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THE FULL SCOOP ABOUT FERTILIZERS -
SO MANY CHOICES!!!
by Nanette Londeree, Master Rosarian

If you’re shopping at a nursery or home improvement center for fertilizers, you can be faced with a bewildering array of different forms and formulas. Before you pull out your wallet, have an idea of what you are trying to achieve with the product - improve the soil, correct a deficiency, or simply provide general nutrition. Do you want to add it to the soil or spray it on the plant? Does it matter if it’s chemically synthesized or are you sticking with organics? Getting a clear idea on what you want the fertilizer to do and how you want to use it will help make your selection easier.

What’s on the label

Chart Believe it or not, fertilizer labels are regulated and they include a lot of terminology; a fertilizer active ingredient is the specific material responsible for the intended beneficial purpose of the product while inert ingredients (often referred to as filler) are substances other than an active ingredient intentionally included in a fertilizer but have no intended nutritional value. Chemically based fertilizers are simple compounds derived from naturally occurring chemical elements; nitrogen from the atmosphere is synthesized to create ammonia and urea, while phosphate and potassium (potash) are from mined deposits. Naturally-based fertilizers are derived from organic materials - bone meal, kelp meal, fish emulsion and manure are commonly used organic fertilizers.

Fertilizer Chart A product labeled as a fertilizer guarantees the minimum percentages of the primary nutrients - nitrogen, phosphate and potash, identified on the label and present in the stated amounts in the container. In some cases, a fertilizer will contain secondary nutrients or micronutrients not listed because the manufacturer does not want to guarantee their exact amounts. The relative amount of each macronutrient is listed as a percentage of the total on the fertilizer package label, always in the same sequence – nitrogen, phosphorus and potassium. A fertilizer that is 10-20-10 contains 10% nitrogen, 20% phosphorus and 10% potassium, or a total of 40% active food value (10+20+10), with the remaining 60% of the mixture made up of inert, inactive material that is generally of little or no practical value from the fertilizer standpoint. The ideal N-P-K proportion for roses is 1:2:1.

Chemical vs organic

There’s an ongoing debate about the pros and cons of chemical vs organic fertilizers. Does a plant know or care what the source of the elements is? Chemically based fertilizers come in a wide variety of concentrations and formulations, are generally convenient to use, readily available, provide rapid results and are the cheapest sources for the three macronutrients. On the flip side, the macronutrients can be rapidly leached during periods of heavy rain or irrigation (ending up in groundwater and runoff), chemical salts can build up in the soil following heavy applications over long periods of time and many formulations contain little or no trace elements thus requiring addition of supplemental materials.

Most of the nutrients in organic fertilizers are not water soluble and are found in low concentrations; they are broken down by soil microbes and released to the plant slowly over a period of months or even years. They can serve as both fertilizer and soil conditioner, improving soil structure and building the populations of beneficial soil organisms, and add valuable trace elements. There is a minimum loss of nutrients through leaching, and little accumulation of chemical salts so they are much less likely to burn roots than more concentrated chemicals. Organic fertilizers may contain pathogens and other disease causing organisms if not properly composted, their nutrient contents are variable and their release to available forms that the plant can use may not occur at the right plant growth stage. Also, the difficulty in obtaining some of the materials and their potentially objectionable odor may be disadvantages for this type of fertilizer.

How About Epsom Salts?
Epsom salts (magnesium sulfate) helps produce lush new canes and rich green foliage – fact or fiction? Rosarians have been extolling its virtues for ages. It can improve the health of your roses if they are growing in soil deficient in magnesium. Roses are sensitive to salts, so the concentration of magnesium should not exceed 100 parts per million (ppm). Soils deficient in magnesium (less than 20 ppm) may exhibit leaves where the center is green and the edges yellowed. Before making your trip to the drug store, purchase a soil test kit and see if you really need to add it.

Available Forms of Fertilizers

Once you have decided what elements you want to apply to your roses, you should consider the different forms that each may come in. Whichever material and method you use to fertilize, liquid or dry, simple or multinutrient, chemical or organic – don’t try to second guess the manufacturer - follow the directions. Too much of a good thing, even manure, can be potentially hazardous to your plants.

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 (21-0-1), urea (46-0-0) or superphosphate (0-20-0), are relatively inexpensive and generally very concentrated; they take up little storage space, but may burn tender growth due to high concentration.

Fertilizing Soluble complete fertilizers like MiracleGro and RapidGro, 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. Mill’s Easy Feed is a unique (and potent!) blend of organic and inorganic materials; Epsom salts, chelated iron, soluble seaweed extract, fish soluble, urea and other soluble fertilizers.

Slow-release fertilizers are sold as spikes, tablets or bead-like granules that release nutrients gradually over a fairly long period, 3 – 9 months if the soil receives regular moisture. Products like Osmocote are very convenient to use as you only have to apply once in a season. They may not provide sufficient amounts of the macronutrients and may require supplements, and cost more than other alternatives.

Multipurpose products feature a fertilizer and some other material with a different purpose. The most common is a combination of fertilizer and insecticide or fungicide such as Bayer Advanced ™ All-in-One Systemic Rose and Flower Care. This type of product is appropriate if you need the extra ingredients every time you fertilize, otherwise it is more economical to use fertilizer alone (and gentler on the environment). Another type of multipurpose fertilizer contains other growth enhancers; Dr. Earth Rose & Flower Fertilizer is a blend of cottonseed meal, fish bone meal, fish meal, alfalfa meal, kelp meal, mined potassium sulfate, soft rock phosphate, seaweed extract and seven champion strains of beneficial soil microbes plus ecto- and endo-mycorrhizae.

Natural organic fertilizers like MaxSea, fowl 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.


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Last Modified: 08/06/2013