Keys to Success for Germination of Triploid Watermelon Seeds

By Bob Maloney, Novartis

Good germination depends on control of moisture, temperature and seed placement.

At Johnson Melon Corp. (JMC), "Sunshine Lg-3" is used as a planting medium, but any good commercial brand normally used for transplants will work.

• Pre-moistening the Planting Medium:
  The medium should be pre-moistened to obtain the correct moisture level. The reason for this is that any free moisture will be taken up by a triploid seed, and the seed will 'drown'. At JMC, the top of a 35-pound plastic-enclosed bale of medium is opened, and the bale is placed on a scale set at 50 pounds. Water is added until the scale balances at 50 pounds.

  The moistened medium is left to drain overnight. This allows any excess moisture to drain off and also ensures that the medium has absorbed the moisture. This is especially important when coarse medium is used.

  It is generally considered that triploid seeds germinate poorly at temperatures below 70 degrees F. (21 degrees C.). Seeding at JMC is done in March, and nights are cold. To avoid having very cold medium, the moistened bales are placed in a large heated cabinet during the night. A bathroom heater in the cabinet brings the temperature of the medium to 85 to 90 degrees F. (30 to 32 degrees C.).

  When the medium is ready to be used, the bale is emptied, and the medium is stirred to ensure even moisture. The moisture level is checked by tightly squeezing a handful of the medium. If water drips from the fist, the medium is too moist. There may be some wetness on the hand. If the medium is too moist or too dry, more medium or water should be added to adjust the moisture to the correct level. This is the most critical step in germinating triploid seed.

• Planting Depth:
  The seed should be planted at a depth of .75 to 1.0 inches deep in the cell. This allows the seed to turn as it germinates without pushing out of the medium. It also allows good maintenance of the moisture level while the seeds are germinating. At JMC, 98-cell trays are used for planting. Trays with 128 cells work well also, and growers have had success with trays with greater numbers of cells. Trays with less than 1.5 inches of depth may restrict root growth if the seed is placed at .75 to 1.0 inches deep.

  A practice not used at JMC, but with which others have had good results, is to place one or two wheat seeds in each cell with the triploid seed. This increases the root mass, and makes the seedling easier to pull. The sprouted wheat can be nipped off when the transplant is pulled.

  After seeding, cover the trays with pre-moistened planting medium. Many commercial transplant growers have success covering the trays with Vermiculite. This requires experience for correct moisture control. Perlite is not recommended.

• Germination Room:
  A germination room can be any enclosed space in which heat and humidity can be controlled. At JMC, the germination rooms are former egg incubation chambers. Bathroom heaters on a thermostat control the temperature, and pans of water on the floor provide humidity.

  The seeded trays are placed in the germination room for 48 to 72 hours, and should be removed when the first seedlings emerge. During this time, the temperature should be maintained at 85 to 90 degrees F. (30 to 32 degrees C.), and the relative humidity between 90 and 100 percent.

• Greenhouse Management:
  Once the seedlings have begun to emerge, move the trays to the greenhouse. Maintain a temperature of approximately 80 to 85 degrees F. (27 to 30 degrees C.) until germination is complete.

  During the first week or ten days, water only enough to keep the planting medium moist. The medium on the top of the tray is only very lightly watered, the moisture at the level of the seed will remain correct. Over-watering prior to complete germination will destroy ungerminated seeds.

  When the seedlings are established, normal watermelon transplant production practices will achieve sturdy plants.