Why use intermittent mist?
Using intermittent mist to root cuttings of woody ornamentals and perennials is one of the most efficient means of asexually reproducing large quantities of plants. Intermittent mist offers a means of automatically supplying moisture during the critical periods of propagation by using timers that control the delivery of the misting water on a precise schedule. Without intermittent mist, cuttings need to be kept in a humidity and temperature controlled environment to keep them from wilting and dying from overheating and transpiration. Transpiration is the evaporation of moisture from a plants leaves, stems, flowers, and roots. Intermittent mist raises the humidity level around the cuttings, which lessens the transpiration process and allows the cuttings to form a callus and root, and reduces the temperature around the cuttings. All this can be accomplished without the need of an expensive greenhouse which requires temperature and humidity controls.
Under ideal conditions, certain softwood cuttings can root under intermittent mist in as little as 2-3 weeks, allowing you to root multiple batches of cuttings in a single growing season.
There are many variations on misting facilities, and one style does not fit all. Large propagators may use large misting houses with elaborate lighting and plumbing, while smaller family owned nurseries may use simple hoophouses or root the cuttings in sand beds right outdoors using simple misting systems and natural lighting.
Proper location of an outdoors misting area is extremely important for success. Too much sun or wind can be very detrimental to the cuttings. Filtered shade throughout the day is best, as is a location out of direct wind, but these can be overcome with artificial shade and baffles to deflect the wind. A simple structure can be built around the misting area and shade cloth or lattice can be used with great success to reduce the sun and wind.
The proper rooting media is critical when rooting cuttings under intermittent mist. Sand has been used with great success for many years, however, a mixture of peat moss with an equal amount of perlite, vermiculite, or sand is an even better rooting medium. The peat/perlite, peat/vermiculite, or even a peat/sand mixture is superior to sand alone because it will be more porous, well aerated and better drained than sand alone.
The correct duration and interval of mist is critical to the ability of the cuttings survival and success at rooting. Too little mist or too much time between mists will result in the cuttings drying out, wilting and dying. Too little mist will also result in the cuttings overheating which will also result in the cuttings dying. Too much mist or too little time between mists will result in a constantly wet cutting and constantly wet rooting medium. This will result in leaf drop, stem rot, and fungus and diseases. A good basic starting point is a 5 to 10 second misting period every 5 to 10 minutes.
One factor often overlooked while rooting cuttings is the temperature around the cuttings. Air temperature should be kept between 50°F and 69°F. Slightly higher air temperatures will not harm the cuttings, but lower temperatures can be detrimental to the cuttings. The rooting medium ideally should be kept between 65°F and 75°F to promote callusing and root development. One way of maintaining proper medium temperature is through soil warming cables placed under the medium. These cables will automatically maintain the proper temperature of the medium, creating ideal conditions for callus forming and root development. A plant develops roots as long as the medium temperature is above 45°F, so maintaining the temperature of the medium above 45°F can greatly increase the ability of the cuttings to form roots.
Care of a rooted cutting
After the cuttings have developed roots, the frequency of mist should be gradually reduced to begin hardening off the cuttings and to get them accustomed to normal growing conditions. Over the period of a month or so, the water should be reduced to a once a day watering. The cutting are now ready to be transplanted into pots, grow beds, or planted into the landscape. Potted plants should continue to be watered once a day. The new plants in grow beds or planted in the landscape should be watered once a day for a few weeks, then once every two or three days for a few weeks. After about a month, the plants should established enough to be watered only during long dry spells.