During production, conduct frequent on-site testing of injectors and growing media pH and EC to catch problems before they result in damaging deficiency or toxicity symptoms. Additionally monitor the nutritional status of the crop by the use of comprehensive growing media and tissue testing.
• Media: test at week one after planting and every 4 weeks thereafter.
• Leaf tissue: test monthly after planting; more frequently if you observe problematic symptoms.
Fertilizer Selection
There are a number of fertilizers labeled as “poinsettia fertilizers” and these may or may not be the most suitable ones for your operation. Generally one should look for a high (50 to 85%) nitrate-N fertilizer formulation that provides the correct amount of acidification, calcium and magnesium (based on the specific irrigation water quality). Then supplement your main fertilizer product with components such as STEM, sodium molybdate, and magnesium sources and rotate in calcium fertilizers when appropriate.
Nutritional Goals:
• Maintain growing medium pH between 5.8-6.2.
• Increase root zone pH to 6.5 if irrigation water has a high boron level.
• Avoid high boron level in growing medium (> 0.25 ppm B). Poinsettias can be sensitive to B toxicity that results in leaf edge burn.
• Supply adequate calcium, magnesium and molybdenum levels.
Examples of poinsettia fertilizer programs for pure to moderately alkaline waters with low calcium
| Peters Professional® 18-8-17 Peat-lite® Hi Mag (alternated every 3rd & 5th watering with Peters 15-0-15) |
| Peters 15-5-25 Poinsettia Peat-lite (alternate with Peters 15-0-15) |
| Peters 20-10-20 Peat-lite + Epsom Salts (alternate with Peters 15-0-15) |
| Peters Excel® 15-5-15 + excel 10-0-0 Magnitrate + Peters 15-0-15 |
Examples of poinsettia fertilizer programs for moderately
high alkalinity waters containing fair levels of calcium
| Peters 15-5-25 Poinsettia Peat-lite |
| Peters Excel 21-5-20 + Excel 10-0-0 |
| Peters 18-8-17 Hi Mag |
| Peters 20-10-20 PL + Mg |
If you have additional questions about using Scotts products, contact your Griffin salesperson, or your Scotts Territory Manager at 1-800-492-8255, or visit Scotts Professional Horticulture Web site at http://www.scottsprohort.com.
Fertilizer Concentrations
Growers have in the past few years reduced their fertilizer concentrations from historical levels and in some cases insufficient fertilizer has resulted in N and K deficiencies. For lighter green leafed varieties, we recommend to start off for the first 2 weeks of production at 300 to 350 ppm N on a continuous feed basis (to charge the growing media with nutrients), then gradually reduce levels to 200 to 250 ppm N. Dark leaved cultivars such as Freedom, Prestige, Dynasty Red and Lilo require lower nitrogen rates (100 to 150 ppm) at this point. After bract expansion occurs, further reduce fertilizer concentration to avoid soluble salts build-up in the growing medium. Frequently monitor growing media EC and maintain soluble salts levels below 2.5 to 3.0 mmhos/cm (based on an SME).
Poinsettias will respond favorably to a combination water soluble/controlled release fertilizer (CRF) program. Apply a low rate of Osmocote Plus* 15-9-12 (incorporated at 4 lbs. per yard) as a base feed, then use Peters Excel water soluble fertilizers at half the above recommended concentration (100 to 125 ppm N). The controlled release fertilizer provides some insurance in case something goes awry with the liquid feed program and may also provide some nutrition benefits in the post-production environment.
If you have a mixture of dark and light leafed varieties and are feeding all plants at low fertilizer concentrations, supplemental CRF can also be useful to compensate for the higher nutritional demand of light leafed varieties.
Supplemental Nutrient Treatments to Fine-tune Your Crops
• Calcium (Ca) - low Ca can lead to weak stems and leaf, bract edgeburn and depressed growing media pH. Maintain at least a continuous feed of 60-100 ppm Ca in your feed program. If your irrigation water does not supply enough Ca; add it by using Excel 15-5-15 Cal-Mag or rotating your main fertilizer with Peters 15-0-15. Sometimes even if Ca is adequate in the growing media, the plant due to high temperature or high relative humidity may not take
it up. Weekly foliar spray applications of technical grade calcium nitrate (15.5-0-0) at 0.25 oz. per gal. of spray solution (providing 338 ppm Ca) during bract formation (between first sign of color to until first pollen on flower) may prevent low Ca problems.
• Magnesium (Mg) - low Mg can lead to marginal chlorosis starting on older leaves. Maintain at least a continuous feed of 30-50 ppm Mg in your feed program. If your irrigation water does not supply enough Mg, add it by using Excel 15-5-15 Cal-Mag, Peters 18-8-17 Hi Mag or by supplementing with Peters Excel 10-0-0 Magnitrate or Epsom salts (4 to 6 oz/ 100 gal).
• Molybdenum (Mo) - low Mo can lead to marginal chlorosis and edge-burn on younger leaves especially in late October and November. Avoid this problem by adding Sodium Molybdate September through mid-November on a continuous feed basis at a rate of 1 gram per 100 gal. (to provide 1.2 ppm Mo).
• Micronutrients can be limiting especially if one if feeding dark leafed varieties at low fertilizer concentrations. To avoid micronutrient deficiency symptoms, supplement with a remedial drench of STEM at 1 to 2 oz/ 100 gal on October 1st and November 1st.
Fred Hulme (fhulme@scotts.com) is Director of Technical Services for the Professional Business Group at The Scotts Company LLC.
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