The fertilizer industry inundates us with countless long lists of "must have" products for roses. Peer referrals often require tedious applications that cost a lot of money and consume a lot of effort and time. If we use too much fertilizer, can we do more harm than good? How many do we really need?
Plants need nutrients for strong and healthy growth, including three major macronutrients, namely nitrogen, phosphorus and potassium (NPK). When we add organic fertilizers and organic amendments to our soil, we rely on the activity of millions of micro-organisms, microbes, fungi, insects and worms in the soil. The result is fertile, healthy soil that slowly releases nutrients at lower concentrations over longer periods of time and keeps our plants strong.
Devotional rosaries often add fertilizer to our soil throughout the year. Some of us add too much. Some of us use high phosphorus (P in NPK) fertilizers, which are said to help roses produce more flowers. Fertilizers increase nutrient levels, but using large, unnecessary amounts of fertilizer can affect the health of our soil, the health of numerous underground organisms, and their contribution to our soil. High concentrations of chemical fertilizers add salt to our soil. They can also inhibit natural soil organisms and potentially burn our rose bushes.
When Our Plants Are "Not Quite Right"
When we feel down, we often reach for comfort food to make us feel better. When something "goes wrong" with our roses, our first reaction is often to add more fertilizer to revive them. After all, if food helps us feel better, it must do the same for our roses. But what we apply to our soil is not what our roses need or can use. When you add too much of a nutrient like phosphorus or Epsom (magnesium) salt, other micronutrients can become unavailable to the plant. Also, when plants lose vigor or have small flowers or leaf abnormalities, the problem may not be a lack of fertilizer. This can lead to incorrect pH, which prevents our plants from absorbing nutrients properly, even from nutrient-rich soil.
Eating too much can do more harm than good.
Linda Chalk-Scott, Ph.D., a professor and urban extension horticulturist at Washington State University, calls excess phosphorus plant fertilizers "fast food." He says there is no scientific evidence that roses need high levels of phosphate or potassium. He warns that an excess of these nutrients can be harmful to our soil and limit plant uptake of other important nutrients such as iron, manganese and zinc. Overfeeding with phosphorus can also interfere with beneficial mycorrhizae, the root fungi that help feed plants. The fertilizer industry has mycorrhizae to sell us, but where native mycorrhizal species cannot survive, adding packaged mycorrhizae will do our plants no good and is a waste of money.
How many do we really need?
Every year for the past 20 years I have fertilized my roses with a granular fertilizer several times a year. Sometimes I use Ada Perry's Magic Formula 2.5-2.5-1, other times I use Biostart 3-4-3, Dr. Tierra 4-6-2 or EB Piedra 5-6-3. All are good organic products, with low NPK levels, and all contain additional micronutrients specific to rose needs. I feel virtuous and honored and I'm sure my roses feel loved.
Three years ago, I did a soil test and the soil results showed that my soil had excessive amounts of phosphorus and potassium. This, despite the fact that none of the organic products I've used are high in these nutrients. It was a matter of accumulating too much phosphorus and potassium over the years until you had a surplus. Our world and the millions of organisms that inhabit it are incredibly complex. Now it seems presumptuous to apply fertilizer without checking the soil periodically and adding only what is needed.
When people ask me, "What fertilizer do you recommend for my roses?" My answers usually include one of the products listed above. Or I would suggest that growers check fertilizer ingredient labels and choose products with organic ingredients such as blood meal, bone meal, fish meal, algae meal, cottonseed meal and alfalfa. Today, I preface this recommendation with a suggestion that gardeners test the soil, because nothing beats a personalized scientific answer.
How to get personalized science answers
Sending soil samples to a soil laboratory seems easier and less expensive. I have been using A&L Great Lakes Labs - (260) 483-4759 - for the past three years. It is an independently owned and operated agricultural laboratory located in Fort Wayne, Indiana. Their website, algreatlakes.com/pages/lawn-garden-sampling, explains how to collect your soil sample and provides a form to submit with your soil. I used them because they were only $35, much cheaper than the labs in California They look at key nutrients and test soil pH.
The ideal pH for roses is a soil that is between 6.0 and 6.5. You'll get a detailed written breakdown of the nutrients in your soil and comprehensive fertilizer advice.
Nitrogen must be added to the soil periodically throughout the growing season because nitrogen is highly mobile and degrades quickly. For the past three years, based on my soil test recommendations, this is the only blood meal nutrient I apply to my soil every few months. This custom method has saved me a lot of time and money and my roses are healthier and stronger.
The way we cultivate our garden should not be static and repetitive. To keep our soil healthy and our plants getting the nutrients they need, we need to change our fertilizer rules from "I've always done it this way" to "there should be more." Better" in a new weight-based regimen. On science. Recommendations
Parwich is a member of the Rosa Society of San Diego , a Rosarian Consultant and a UC Cooperative Extension Master Gardener .
This story originally appeared in the San Diego Union-Tribune.
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