Late-summer fertilizing by the numbers

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August is over and just around the corner is the first day of autumn. This is hard to believe with temperatures forecast in the high 80s and low 90s for the next 10 days. I think I must have missed a few months, because I'm just getting into the swing of summer gardening. I didn't fertilize my flowers or veggies enough - so I've been thinking I will give them a good feast this weekend.

But wait; any day now, a frost will hit since the average first frost day is Sept. 15. If I fertilize now, particularly the roses, I will get a flush of new growth. This new growth will just be developing as the frost comes. A frost damaging new growth can set next year's growth back or make roses and others susceptible to diseases and dieback next season.

There is a solution to my fertilization issue, which is to use a fertilizer with a low nitrogen analysis. On any container of fertilizer there are three numbers listed. The first number is the amount of nitrogen, the second the amount of phosphorus and the third number is the amount of potassium. Sometimes there is a fourth number for sulfur.

Nitrogen encourages lush green growth. Phosphorus stimulates flower and fruit production. Potassium builds overall strength, strong roots and good overwintering capacity. Sulfur lowers pH making many macro (nitrogen, phosphorus and potassium) and micronutrients, such as iron, more readily available to the plant.

The higher the analysis of nitrogen, the "hotter" the fertilizer and the more likely it is to stimulate rampant growth or burn plants. Ammonium sulfate's analysis is 21-0-0. It stimulates leaf production, but little else. We definitely want the lowest nitrogen levels possible for flowers and veggies to finish up their growing season.

The nutrient analysis of organic fertilizers is often around 1.5-2-1.5. Although these numbers are low, the fertilizer you apply now won't cause a flush of new growth ready to freeze, but will stimulate final flower or veggie production. It will help perennials and roses be strong and overwinter well.

Organic fertilizers can also be high in beneficial microorganisms that help build a healthy soil, which also helps plants thrive. Inorganic fertilizers such as MiracleGro, Peter's and other brand names often have a nitrogen analysis over 30. These products will really push lush growth, which is not a good idea at this time of year for perennials, trees or shrubs.

Enjoy your final weeks ofsummer!

• JoAnne Skelly is the Carson City/Storey County Extension educator for University of Nevada Cooperative Extension and may be reached at or 887-2252.


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