Problem may not be fertilizer, but incorrect pH
E1 salts to our soil. They can also inhibit natural soil organisms, and they have the potential to burn our rose bushes.
When our plants are ‘not quite right’
When we feel out of sorts, we often reach for comfort food to help us feel better. When something is “not quite right” with our roses, our first response is often to add more fertilizer to perk them up. After all, if food can help us feel better, surely it will do the same for our roses. But what we apply to our soil is not necessarily what our roses need or what they are able to use. When we add too much of one nutrient, such as phosphorous or epsom salts (magnesium), other micronutrients can become unavailable to the plant. In addition, when plants lose their vigor or have smaller blooms or leaf abnormalities, the problem might be not a fertilizer deficiency. It might be an incorrect pH, which prevents our plants from properly taking nutrients from even a nutrient-rich soil.
Overfeeding can do more harm than good
Linda Chalker-Scott, Ph.D., associate professor and extension urban horticulturist at Washington State University, calls overused phosphorous fertilizer plant “junk food.” She says there is no scientific evidence that roses need high levels of phosphate or potassium. She cautions that an overabundance of these nutrients can be detrimental to our soil and limit the uptake by the plant of other essential nutrients such as iron, manganese and zinc. Overfertilizing with phosphorus can also disrupt beneficial mycorrhizae, a root fungus that helps feed the plant. The fertilizer industry has mycorrhizae
to sell us, but where indigenous mycorrhizal species can’t survive, adding packaged mycorrhizae won’t help our plants and is a waste of money.
How much do we really need?
Each year for the last 20 years, I fertilized my roses with an organic granular fertilizer several times a year. Sometimes, I used Ada Perry’s Magic Formula 2.5-2.5-1, other times I used BioStart 3-4-3, Dr. Earth 4-6-2 or E. B. Stone 5-6-3. They are all good organic products, with low levels of NPK, and they all have additional micronutrients specific to the needs of roses. I felt virtuous and dutiful, and I was convinced my roses felt loved.
Three years ago, I did a soil test and the soil results showed that I had excessive amounts of phosphorous and potassium in my soil. This, even though none of the organic products I used contain high amounts of these nutrients. It was a matter of accumulating too much phosphorous and potassium year after year
until I had an excess. Our soil and the millions of organisms that inhabit our soil are so complex. It now seems presumptuous to me to apply fertilizers without periodically doing a soil test and adding only what is necessary.
When people would ask me, “What fertilizer do you recommend for my roses?” my answer usually included one of the above-mentioned products. Or I would suggest that the grower review fertilizer label ingredients and select a product with organic ingredients such as blood meal, bone meal, fish meal, kelp meal, cottonseed meal and alfalfa. Today, I preface these recommendations with the suggestion that the gardener get a soil test, because nothing can beat a personalized scientific answer.
How to get a personalized scientific answer
Sending a soil sample to a soil laboratory is simpler and less costly than it sounds. I have used A&L Great Lakes Labs — (260) 483-4759 — for the last three
years. It is an independently owned and operated agricultural testing laboratory located in Fort Wayne, Ind. Their website, algreatlakes.com/pages/lawngarden-sampling, explains how to collect your soil sample and provides the form you submit with your soil. I use them because they charge only $35, way less than the laboratories in California. They test for key nutrients, and they also test your soil pH.
The ideal pH for roses is a soil that tests between 6.0 and 6.5. You receive a written
detailed breakdown of the nutrients in your soil and comprehensive recommendations on fertilizing.
Nitrogen should be added to the soil periodically throughout the growing season as nitrogen is very mobile and depletes quickly. For the past three years based on the recommendations of my soil test, this is the only nutrient in the form of blood meal that I have applied to my soil every few months. This personalized regimen has saved me a lot of time and money, and my roses are
healthy and vigorous.
How we fertilize our gardens does not need to remain static and repetitive. To keep our soil healthy and to allow our plants to obtain the nutrients they need, we should shift our fertilizing regimen from “I have always done it this way” and “more must be better” to a new thoughtful regimen based on the recommendations of science.