How To Screw Up Your Poinsettia CropBy Dr. Dean Krauskopf Don't let the roots get any oxygen. Low oxygen (the same as too much water) around the roots is a great way to either kill them immediately or slow their metabolism down so much that they can't take up nutrients and are susceptible to root rots. "Light" media hold significant amounts of water but the large pores don't retain water so oxygen can move into the media and carbon dioxide move out (roots "breathe"). Low oxygen levels also will do wonders for rooting, especially direct stick. Root formation requires a lot of oxygen so water the media before sticking several times so there is free water in the bottom of the pots. Another good trick is to carefully water the cuttings in after direct sticking. Media snug against the stem is a great way to reduce oxygen movement. Grow them cold. "Who says I should heat the houses during August? It's 80 degrees F or higher during the day and I can just close the vents at night". Karl Trellinger recommends the media should be kept at 72 degrees for optimum rooting. The water coming from your well is probably between 50 and 55 so the media will be colder than recommended, especially in the first critical week or so when you are misting frequently. You can root a crop at lower temps but it will take longer and the longer the cutting is in the propagation beds the more likely root rots, Botrytis, or something else will attack. Plant development, how fast new leaves are produced before flower bud set, is determined by the average 24 hour temperature. If you don't maintain 68 †F degree nights the plants won't have as many nodes so they will be smaller than you want. Small plants in October means trying to push them by increasing temperatures and paying for a lot of fuel. Cyathia drop isn't a problem on most of the new cultivars but if you want to try to make it happen drop night temperatures below 68 †F before the bracts reach full size (looking down on the plant you can't see any green). Too little or too much feed: Nutrients will leach out of poinsettia leaves under heavy mist. As soon as the cutting calluses, it can be fed. I would suggest calcium and potassium nitrate (15-0-15) or comparable at about 50 ppm (NO3-N). I wouldn't apply any fertilizer containing phosphate, especially through a boom, since phosphate applied to the growing point can cause distortion and/or abortion. Contrary to past practice, poinsettias should not be fed at more than 200 ppm nitrate-nitrogen. The dark-leaved cultivars will grow very happily at about 25% less nitrogen than the lighter leaved cultivars. These recommendations are based on about 10% leach and constant feed. Poinsettias will tolerate high levels of soluble salts but the roots are stressed and are more susceptible to root rots and slow development. Since growers have reduced fertilizer rates, I've seen much larger root systems and even some root hairs. One symptom of over fertilization is a sudden growth spurt of dark-leaved varieties right after you stop feeding in November. As salt levels decrease there is less stress on the roots and they take up more nutrients and water - and the plant jumps in height. Don't Use Additional Molybdenum: We're using fertilizers with relatively low ammonium content but I would suggest adding additional molybdenum to your fertilizer tanks even though there is molybdenum in the trace element mix. Most of the trace element mixes were developed for higher fertilizer rates so there might not be enough molybdenum available to prevent ammonium toxicity. Besides it's cheap and it lets me sleep better at night. Don't Apply Growth Regulators Until September: For a compact, well-shaped plant the optimum distance between leaves (internode length) is one inch - from top to bottom. If you see more than an inch in internode length use some form of growth regulation, DIF or growth retardants, even in the propagation bed. If the plant stretches, it will have a weak stem, problems with lower shoot breakage and customers don't like plants they can see through. If more than the first one or two nodes are long, the plant looks like a palm tree. You can plant them deep to make sure they don't flop but then there is a greater chance of root rots. PS: I found the seminar entitled "Proven Production Strategies and Some New Ideas" presented by Karl Trellinger, Fisher USA, Inc., and Jack Williams, Paul Ecke Ranch/Flower Fields at the Ohio Florists' Association Short Course very useful and will be passing some of their information along. If you missed the session there still may be tapes available for sale, contact OFA at 614/487-1117, Email: www.ofa.org |
