Poinsettia Stock Plants
by Dr. Claudio PasianDepartment of Horticulture and Crop Science
The Ohio State University
Some growers still produce their own cuttings from poinsettia plants. They start growing the cuttings in early spring. For a crop like poinsettias with very low margins and where so many things can go wrong, having a good start is crucial. High quality stock plants will produce high quality cuttings and, in turn, a good poinsettia crop.
Cuttings for stock plants arrive at the time of the year when growers are very busy with bedding crop production and sales. As a consequence, it is not that uncommon to see these cuttings neglected for several days while space is made available to locate them. Get ready before cuttings arrive! Cuttings should be lighted through mid May.
Clean plants come from clean cuttings which in turn come from clean stock plants. From the start, have a pest and disease management program. Be pro-active. If possible, keep the stock plants separated from all other spring crops. This will accomplish two objectives: 1) if there is a pest in your spring crop, it will not move to the poinsettias, or 2) if the poinsettia cuttings are bringing in a problem, it will not spread on your spring crop. Scout plants and sticky traps on a regular basis. If you suffer from lutheoviscopapirophobia, take the necessary steps to cure that, too.
Marathon is commonly used to control white flies. This product should be applied during the later production stages. Old stock plants are too woody for the treatment to be effective. In order to control white flies before the time of Marathon application, use regular spray insecticides.
Many diseases can affect stock plants: Erwinia, Botritis, Rhizoctonia, Powdery Mildew, Pythium, etc. Control of these diseases can be achieved by treating with a variety of chemicals available on the market. Be vigilant and start treating as soon as symptoms appear. Many growers use preventive drenches to avoid root rot.
Stock plants do not require high levels of fertilizer: 200- 250 ppm should do it. Check for adequate levels of Calcium and Magnesium. Monitor pH and electrical conductivity on a regular basis and make adjustments periodically.
If possible, avoid high temperatures (90 F or above). Use some shade and increase air circulation. Good cuttings are produced under good light levels. Jack Williams, from the Paul Ecke Ranch, recommends removing leaves that provide a shady environment for breaking buds. (For more see OFA Bulletin, March 1998.)
Good cuttings are those harvested at the proper level of maturity. Cuttings that are too young take too long to root because they do not have enough reserves and may produce finished plants that are not vigorous. Cuttings that are too old have the same problem due to woody stems. If cuttings produce brown callus, it could be that they are too mature (Figure 1). Overly mature cuttings are more prone to split if not pinched. Proper cutting maturity is cultivar dependent. Most cuttings reach maturity in 5, 6, or 7 weeks after the last pinch of the crop (Figure 2). Ask the company providing you with cuttings for the number of weeks it takes to reach cutting maturity. This information is important for scheduling: select your final pinching date and count backwards using the numbers of weeks it takes to reach maturity for the cultivar you are using. This will determine the dates of cutting harvest.
