Last week, a caller wanted to know if it was too late to fertilize roses. It was a very good question because we want to slow down growth toward the end of summer, but fertilization speeds up growth.
New growth is very susceptible to freeze damage, and freeze-damaged roses are susceptible to disease. Our average first frost date is Sept. 15.
Avoid using fertilizers high in nitrogen 30 to 45 days before the first frost, about where we are now. Instead, now is a good time to feed roses with a fertilizer higher in phosphorous and potassium. This will produce a longer bloom cycle.
Choose a fertilizer that contains micronutrients, such as iron, calcium and sulfur, as well. On a fertilizer container, the "analysis," the three numbers listed, tell you the percent of the nutrients nitrogen, phosphorus, potassium, in that order. Nitrogen produces leaves. Phosphorus develops a good root system and increases flower production. Potassium keeps plants vigorous. The American Rose Society recommends a fertilizer with close to a 6-12-6 analysis for roses during late summer.
Apply slow-release fertilizers this time of year. Inorganic fertilizers are generally fast-release, and organic ones are generally slow-release. What are some organic fertilizers? Compost is organic, but is usually considered an amendment rather than a fertilizer because the nutrient analysis is very low, about 0.5 percent nitrogen, phosphorus and potassium. Although compost may not supply many nutrients, it does build up soil, allowing all the beneficial organisms to make the rose a stronger plant. Fish meal (5-3-3), fish emulsion and kelp meal (1.5-0.5-2.5) are additional organic products.
Alfalfa tea is another organic nutrient source. Make alfalfa or compost tea by adding 10 to 12 cups of alfalfa meal, alfalfa pellets or compost to 30 gallons of water in a 32-gallon plastic garbage can with a lid. Stir the mixture and let it soak for four or five days, stirring occasionally. The tea will start to smell in about three days, so keep the lid on. Then, use about a gallon of this mix on large rose bushes once a week, irrigating on your regular schedule the rest of the time. One load of meal or pellets will brew up two full barrels.
There are some slow-release inorganic fertilizers available. Fertilizers, whether organic or inorganic, are packaged in a granular or liquid form. Some are concentrated and need to be added to water for application as a spray or a soil drench.
Fertilize lightly and enjoy your blooming roses for a bit longer.
For more information, e-mail skellyj@unce.unr.edu or call me at 887-2252. You can "Ask a Master Gardener" by e-mailing mastergardeners@unce.unr.edu or call your local University of Nevada Cooperative Extension office. Check out many useful horticulture publications at www.unce.unr.edu.
• JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension.