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The Full Scoop About Fertilizers

  • Nanette Londeree
  • There's a whole lot of confusion when it comes to fertilizers.

    Just check out the shelves at your local nursery or home improvement store. You'll find a mind-boggling array of things to sprinkle, spread, spray on, pour on, mix in, pound in; there's food, meal, pellets, all—in-one, time release, and don't forget the conditioner, compost, mulches and more.

    Are they all fertilizers? Is a fertilizer the same thing as an amendment? A mulch? If not, what's the difference? And what do they do?

    Plants require 17 chemical elements for healthy growth; the four general groups include the essential elements, carbon, hydrogen and oxygen, the primary or macronutrients — nitrogen, phosphorus and potassium, the secondary nutrients — calcium, magnesium and sulfur, and the micronutrients or trace elements — boron, chlorine, copper, iron, manganese, molybdenum, nickel and zinc. These elements are all plant nutrients. Most are already in the air or soil and don't need to be added. Some, like nitrogen, are rapidly used by growing plants and need to be replaced. Others may be present, but unavailable to the plant because of soil or environmental conditions.

    Plants, like people, thrive on a well-balanced diet to keep them at their best. At times, their soil or environment may lack a key nutrient that can be provided as fertilizer, just as we might supplement our diet with a couple of vitamin C tablets if we're not getting enough from fresh fruits and vegetables.

    Contrary to what product labels may claim, fertilizers are not plant food. Plants make their own food using water, carbon dioxide and sunlight. The food they produce, sugars and carbohydrates, are combined with plant nutrients to create the proteins, enzymes and vitamins that are vital to plant growth.

    Let's clarify the terminology:

    • Fertilizers: This is a material added to the environment around the plant that directly impacts the plant, providing it with specific nutrients.
    • Amendments: These are materials mixed into the soil that indirectly aid plant growth by improving the condition of the soil like its texture or water retention.
    • Mulches: These are organic or inorganic materials placed on the soil surface to help prevent weed growth, conserve moisture and add organic matter to the soil as they break down.

    The law requires that manufacturers guarantee the accuracy of what is claimed on a product label — if it's on the tag, it's got to be in the bag. Fertilizers contain active ingredients — the materials responsible for the intended beneficial purpose of the product (think nitrogen or phosphorus). They also can include inert ingredients or filler which are included but have no intended nutritional value. Soil amendments make no legal claims about nutrient content or other helpful (or harmful) effects they may have on the soil and plant growth.

    Inorganic fertilizers are single or compounded chemical elements while organic fertilizers are derived from plant or animals. A complete fertilizer contains all three primary nutrients; an incomplete fertilizer is lacking one or two. There are oodles of forms and formulations of fertilizers available — some of the more common include:

    • Liquids or solids — liquids deliver nutrients to roots immediately and are easy to use. Solid fertilizers are sold as granules, powders or pellets; they can be broadcast, scratched or dug into the soil, or used when planting.
    • Simple or single nutrient fertilizers like ammonium sulfate, urea or superphosphate are relatively inexpensive and generally very concentrated; use with care as they may burn tender growth due to high concentration.
    • Soluble complete fertilizers contain macro, secondary and micronutrients and get to the roots quickly. These chemically based products are very concentrated, so a little goes a long way. You need to dilute them according to the manufacturer's instructions.
    • Slow-release fertilizers are sold as spikes, tablets or bead-like granules that release nutrients gradually over a fairly long period, three to nine months if the soil receives regular moisture. While convenient to use, as you only have to apply once in a season, they may not provide sufficient amounts of the macronutrients and require supplements; they also cost more than other alternatives.
    • Multipurpose products feature a fertilizer plus some other material with a different purpose; most often an insecticide or fungicide is added. This type of product is appropriate if you need the extra ingredient every time you fertilize (which isn't very often), otherwise it is more economical to use fertilizer alone (and gentler on the environment).
    • Natural organic fertilizers — such as chicken, duck or turkey manure, fish emulsion or blood meal — add valuable organic matter to the garden, act slowly with less chance of burning, and are beneficial to microbes though results are less dramatic.

    So, before you reach for an all-purpose tonic for your plants, think about a balanced diet and good nutrition — for you and your plants!