Growing inoculated plants at the Tri-Histil Greenhouse, Mills River, NC

Photo by Tom Baszler A grafted watermelon transplant is ready to ship.

Penn State Extension horticulture educators and specialists bring deep knowledge and experience to the job. But like any field of labor, there are developments in horticultural science, marketing and trends. Staying active requires lifelong learning through courses, conferences, and reading scientific and trade journals.

Another way to stay current is to participate in professional development horticulture tours. This type of activity allows participants to step out of their familiar surroundings and see gardening from different perspectives and interact with a wider range of gardeners and garden lovers.

The Penn State Extension Educators Planning Committee created a horticultural tour in western North Carolina. The area is rich in jewellery, fruit and vegetable products. 21 teachers and specialists participated in the last week of June 2022. The following series of articles will provide an overview of our professional development tour.

One stop on our tour was to the Tri-Histil Greenhouse, an operation that takes nearly 90,000 plants daily through the transplanting process for vegetable farmers up and down the eastern US to be incubated by Bert Lemcus, the general manager.

Planted plants cost more than plants that grow on their own. In fact, Bert stated that unpainted plants can cost 3 to 3.5 times more. For many farmers, this increase in value is important, because transplanted plants provide an alternative to the fumigation used to prevent diseases caused by soil-borne pathogens. Using grafted plants is a way to reduce plant stress caused by cold, heat, salinity, and more. Researchers have also shown that fruit quality improves depending on the situation. We saw this in our study when evaluating muskmelon (cantaloupe) cultivars. We got the fruit when they were combined “Aphrodite” scion and “RS841” The rootstock may have a better taste “Aphrodite” Alone.

Photo by Elsa Sanchez Scions and rootstock seedlings are grown in different parts of the greenhouse.

In addition to muskmelons, American farmers are increasingly growing sliced ​​tomatoes, eggplants, peppers, cucumbers, and melons. Ninety percent of the cuttings produced by Tri-Hishtil are watermelons. Of these, 75 percent are triploid, or seedless, and 25 percent are diploid, or seedless.

Watermelon seedlings are mainly used for resistance to the fungus Fusarium oxysporum f. sp. niveum which causes fusarium wilt. This fungus is host-specific, which means that it is only a problem in water and does not affect other plants. Infected plants first stop and wither in the heat of the day. This frustration subsides by evening. Over time, plants will completely collapse and die. Fusarium oxysporum f. sp. niveum is soil-borne and can remain in the soil for up to 10 years, making it very difficult to manage.

A unique hybrid of squash and melon cultivar Carolina Strongback from F. They have some resistance to Oxysporum F. sp. niveum and therefore to fusarium wilt. interspecific squash hybrid has high resistance; However, it is susceptible to root knot nematodes. on the other hand,

“Carolina Strong Back.” It has moderate resistance to F. oxysporum f. sp. niveum but highly resistant to root knot nematodes. Farmers choose which species to produce based on the problems they face.

In addition, both root crops provide plants with more energy. In practice, the number of plants can be reduced by half or 2/3, which can offset the high cost of planting.

Photo by Elsa Sanchez Note the cotyledon on the root (white arrow) of this transplanted watermelon plant.

The challenge with using these root crops is the delay in first harvest. Stronger root crops require a different irrigation system and fertilizer schedule than other crops. Burt used a more powerful rootstock analogy compared to a standard engine or rootstock on unarmored plants. To overcome this challenge, Tri-Hishtil is working to adapt irrigation practices, fertilizer rates and plant needs. Burt also mentions delaying early fertilization with these root crops, which can be especially beneficial given current fertilizer prices.

Tri-Histil grows to order, and customers decide which scion and which rootstock best meets their needs. After this is decided, the process continues by preparing trays for sowing in the greenhouse. Consistency is critical. Trays, media, and other supplies are kept in an environment maintained at a temperature of 68∂F year-round.

Watermelon seeds cost about 25 cents each. For reference, common field tomato seeds cost 6-10 cents each. Because watermelon seeds are expensive, they must be handled with care. Planting 40% more seeds than required ensures that enough transplants are prepared for customers.

After planting the seeds, the team members apply warm water to the boxes to bring the temperature into a range suitable for germination. Also, after washing the water, weigh the tray. From this point on, adding more water depends on the weight of the dish that is on the table. Next, the trays go into the growing room.

After 9 days to calculate their maximum strength level, the rooting plants begin. A staggered planting between the rootstock and the scion will allow both sets of plants to reach a good stage for sowing at the same time.

Photo by Elsa Sanchez The chart on the tray tracks the weight of the flats to know when to water.

After the plants have germinated, the plants and rootstocks are placed in different parts of the greenhouse to have extra light throughout the year. When the seedlings reach a good stage, they move to the nursery.

Tri-Hishtil employs about 80 manual workers. Each printer takes a squint and root throughout the process. A reasonable planting rate is 160-170 plants per hour, and Burt says the planting success rate is between 93 and 94 percent.

Watermelon planting is challenging to automate because it requires precision, which is difficult to achieve with a machine. Grafters remove the covering of the plant, leaving one of the two cotyledons on the root. Each cotyledon has a bud at its base. Grafts leave a single cotyledon on the membrane but remove the bud. When planting tomatoes, seedlings remove both cotyledons from the root. This simplifies the process and opens the possibility of automation.

In addition, during transplanting, transplants remove the root from the interspecific squash hybrid or surface. “Carolina Strong Back.” Watermelon root has a higher strength compared to root. After a week of healing, the root system is rebuilt.

After planting, the plants are placed in a curing room with carefully controlled light, relative humidity and temperature and a photo period of 16 hours for 7-8 days. Plants are strong and sent after curing. The whole process takes about 6 weeks. You can see this process in a video on the Tri-Histil website (

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