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Fertilizer Buying Guide

Choosing fertilizer can be a challenge. Three of the elements necessary for lawn and plant growth are oxygen, hydrogen and carbon. These are all available from the environment. However, plants also need nutrients that aren't as readily available. Nutrients don't stay long in the soil and have to be replenished regularly. Each nutrient plays an important role in plant survival and health. Fertilizer is the means of supplying these nutrients.


Necessary Plant Nutrients

The nutrients are divided into three categories:

  • Macronutrients: Nitrogen, phosphorus and potassium are the primary nutrients critical to plant health.
  • Secondary Nutrients: Calcium and magnesium are needed in lesser quantities but are still necessary for optimum plant growth.
  • Micronutrients: Boron, chlorine, cobalt, copper, iron, manganese, molybdenum, nickel and zinc round out the list.


Fertilizer Types

Fertilizer is available in two types: liquid and granular. Choose the one that meets your needs in the form that's easiest for you to use:

  • Liquid fertilizers are fast-acting. Since they're quickly absorbed, they require application every two to three weeks. Most are concentrates, mixed with water prior to application by a hose-end sprayer or a watering can.
  • Granular fertilizers are applied dry and must be watered in. Granular fertilizers are easier to control because you can actually see how much fertilizer you're using and where it's being dispersed. They're normally applied with mechanical spreaders.

Granular fertilizers are produced in two different formulations: quick-release and slow-release.

Quick-release fertilizer typically lasts for three to four weeks, depending upon the temperature and the amount of rainfall. For general use, these water-soluble nitrogen fertilizers (WSN) are also known as commodity or field grade fertilizers.

There are two main types of slow-release fertilizers, known as water-insoluble nitrogen (WIN), available for specific applications:

  • Sulfur-coated, which lasts for about 8 weeks.
  • Polymer-coated, which lasts for about 12 weeks.

Both time estimates may vary depending upon the amount of rainfall.



How to Read a Fertilizer Label

Fertilizer

The three numbers (often called NPK) on a fertilizer package tell you the percentage of the primary nutrients' makeup by weight. These percentages in fertilizer compounds are formulated for everything from asparagus to zinnias. The three main components are:

  • Nitrogen (symbol N) for leaf development and vivid green color
  • Phosphorous (symbol P) for root growth
  • Potassium (symbol K), sometimes called potash, for root development and disease resistance

For example, a bag marked 16-4-8 contains 16% nitrogen, 4% phosphorous and 8% potassium. The other 72% is usually inert filler material, such as clay pellets or granular limestone. To know how much of each is in the bag, multiply the percentage by the size (weight) of the bag. (Example: A 50-pound bag of 10-10-10 contains 5 pounds each of nitrogen, phosphorus and potassium). There may also be secondary or minor elements in the formula. Don't feel shortchanged by the presence of the so-called inert material in the fertilizer bag. Its purpose is to help distribute the fertilizer evenly and prevent chemical burn.



Plant Foods

Included in the fertilizer family are the general or all-purpose plant foods. In addition to granular or liquid form, they're also available as tablets or spikes.

Plant foods are usually in smaller, more manageable packages for use with houseplants. You'll find specially formulated plant foods for indoor plants, like African violets, cacti and flowering plants. Generally the formulas are higher in nitrogen for foliage plants and higher in phosphorus for flowering plants.

Plant foods are also available for specific outdoor plants, such as roses and acid-loving plants like rhododendron. Spikes and tablets offer a clean, convenient way to feed, especially in containers where nutrients are leached out by watering.



Lawn Fertilizers

Lawns have specific fertilizer requirements, depending on the season and the type of turfgrass you grow. Read the instructions on the package carefully before purchasing. Lawn fertilizers containing various percentages of nitrogen, phosphorus and potassium are common lawn foods.

Starter fertilizers and winterizers provide extra phosphorus for root growth. Starter fertilizers are applied to provide a boost to newly seeded lawns. Winterizers are used as a last fall feeding to promote off-season root growth.

Another type of fertilizer, one combined with pesticides, is also widely used.



Weed and Feed and Pre- or Post-Emergents

Weed and Feed is a common term which refers to fertilizer that contains weed killer for broadleaf weeds, such as dandelions or grassy weeds like crabgrass. Look on the label for a list of weeds that can be treated with the product. The two types are:

  • Pre-emergents, such as those commonly used to prevent crabgrass, are weed killers that must be applied before the weeds germinate. They're ineffective if the weeds are already actively growing. Pre-emergent weed killers are often mixed with fertilizer and are applied early in the season.
  • Post-emergents are contact killers. They're effective only if the weeds are already actively growing. They won't kill weeds that haven't yet germinated.

The timing of application of pre- and post-emergents is critical for success. Applying these products too early or too late is essentially a waste of time. If sowing grass seed is also in your lawn schedule, make sure that there's a proper time interval between applying weed and feed and sowing. Read the package carefully before selecting to be sure which product fits your needs.



Organic Fertilizer Alternatives

Nonsynthetic organic fertilizers, soil conditioners and soil additives are also widely used. Because they lack some added ingredients to slow the nutrient release, these products may have to be applied more frequently. As with synthetic products, apply properly and with caution. Some of the most commonly used are:

  • Green Sand: from sedimentary marine deposits. Contains potassium and iron.
  • Blood Meal: a byproduct of the meat packing industry. Steamed and dried, it's high in phosphorous.
  • Compost: one of the best all-around garden materials for soil improvement.
  • Cottonseed Meal: a byproduct from cotton processing. This is a good source of nitrogen.
  • Fish Emulsion: a fish processing byproduct. Mild, nontoxic and organic, fish emulsion is good for use with tender plants that may suffer fertilizer burn. Yes, it does smell like fish.
  • Super Phosphate: rock phosphate combined with sulfuric acid to produce phosphorus in a form easy for plants to uptake.
  • Composted Manure: for soil conditioning or use in the compost pile.


Fertilizer Tips and Tricks

Just because the soil looks rich and dark doesn't mean that the nutrients are all there. Soil nutrients can become depleted over time and need a boost. A soil test is the key. The soil test tells you what's already there (so you don't add more) and what's missing. Lime is used for raising pH (making it more alkaline). Sulfur lowers soil pH (making it more acidic).

Apply Properly

Over-application of fertilizer is a common occurrence. Too much product applied faster than the plant can absorb it wastes fertilizer and harms the plant.

Always apply fertilizer at the proper time. Don't apply slow-release fertilizer late in the growing season. You don't want to boost foliage growth with nitrogen-heavy fertilizers prior to the dormant season. 

Crop Rotation and Intercropping

Each species of plant needs a different mix of nutrients. Rotation of plantings allows you to get the most from your garden soil.

Intercropping is the planting of different varieties within a close vicinity. Using principles of companion planting, intercropping lets plants' natural qualities complement each other.

Green Manure

Crops that are planted with the specific intended purpose of being worked back into the soil are known as green manure. These cover crops are chosen for their nutrient value and are used by serious home gardeners as well as commercial agricultural growers. 

Fertilizer Safety

Excess product from fertilized areas has to go somewhere. That somewhere is either down into the ground, affecting the water table or running off to affect nearby areas. That runoff could eventually end up in the water supply downstream.

Shop for Fertilizer

When using lawn treatments or lawn care products, always follow package directions regarding proper clothing, protective equipment, application procedures and safety precautions.

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