Tray filling is a critical part of production. Packing the media too tightly may result in plant roots not penetrating the media (spiral roots), while packing too loosely may result in cells which do not wick properly (dry cells). One of the several brands of media intended for tobacco transplant production should be used. Most batches of media require water to be added for proper packing. The amount of water needed varies greatly. It is best to practice wetting a bag or two of the media and filling a few trays a week or two before you plan to seed. Float the trays and observe if any dry cells are present. Adjust the water or packing as needed. A filler box greatly improves packing uniformity as compared to hand filling. The media needs to be checked for clods and sticks that may interfere with filling. Sticks can also lodge in cells, causing dry cells.
Greenhouses in South Carolina should not be seeded before February 1. Traditionally, greenhouses have been seeded earlier. It is now known that good plants can be produced in less time than originally thought. Delaying seeding will also result in energy savings, and should reduce the number of clippings needed. The February 1 seeding date will provide good transplants in late March to early April.
Proper seeding is the first step toward obtaining maximum seedling usability. Either tube or vacuum seeders can be used. Both types need frequent checking to be sure they are delivering one seed per cell. Use only fresh, high quality seed intended for direct seed greenhouse use. Seed intended for precision seeding field beds or custom-coated bare seed may not be suitable for use in the greenhouse. Often these seeds are of lower germination and vigor than greenhouse seed. While this poses no problem in field beds, it can result in lowered usability in the greenhouse. Do not use primed seed saved from years before. Priming damages the long-term storage ability of tobacco seed. Low germination and seedling vigor can result from using old primed seed.
Care must be taken as the trays are floated to avoid rough handling, which may dislodge seeds, resulting in double and missing plants. There is no need to water over the top in the float system. A properly packed tray will provide sufficient moisture for germination. For proper germination, the greenhouse floor temperature should be held at 68 to 70 degrees F until germination is complete. Recent records indicate 68 degrees F at night and 86 degrees F in the day as ideal for germination of most varieties. Thermometers should be located on the floor, not at eye level. There can be a great difference between the floor temperature and the temperature at 5 feet (see engineering section for details of temperature control systems). After germination, the temperature can be reduced to 50 degrees. If cold injury symptoms appear (it looks the same as in the plantbed), increase temperature slightly and/or readjust the horizontal air flow fans to prevent cold spots. Usually, cold injury causes no permanent damage. Some varieties are more sensitive to cold injury and may require slightly higher night temperatures.