Master gardener Paul James is often asked to clarify statements he has made about choosing and using fertilizers--a subject that continues to confuse even experienced gardeners. He has talked about fertilizer before but has always fallen short of saying exactly what he wanted to say--chiefly because he didn't want to spark controversy. He has decided to present his true feelings about fertilizer in a slightly twisted Q&A style. This time he asks the questions and also gives the answers:
Q: Plants need fertilizer to grow, right?
A: Fertilizers don't make plants grow. The sun makes plants grow--thanks to a process known as photosynthesis. Fertilizers are merely nutrient additives that may or may not actually be necessary, depending on what you're growing. The plants in my perennial garden are healthy and lush, and they're free of insect and disease problems. The foliage plants show no signs of any nutrient deficiency, and the flowering plants are flowering rather prolifically. I have never fertilized these plants. The only nutrient boost these plants have received has been in the form of compost (applied at planting time and at the beginning of the growing season) and a thick layer of mulch, which has slowly decomposed to release even more nutrients. You can have a great-looking perennial garden and healthy plants that resist insect and disease attack without conventional fertilizers. If I were to fertilize these plants, they'd probably produce too much tender foliage, which is what bugs enjoy most. They'd also need more water, and that's something I'm trying to cut back on.
Q: What about all the other plants in the landscape? Don't they need fertilizer?
A: The truth is most types of plants will grow great with little or no conventional fertilizer if the soil is routinely amended with compost and topped with an organic mulch. That applies to all kinds of plants--turf grasses, trees, shrubs, flowers and vegetables.
Q: Where do plants get the nitrogen, phosphorous and potassium (NPK) they need for optimum growth?
A: The whole NPK issue is far too simplistic, because it ignores the fact that plants also need all sorts of micronutrients rarely found in conventional fertilizers. It also causes gardeners to lose sight of the most essential ingredients for soil fertility--namely, carbohydrates, cellulose, other organic matter, bacteria, fungi and other ingredients that make up the soil food web.
Q: What's wrong with adding a balanced fertilizer, such as 10-10-10?
A: For one thing, 10-10-10 isn't a balanced fertilizer. In general, plants use nitrogen, phosphorous and potassium in a 3-1-2 ratio. A truly balanced fertilizer would have that ratio. When I use fertilizers, I use only organic products with that ratio or a multiple of it, such as 6-2-4. Even then, I only use half of what the manufacturer recommends.
Q: Do you use fertilizers?
A: Absolutely, but I use them primarily on vegetables and fruits (in addition to loads of compost and green manure crops) to sustain higher yields. I also fertilize my lawn once or twice a year with a slow-release, organic product. I top-dress it with sifted compost, which also serves to fertilize nearby trees and shrubs.
Q: Can fertilizers harm plants?
A: Absolutely. In fact, I'm convinced that plants suffer from too much fertilizer rather than not enough, and that includes both chemical and organic fertilizers. Excessive fertilization can backfire on you by stunting or burning plants. It can make them more susceptible to disease. In my opinion, fertilizer is not as necessary as we have been led to believe; using less fertilizer and more compost will result in healthier plants with fewer insect and disease problems. You will also have healthier soil.
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