Whether you grow your own stock or purchase unrooted cuttings, propagation will be much smoother when you start with quality poinsettia cuttings and optimum environmental conditions.
For uniform quality, it is important to start with cuttings of the same length, caliper and maturity. Cuttings of different sizes and maturity will root and grow differently. Most poinsettia cultivars root best when harvested about 6 weeks after the last pinch on the stock plants. When taking cuttings, avoid tearing or bruising cut ends. If purchasing cuttings, try to avoid re-cutting the ends as this will open fresh wounds and increase the risk of disease. Each cutting should have 2-3 mature leaves. When sticking the cuttings, only remove those leaves that would be in the rooting medium. For best results, plant no more than 12 cuttings per square foot and arrange the large leaves between the rows so that they do not cover the cutting apexes.
Some stock plant growers place cuttings in a cooler (55°F/ 13°C, at least 90% relative humidity) overnight before planting to remove heat and regain turgidity. If you are not pre-cooling the cuttings before sticking, you will want to get them under the mist as soon as possible to avoid excessive moisture loss.
Poinsettia cuttings root well in a variety of media. Some growers root the cuttings directly in the finishing container while others use rooting cubes, plugs or wedges. Regardless of the choice, the media should be free of insects, disease causing organisms, weeds, or toxic elements. It is also important for the media to have good pore space (about 20%) and water holding capacity (about 50%) and provide physical support for the cutting. Avoid saturating the media as this will delay rooting and increase the risk of fungus gnat and disease problems. Placing the rooting media on sand or other porous surfaces can help wick excess water from the media.
During the early stages of propagation, poinsettias need a constant film of moisture on the foliage. This will probably require some night misting. The frequency and duration of mist will depend on the misting system and the greenhouse conditions. Mist enough to prevent excessive wilting. Excess mist will increase the risk of disease development, leach nutrients from the cuttings and cause stretching. Once the cuttings have callused, reduce the mist as much as possible without letting the cuttings wilt. Callus formation should be evident by day 14. Avoid excessive ventilation early in the propagation cycle as this can dehydrate the cuttings. Once the cuttings have begun rooting, air circulation will help tone the cuttings and get them acclimated to harsher finishing conditions. The cuttings should have a good root system by day 21-27.
Greenhouse temperatures of 80-85°F/ 26-29°C during the day and 72°F/22°C at night are optimum for poinsettia propagation. Shading the greenhouse to 1500-2000 foot candles/16,140 – 21,520 lux will help reduce temperatures and stress on the cuttings.
Some growers dip the base of the cuttings into a rooting hormone. Poinsettias will root without the use of a rooting hormone, especially under optimum environmental conditions. However, the use of rooting hormone may encourage uniform rooting process under less than ideal conditions or with difficult to root cultivars. Growers commonly use 2500 ppm Indole-3-Butyric acid (IBA) or a combination of 1500 ppm IBA plus 500 ppm Naphthaleneacetic acid (NAA).
The use of growth retardant sprays such as Cycocel® or Cycocel® plus B-Nine® will help prevent stretch in propagation. Apply growth regulators early in the morning or in the evening when you can turn off the mist without stressing the cuttings. Make the first application 6-7 days after sticking the cutting. Apply a second spray of growth retardant 4-5 days later, if required. Experiment with 1500 ppm Cycocel® or 1000 ppm Cycocel plus 1000-1500ppm B-Nine®.
Cuttings harvested from well fed stock plants should not require fertilization until roots start to form. Some growers add soluble fertilizer containing 50-100 ppm nitrogen and potassium to the mist for foliar feeding. This requires a good water quality (EC <1.0). Once root initiation has taken place, apply 100-150 ppm nitrogen from a complete fertilizer to the media on a weekly basis until the cuttings are transplanted.
Several insects and disease causing organisms may attack poinsettia cuttings. The most commonly encountered disease and insects in propagation include Botrytis, bacterial soft rot, Rhizopus, fungus gnats and whiteflies. The warm, wet conditions in propagation are excellent for disease and fungus gnat development.
Minimize stress on the cuttings, provide adequate space in propagation and avoid overmisting to reduce the risk of disease development. You can decrease disease spread by removing any infected plant tissue and debris from the greenhouse and disinfecting your hands frequently during the clean-up process. Spray a fungicide on the stock plants before you harvest cuttings to help prevent foliar diseases caused by Botrytis and Rhizopus. Include a copper-based fungicide in the rotation to help reduce the level of Erwinia carotovora, the cause of bacterial soft rot on poinsettia cuttings. Erwinia carotovora thrives under anaerobic conditions found in saturated rooting media. If bacterial soft rot is a common problem during poinsettia propagation, check your water source, as this bacteria has been isolated from some pond water and other water sources.
Fungus gnat larvae injure poinsettia cuttings by feeding on young roots and callus tissue as well as by transmitting root rot diseases. Minimizing stress on poinsettia cuttings and the sanitation practices mentioned for diseased prevention will also help control fungus gnats, as will the elimination of algae and standing water from the propagation greenhouse. If fungus gnats are an ongoing problem, consider the use of preventative treatments.
The best time to control whiteflies is before the cuttings reach propagation. It is difficult to achieve thorough spray coverage on the undersides of poinsettia foliage in propagation. Dipping cuttings in an insecticide may be effective in controlling whiteflies going into propagation, however, check for phytotoxicity before treating large numbers of cuttings. Once the cuttings have enough roots to be self-sufficient, smokes, fogs or aerosols may be used to control whiteflies. For these materials to work without causing phytotoxicity, foliage must not have free moisture at the time of application.
After the cuttings have rooted, it is time to acclimate them by eliminating automatic mist and by increasing air flow and light levels. Keep some greenhouse shading to reduce light and heat stress until after the plants have been pinched. Additional humidity and occasional syringing or misting will prevent excess water stress and keep the plants soft for good branch development.
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