The Erik S. Runkle Mist with a fine droplet size on should be applied once the surfaces begin to dry. At each mist- Growing Trends ing event, apply enough mist to nearly cover the leaf but not so Erik S. Runkle is assistant professor and extension specialist, Michigan State University, Department of , A288 Plant and Science Building, East Lansing, MI 48824. much that water drips off the foliage. Excessive misting leaches nutrients from the medium more rapidly and can lead to early nutri- tional deficiencies. • Apply fertilizer. Frequent Successfully propagating misting can rapidly leach out the pre-plant nutrients in most soilless media. Without fertilizer, cuttings cuttings takes planning can become chlorotic and development can be delayed. One way to deliver nutrients to cuttings ore than 1 billion stem cuttings especially during the first seven to is to incorporate a light rate of fertil- of bedding plants, perennials 10 days after cuttings are stuck. izer (such as 40-50 parts per million M and potted plants are propagat- Use of a highly porous rooting nitrogen) into the water used for ed in the United States each year. medium during propagation, such misting. This allows plants to Whether they are purchased from as one that contains at least 50 continue to receive a constant suppliers or harvested from stock percent perlite, can prevent the supply of nutrients and prevents plants, successful cropping requires medium from becoming saturated nutritional deficiencies. Another rapid and uniform rooting of cut- with water. A fine, heavy medium strategy is to drench cuttings with tings. Delayed rooting can increase dries out slowly, which can prevent a fertilizer (200-300 ppm) once problems with insects, diseases and oxygenation of the root zone. Use have developed (for example, nutrition; increase crop timing; and of a porous medium can also 10 days after sticking cuttings for increase variability of starting and reduce problems with fungus many crops). finished material. gnats and shore flies. Plants with • Manage medium and air temper- Successful propagation requires succulent or pubescent stems ature. Temperature influences the starting with high-quality, uniform respond especially well to a light rates of callus formation and root cuttings that are vegetative, not medium during propagation. and development. Ideally, the excessively long and free of • Maintain high humidity. If temperature of the medium should insects, diseases and viruses. humidity in the propagation area be maintained slightly higher Cuttings not of high quality can is maintained at 90-95 percent, (5°F-8°F) than the air so that callus lead to delayed and non-uniform cuttings require less misting. The and root growth occur faster than rooting. Starting with variable humidity can be raised using shoot growth. rooted transplants often produces steam or fog delivered by either To accomplish this, bottom heat- variable finished plants. high-pressure or a fan-driven ing is required. Desirable propaga- water atomizer. In addition, air tion temperatures are 73°F-77°F for Some tips for good crops movement should be minimized the medium and 68°F-73°F for the • Use good sanitation. Successful during propagation so that leaf air. If bottom heat is not available, propagation requires prevention of surfaces don’t dry too quickly. the air temperature should be diseases and viruses. To accomplish • Regulate misting. Stem cuttings increased to 77°F-80°F so that medi- this, employees harvesting cuttings have no roots. so frequent misting is um temperature is adequately high. should disinfest their hands and needed to prevent from drying A high medium temperature wear latex gloves before handling out. Develop a misting program based can be difficult to maintain when stock plants. Cutting tools used on on time, humidity and light levels. cold water is used for misting. To stock plants should be regularly san- Generally, the brighter the light overcome this, increase bottom itized using a disinfestant (such as environment, the more rapidly heating. However, excessive bot- trisodium phosphate) or passed plants dry out. Therefore, cuttings tom heating can create root prun- through a flame. require more frequent misting when ing, in which the temperature at When possible, use new plug exposed to bright light compared to the base of the plug becomes too trays so that there is no chance for at night. high for root growth. Alternatively, pathogens to be resident on the In addition, rootless cuttings dry misting water can be heated or plastic containers. Rooting media more slowly when the relative mixed with hot water to raise its should be free of insects, diseases humidity is high. Once cuttings temperature and thus have less of and weed seeds. Solid benches and begin to root, misting frequency a cooling effect on the medium floors where flats are placed should can be decreased over time. There- temperature. be sanitized between crops when fore, misting should be more • Watch light intensity and photope- possible. Good sanitation protocols frequent during the first week of riod control. Plants that are can prevent crop problems during propagation and when light levels photoperiodic should be maintained propagation. are highest. Once roots have initiat- under noninductive conditions • Use a porous medium. Propa- ed, misting at night can be stopped during propagation so that they are gation requires frequent misting, for most species. not induced to flower.

92 GMPRO August 2006 www.GreenBeam.com For example, cuttings of long- day plants should be grown under a photoperiod of 12 hours or less. Cuttings of poinsettia and other short-day plants need exposure to long days (night length less than 11 hours) to prevent early flowering. Cuttings that contain or develop flower buds during propagation expend some of their energy on the flowers at the expense of root development. Research has shown that the daily light integral (DLI) influences propagation time and root develop- ment. Under a low average daily light integral (less than 3 moles per square meter per day), many cuttings root slowly because they do not receive sufficient light energy. During the initial stages of propagation, a high propagation daily light integral (above 6 mol· m-2·d-1) can also delay rooting. Therefore, a daily light integral of 3 to 6 mol·m-2·d-1 is recommended until roots have formed. Once roots have reached the sides of the plug, 5 to 8 mol·m-2·d-1 of light is suggested. • Establish propagation stages. During propagation, cuttings tran- sition from a completely rootless stem to an actively growing plant. Similar to seedling plugs, cuttings should be managed differently as root development progresses. As cuttings develop roots, they need to be weaned off conditions for lush growth. Misting frequency should be reduced and light levels can be increased. Once roots have filled up half of the plug cell, the humidity can be reduced, misting can be terminated and fertility levels can increase. During the last several days of propagation, plants that are hardened off will perform better after trans- plant. Providing different conditions during the propagation phases can shorten total propagation time and produce high quality, rooted trans- plants. • Other considerations. Other propagation considerations include application of a rooting hormone to the base of stem cuttings. Bacteria, fungi and insects need to be controlled during propagation. High humidity, abundant mois- ture and high temperatures can be conducive to rapid pathogen and insect development and should be actively managed for rapid, uniform rooting without plant loss.

www.GreenBeam.com August 2006 GMPRO 93