University of California
Division of Agricultural Sciences
Successful rooting of cuttings or germination of seeds requires proper temperature, moisture supply and light intensity. Of these, moisture supply is usually the most difficult to control adequately. Water mist, or mist propagation, is a means of automatically maintaining moisture supply near optimum, on a small or large scale.
Mist propagation will not eliminate the necessity of properly taking the cutting or handling the seed, nor will it eliminate the need for careful disease control. However, it offers a means of automatically supplying moisture during the critical periods of propagation.
Select an outdoor location that provides filtered shade throughout the day. The location should not be windy–it may be necessary to erect some wind baffles around the propagation area. A convenient method of controlling both light intensity and wind would be to make a small plastic shelter. Wire is use to form the frame and hold the plastic. Cut holes at the top for ventilation. If shading is needed, cheesecloth may be placed on top of the plastic.
The medium for the germination of seeds or the rooting of cuttings should be porous, well aerated and well drained. Usually, peat moss mixed with an equal amount of fine sand, perlite or pumice is excellent for growing rooted cuttings or seedling. Sand or perlite may be used alone but is not as good as the above mixtures.
Temperatures of 65°F (18°C) to 75°F (24°C) should be maintained in the medium. Air temperatures of 50°F (10°C) to 69°F (15°C) are satisfactory. Higher air temperatures are not detrimental, but lower temperatures may cause injury. If the temperature of the water used for mist propagation is low, the temperature in the medium will be below optimum, and rooting or germination will be delayed or cease. To remedy this situation, use soil heating cables under the pots or flats.
Use light intensity equivalent to open or diffused shade. Mist propagation may be used out of doors under light shade, in greenhouses and indoors under fluorescent lights. Under lights indoors, use 40 watt, warm, white fluorescent tubes suspended 12 inches (30.5 cm) above the tops of the cuttings. Two tubes in a standard fixture would be sufficient for a space 3 feet (1 m) wide and as long as the tubes. The electrical system and the fluorescent tubes should be shielded from mist.
Adequate drainage of runoff waters necessary. Outdoors or in greenhouse, there should be a hard surfacing or gravel on the ground. Indoors, provisions must be made to catch the water and dispose of it.
Intermittent mist–water spray used only part of the time on a regular basis–has been superior to continuous mist. Not only is less water used, but the resulting plants are superior.
While there are many types of controlling devices for mist propagation, for the average situation, a clock-controlled setup is adequate. The parts and their functions are:
- Day-night timeclock to turn on the setup only during the daytime. Unless unusual drying conditions exist, misting during the night usually is not necessary.
- Interval cyclic timer to regulate the length and the frequency of the misting. Under average conditions, a 5 to 10 second misting period every 5 minutes should be sufficient. The duration and frequency of misting is regulated to maintain a film of water on the leaves of soft wood cuttings. Some experimentation and adjustment probably will be necessary to insure this under the condition of use.
- Magnetic water valve to turn on the water. Under usual conditions, use a normally open valve. In case of electric failure, this valve will open, thus maintaining the film of water on the cuttings.
- Mist nozzles come in many sizes and shapes. A baffle type generally is most satisfactory as it operates efficiently under low pressures. Oil or spray nozzles also may be used. Select nozzle suitable for the area to be covered and the placement of the pipe.
- Waterline strainer removes particles from the water that may clog the mist nozzles.
SMALL-SCALE PLANT PROPAGATION UNITS
The home gardener often wishes to propagate a few plants for demonstration, to increase a highly desirable shrub or to start plants early for the garden. Generally the systems used in nurseries are too large and require more care and attention than the average homeowner can give. However, many small-scale units may be made from inexpensive items commonly found around the home. These units are convenient to use, easy to care for, do not require constant attention and may be conveniently located in the kitchen, on a porch or outdoors in a shady location.
An aquarium makes an ideal unit for home plant propagation. Cover the bottom with a 1 inch (2.5 cm) layer of pea gravel for drainage. On top of this place 3 to 4 inches (7.5 to 10 cm) of a propagation medium such as sharp sand, vermiculite or pat moss mixed with sand or perlite. Or you may place small pots or plastic trays on the gravel layer. Moisten the medium, and the unit is ready for cuttings or seed. Cover the aquarium with glass or plastic to maintain high humidity in the aquarium, prevent the cuttings from wilting and hasten rooting.
Large plastic pots may be converted into excellent units. A 6 to 8 inch (15 to 20 cm) flowerpot is a convenient size. Seal the drainage holes with a material such as putty and fill the pot with the medium. In the center of each pot place a 2 inch (5 cm) clay pot with the drainage hole filled as above. Moisten the medium and insert your cuttings. Fill the small pot with water.
Water passes slowly through the porous sides of the clay pot into the medium, keeping it uniformly moist. At the same time evaporation from the surface maintains moisture in the atmosphere. If all the water is used before rooting occurs, fill the pot again.
Place a plastic bag over the cuttings and tie the open end against the pot. Or place the pot in a plastic bag and close the opening with a rubber band. A stake or two in the pot or wire hoops will keep the plastic from collapsing on the cuttings.
Plastic bags alone may be used to root cuttings, especially some of the easier to root plants such as chrysanthemums and coleus. Tie a ball of moist sphagnum moss around the base of the cuttings, place them in a plastic bag and close the openings.
Small wooden boxes may be converted into propagation units. The box should be approximately 12 inches (30.5 cm) deep, with the top sloped from one side to the other. Seal cracks or holes in the sides. On the bottom, place a 1 inch (2.5 cm) layer of pea gravel. On top of this place 4 inches (10 cm) of the propagation medium. Moisten the medium, insert the cuttings and cover the top with plastic.
The location of the units will determine to a large extent the success of rooting cuttings. Since each devise is designed to prevent moisture loss, it usually will contain enough moisture to last until the cuttings root. Examine the units frequently, however, and add moisture at any indication of drying.
Temperatures will determine the rapidity of rooting or germination of the seeds. Ideally a temperature of 65°F (18°C) to 75°F (24°C) should be maintained. Keep the units in heated locations during the winter. During warmer times of the year, they may be kept outdoors in a shady location.
Light intensity should be controlled carefully. High light intensity is not desirable–diffused light should be maintained. If units are placed in full sunlight, the temperatures will become too hot inside the sealed units, resulting in damage or death of the cuttings or seedlings. Indoors, the units may be place under fluorescent lights. Lights should be on for 12 to 16 hours a day. Fluorescent aquarium lights may be used on aquariums.
Proper hardening is important. After the cuttings have rooted or the seedling have emerged, they should be exposed to normal conditions in easy stages. Gradually remove the plastic coverings over a period of several days. Removing the covering too suddenly will result in wilting of the plants, injury or even death.