Fertilizing Roses

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By Rosarian Marilyn Maloney

 

“For everything there is a season ... "   

 

 ... and for fertilizing roses in the upper plains of South Dakota September 1 means:  STOP.  Use Labor Day as a target for a reminder--Let those precious plants slow down and get ready for winter. 

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So much for stopping—this article is intended to discuss the basics of fertilizer and fertilizing rose bushes.  Roses are heavy feeders.  They can survive without being fertilized but they will struggle.  To perform their best, roses need a continuous source of nutrients during the growing season not only to provide lush blooms, but to fend off insects and disease.

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So, what do we need to know to keep our babies healthy and productive? 

 

CHECK SOIL PH FIRST

First, just adding fertilizer – organic or inorganic - to the soil -doesn’t guarantee success.  To be best able to absorb nutrients, roses need soil with a pH of 6 to 6.5.  (See Hobart Kitchen Gardens chart.)     Or 6-7 according to PW Proven Winners.  Soil in our upper plains area generally runs higher, more alkaline, in the 7-8 range which means we are apt to need to lower our pH to get the most from any fertilizer. When the soil pH is outside mid-range soil nutrients become chemically bound to soil particles thus unavailable to plant roots.

 

 What is the pH of your beds?  If you don’t have a number, it’s time to test.  Either send in soil sample to a testing lab, (SDSU list at end of this article) or use a meter.  Three-way meters that check pH, moisture, and light are available online or locally for $10-$12.   Once you know what your pH numbers are, you can amend your rose bed as needed.  To lower an alkaline soil John Turek, president of the Twin Cities Rose Club, suggests using 1 pound of ground up sulfur per 100 sq feet or add naturally acidic organic material such as conifer needles sawdust, peat moss or oak leaves.  To raise an acid soil, add 3-4 lb. limestone per 100 sq ft.  The goal is the mid-range of 6-7. 

 

John also suggests changing soil pH should be done gradually, over a couple of growing seasons and monitoring yearly after that. 

Once soil pH is under control it’s on to actual feeding either for routine maintenance or to correct a specifically identified deficiency.  Roses need the primary nutrients- Nitrogen, Phosphorous, and Potassium as well as the macronutrients-calcium, magnesium, sulfur, boron, copper, iron, manganese, and zinc and will tell the observant gardener if they aren’t getting enough.   The following will get you started:  

                                                                                                                                               

 ---Nitrogen (N):   promotes healthy leaf growth which results in more and larger blooms.  Too much nitrogen results in too much foliage which reduces blooms; too little and leaves to have a uniform light green color starting at the bottom of the plant that progressively turn more yellow, plant growth is stunted, and bloom size is reduced.                                                                     

 

 ---Phosphorus (P): promotes heathy root system that makes for lots of blooms.  Too little phosphorus leads to leaves at the bottom of the plant turning purplish, leaf drop, weak stems and buds that don’t open.          

                                                                                   

---Potassium /potash (K): is the plant’s first aid when stressed by disease, insects, or harsh weather.  Tell-tale signs a plant is low on potassium are yellow and browning leaf margins starting on older leaves first, weak stems, and buds that don’t open.

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UP-DOWN-AROUND

One helpful way to keep track of which element does what is the acronym, “Up-Down-Around:”

Up-Nitrogen-Leaves. Down-Phosphorus-Roots. Around-Potassium-General well-being.

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In addition to the macro-nutrients listed above we need to keep an eye out for deficiencies in the micro-nutrients listed on the Nutrient Availability graph.

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-Magnesium-older leaves cup down, are smaller, show chlorosis between veins.

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-Sulphur-leaves light green with lighter green veins.

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-Calcium-new leaves distorted, older leaves become dull green or curl down at margins

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-Iron-May be an alkaline pH issue, common in our area.  First shows up on upper, new leaves-veins show green with rest yellow. 

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-Manganese-interveinal chlorosis in leaves

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-Molybdenum-new growth looks wilted, tip scorching on leaf tips. 

