College and horticulture advisor for Treadwell Farms ( He can be reached at

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