Solid seedlings

Germination cart

For small growers, one or more carts can provide adequate propagation space. A 24-inch wide by 48-inch long by 72-inch high cart can have 12 shelves spaced 5 inches apart and hold 48 11- by 22-inch plug trays. With casters, the cart is mobile and requires only eight square feet of space. Commercial carts are available, or you can fabricate your own using a plant shipping cart with added shelves.

For germination, temperature is the most important factor. Each species has optimum requirements. For most seeds the ideal temperature is 70° F-75° F. If located in a warm room, no additional heat is needed. If heat is needed, a thermostatically- controlled electric heat mat or small aquarium heater at the bottom will satisfy the needs. If more moisture is needed, a heated water pan at the bottom can provide this. To be more efficient and retain more light, the cart should be enclosed with plastic or board insulation.

Germination (sweat) room

For the larger grower needing more space, a germination room can be installed in the headhouse, basement, garage or separate building. The corner of an existing building adjacent to an outside wall is ideal. Walls can be constructed of 2 x 4 lumber with a polyethylene vapor barrier on the room side. Add an inch or two of polystyrene or polyurethane board insulation if the building is unheated. Finish the wall and ceiling surfaces with poly board or waterproof plywood painted with a white-polyester or epoxy paint to give an easy to clean surface.

Plug trays can be placed on fixed or portable racks. Use metal or pressure treated wood. Allow for access from one side (24-inch width) or both sides (48-inch width). A 24-inch wide aisle will allow easy movement of plants. Racks should be built to fit the tray size without wasted space. Some growers have used 2-foot x 4-foot rolling racks that allow loading and unloading to take place outside the room where more space is available.

Depending on the design, location and use of the room, heat may be needed. For example, a 10-foot by 12-foot insulated room in a headhouse may require less than 500 Btus of additional heat to maintain 75° F when the temperature in the headhouse is 55° F. Heat can be supplied by a portable electric or a gas unit heater. A mini-split heater — air conditioning unit would supply both heating and cooling withs some energy savings.

Additional moisture may be needed and can be supplied by a portable humidifier. To provide uniform temperature and moisture, air circulation may be needed. One or two small circulating fans located above the plant canopy can provide this. It should be set up to give a circular air flow that mixes the air top to bottom. A total fan capacity of two cfm/sq ft of floor area should be adequate.

Growth room

To gain an additional two to three weeks of use, the carts or room can be fitted with supplemental lighting. Shelves need to be spaced a minimum of 8 inches apart so that the light will not burn the young foliage. Energy efficient, LED strip fixtures can be attached to the undersides of the shelves or mounted vertical to adjacent walls. A level of 100 to 250 µmol/sq m-sec is usually adequate for young seedlings. Daylength should be enough to get the desired daily light integral (DLI). Lighting at this stage will increase growth and root development resulting in stronger plants that flower earlier.

The heat from the lamps can be used to provide room heat if needed. Too much heat is more of a problem. Large banks of lamps can easily overheat the room. Ventilation with outside air is usually the best solution. A small exhaust fan installed in one endwall and a couple of motorized intake shutters or a perforated plastic tube for makeup air. A thermostat can control the operation of these. Air conditioning is generally too expensive. Another option is to utilize the extra heat in an adjacent greenhouse or work area. A small thermostatically controlled fan or blower through a wall usually works well.

The shorter sprouting time and greater uniformity usually justifies the expense of installing a germination chamber. It can save energy by delaying the start of your greenhouse.