Gilbert Miller, Clemson Extension vegetable specialist, with the germination box.

DATE: 5/30/2005

CONTACT: Gilbert Miller, (803) 284-3343, ext. 225

WRITER: Tom Lollis, (803) 284-3343, ext. 241

Germination room for seedless melons need not be expensive

BLACKVILLE – Watermelon lovers are more and more demanding that their melons be seedless.

“The market is about 80 percent seedless right now,” said Gilbert Miller, Clemson Extension vegetable specialist at Edisto Research and Education Center . “The Southeast is the only section of the country that still grows seeded melons for the market. Even so, about 70 percent of the melons produced in South Carolina are seedless.”

Seedless melons must be planted from transplants, since warm conditions for germination are critical. Some producers grow their own transplants, but others order from greenhouse operations.

For producers wanting to start growing transplants, commercial germination rooms with precise controls for temperature and humidity can be expensive. However, for less than $60 a producer can follow Miller’s lead and make a germination box to produce enough transplants for three to five acres of melons.

“Last year I just taped together some one-inch thick sheets of foam insulation to make a box 4 feet wide, 4 feet deep and 5 feet tall,” he said.

Miller then placed metal racks into the box to hold seed trays. On the bottom he placed a simple heater, the most expensive part of the project at $27.

Right above the heater he placed another sheet of insulation to keep all the heat from concentrating in one spot and to protect it from dripping condensation. The heater requires trial and error to find the right settings to maintain a range between 87 and 92 degrees F, so he stuck two maximum/minimum thermometers in one side, one high and one low, to  monitor the temperature.

High humidity is also needed for germination of diploid, or seedless, watermelons. The seed coat is thicker than the coat on seed of seeded melons. Diploid seed also contain a larger air pocket inside the shell, which can absorb excessive amounts of water and lead to rotting.

To avoid the problem, Miller advises filling the seed trays first, then letting them drain thoroughly after watering before adding seeds. Put the trays in the germination box. Don’t add any more water until after they germinate. To maintain high humidity, he soaks a burlap bag and puts it on the floor of the box.

“Leave the seed trays in the germination chamber for no more than 48 hours,” said Miller. “If you leave them in too long, the seedlings begin to stretch and you’ll wind up with leggy plants, which are vulnerable to wind damage in the field.”

Miller gets between 85 and 95 percent germination with his cheap box.

After germination the transplant trays are kept in a greenhouse at around 75 degrees until time to plant, which is about 28 days from the time the seedlings are started.

Timing is the drawback to having someone else produce your own seedlings.

“When you tell the greenhouse your planting date, those seedlings will show up on that date whether you are ready to plant or not,” said Miller. “If you’ve had a week of wet weather, the seedlings will have to sit in boxes for days waiting for the field to dry out, and they won’t be in such good shape. If you grow your own transplants and have greenhouse space in which to hold

them, they will be in better condition than if they had to sit in shipping boxes.”

Watermelons are grown on around 11,000 acres in South Carolina , with an annual value of more than $7.5 million. While watermelons are grown in every county in the state, the major commercial production is concentrated in the counties of Allendale, Bamberg , Barnwell, Colleton, Hampton and Chesterfield .

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