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When fertilizing to correct a particular deficiency its back to basics.  Check the pH to make sure nutrients can get through to the root system.  Then update the soil test to see if there is more than one issue and apply an all-purpose fertilizer or single purpose nutrient as appropriate.  Locally often it’s iron and a chelate of iron foliar spray is a quick fix. 

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For newly planted roses, PW Proven Winner suggests amend the hole with organic matter, work in a slow release fertilizer and a handful of bone meal for root development. ¼ to ½ cup Epsom salts around the base will promote cane and leaf development.  Continue to fertilize every 3-4 weeks with mild fertilizer such as fish emulsion. (One of our local stores has a gallon for $18.00)   If a newbie dries out full strength fertilizer can cause leaf and root burn.

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For routine maintenance other than rugosas and the species roses that don’t want or need fertilizer or fungicides, established roses will benefit from the application of a mild fertilizer early in the spring before and in preparation for the first bloom, and again after the first bloom. This is especially effective for repeat bloomers.  Once bloomers only need the first application.

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CHOOSING A FERTILIZER

What fertilizer to use is a whole other topic but for starters, when shopping for a fertilizer the magic information, N-P-K, that’s on every bag tells us the amount of Nitrogen, Phosphorous, and Potassium in the package. These are macro nutrients-the top three on the soil pH chart.  The higher the number the stronger the concentration.

 

Fertilizer numbers can be used to figure how much fertilizer needs to be applied to equal one pound of the nutrient you want to add to the soil.  Start with 100.  If the package shows 20-10-5 the concentration of nitrogen is 20 or twice as much as phosphorus at 10, and four times as much as potassium at 5.  To figure how much fertilizer is needed to add a pound of a nutrient (N-P or K) to the soil, start with 100 and divide by the number for the nutrient. In this case 100 divided by 20 for Nitrogen equals 5 or five pounds of this product will add one pound of Nitrogen to the soil; 100 divided by 10 equals 10 or ten pounds of this product will add one pound of Phosphorus to the soil; and lastly 100 divided by 5 equals 20 or twenty pounds of this product will add one pound of Potassium to the soil. 

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Organic or not is your call.   One of my science professors at Northern stressed, “Nitrogen is nitrogen.  Plants don’t distinguish.”  He also was in favor of using at least some compost or well-rotted manure to maintain or improve soil structure. 

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With fall upon us and our “STOP” in place, the above is food for thought for spring 2022. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

                      In this case 100 divided by 20 for nitrogen equals 5 or five pounds of this product will add one pound of nitrogen to the soil; 100 divided by 10 equals 10 or ten pounds of the product will add one pound of phosphorus to the soil and lastly 100 divided by 5 equals 20 or twenty pounds of product to add one pound of potassium to the soil.                                                                        Read more at Gardening Know How, https:// www.gardeningknowhow.com/garden-how-to/soil-fertilizers/fertilizer-numbers-nkp.htm.

 

 

-Zinc-twisted distorted new growth

-Copper-new leaves develop light edges

-Boron-new growth ceases or withers, leaves do not develop or are distorted.

(above summary from ARS article by Rita Perwich, Consulting Rosarian, San Diego Rose Society, Roses & You, June 2020.)

 

When shopping for a fertilizer the magic information, N-P-K, that’s on every bag tells us the amount of Nitrogen, Phosphorous, and Potassium in the package.  These are macro nutrients-the top three on the soil pH chart.  The higher the number the stronger the concentration. Fertilizer numbers can be used to figure how much fertilizer needs to be applied to equal one pound of the nutrient you want to add to the soil.  Start with 100.  If the package shows 20-10-5 the concentration of nitrogen is 20 or twice as much as phosphorus at 10, and four times as much as potassium at 5.  To figure how much fertilizer is needed to add a pound of a nutrient to the soil, start with 100 and divide by the number for the nutrient.  In this case 100 divided by 20 for nitrogen equals 5 or five pounds of this product will add one pound of nitrogen to the soil; 100 divided by 10 equals 10 or ten pounds of the product will add one pound of phosphorus to the soil and lastly 100 divided by 5 equals 20 or twenty pounds of product to add one pound of potassium to the soil.

Read more at Gardening Know How, www.gardeningknowhow.com/garden-how-to/soil-fertilizer