Improve your propagation facilities

A key to high-quality seedlings and rooted cuttings is a well-designed propagation facility. For seedling production, starting seeds in a germination/growth room can reduce production time by 15 to 20 percent. For cuttings, adding a fog system to the propagation area can give plants a better start.

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Temperature, humidity, air movement and light are the major environmental factors to consider.

Germination chamber particulars

Some growers install a germination (sweat) room for seed germination. The room needs to be large enough to hold all the flats that are to be germinated at one time with some room for expansion. The location can be in a basement, head house or garage. The walls of the room should be insulated and contain a vapor barrier on the room side of the insulation. A mist or fog system keeps the relative humidity at near 100 percent.

Root-zone heat or fin radiation can be installed to provide heat. Install enough heat to maintain a temperature of 85°F. Control the heat with a thermostat that has an accuracy of +/-1°F. A small circulating fan can help keep the temperature uniform although some growers use the variation to germinate seeds with different temperature requirements. Provide a floor drain for water removal.

Some seeds benefit from supplemental light at 10 to 100 footcandles, so fluorescent light fixtures may be necessary. Dividing larger rooms into sections with plastic curtains allows slightly different environments to be maintained.

Seedling flats can be placed on racks or handled on carts.

Timing is the most critical factor in using a germination chamber. Seedlings have to be removed at the right time or they begin to stretch. Some seeds germinate overnight if given the right conditions.

Separate growth rooms

Although germination can be done in a growth room, it is better to have separate rooms for germination and initial seedling growth. The problem arises in that until the seed radicle emerges, the moisture content of the germination substrate should be kept near 100 percent and very little light is needed. After radicle emergence, the moisture content should be reduced to 40 to 70 percent and light levels increased to prevent stretching. Unless the growth room is divided, only one moisture level can be maintained.

Lighting in a growth room is usually provided at levels of 400 to 2,000 footcandles. This can come from fluorescent or high-intensity-discharge lamps. High-output fluorescent lamps can give the high level needed without taking up too much room.

Providing adequate heat

Almost any greenhouse can be used for germination, although the greater height of a gutter-connected greenhouse aids in air temperature buffering and the addition of energy or shade curtains gives better light and temperature control.

If germination is done on the floor, root-zone heat is desirable. This heating system provides the temperature range (65°F to 85°F) needed by the root zone.

If germination is done on benches, then on-bench or under-bench heat is necessary. In addition to the root-zone heat, additional heat is needed in the greenhouse to keep the air temperature at the desired level. Root-zone heating systems provide only about 25 percent of the total heat needed on the coldest nights. For germination areas up to 3,000 square feet, a domestic hot water heater can provide the heat necessary for the root zone. For larger areas, use a boiler.

Temperature control

Accurate temperature control is important. The best choice is an electronic thermostat with a remote-bulb sensor placed in a representative germination flat. This method can maintain the temperature within 1°F of the desired setting.

Cooling is also necessary. A shade system can reduce light levels on new seedlings and help hold the temperature down. A fan and shutter system with thermostatic control will do a good job.

For winter/spring propagation, about 2 cubic feet per minute of fan capacity per square foot of floor area is adequate. The air intake should be baffled to direct the incoming cool air toward the ceiling or brought in through a perforated poly tube to avoid cooling the flats.

Air circulation is necessary to maintain uniform temperature. A horizontal-airflow system works well to mix air. This system can also be used to provide dehumidification by removing moisture from the surface of the flats.

After the seedling radicle emerges, the germination medium is usually dried out via evapotranspiration to the germination 2 level of 40 to 70 percent range. This lower humidity induces faster flowering in many plants by one to two weeks.

Lighting is easier to install in a greenhouse. High-intensity-discharge light fixtures equipped with sodium or metal halide bulbs are suspended from the frame or trusses. The best light level will depend on the cultivars grown. A level from 350 to 2,000 footcandles should be available. Light fixtures can be located so that some can be unplugged to lower the light level.

Humidity vs. transpiration balance

To achieve good propagation, a balance between humidity and transpiration is needed to allow water and nutrient uptake without excess dehydration. For cutting propagation with a dense foliage canopy and little air movement, a boundary layer of moisture approaching saturation develops around the cuttings. If the rooting medium is also saturated, there is a potential for problems from fungi, moss, botrytis and fungus gnats.

On the other hand, when the air temperature is high and the leaf temperature increases, water loss can exceed the ability of the plant to take up moisture. This can lead to stress in plant cuttings. Fog or mist at this time can reduce the air temperature and increase humidity in the plant canopy. Fog is a better choice since it doesn’t apply excess water that can saturate the medium.

Fog systems produce droplets that are less than 50 microns. Typical systems use piston pumps that develop a pressure in the 1,000 to 1,500 pounds per square inch range and deliver fog through stainless steel or ceramic nozzles.

Mist droplet size is in the 50 to 100 micron range. Mist can be applied with overhead nozzles or with a boom system. Typically mist nozzles have an output of 0.1 to 0.3 gallons per hour.

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- John W. Bartok