A Crash Course in Fertilizers: NPK Ratios, Synthetic vs. ...

Learn the basics of fertilizers, and you’ll help your garden grow as never before!

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Fertilizer sections at nurseries, garden centers, and supply stores dazzle the gardener. The shelves are piled with boxes and bottles, the floors covered with bags stacked high. Labels identify the package contents as organic compost, rose food or vegetable food, lawn fertilizer or general-purpose fertilizer. In some stores, you’ll find bins filled with bone meal, blood meal, or hoof-and-horn meal―all labeled natural fertilizer. Choosing the right products to keep your plants healthy can often be a bit confusing.

Regardless of its type, any fertilizer you buy will come with information about the nutrients it contains, so you want to understand the N-P-K-ratio.

Prominently featured, the N-P-K-ratio is the percentage the product contains by volume of nitrogen (chemical symbol N), phosphorus (P), and potassium (K). A 16-16-16 fertilizer, for example, contains 16% nitrogen, 16% phosphorus, and 16% potassium. A 25-4-2 formulation contains 25% nitrogen, 4% phosphorus, and 2% potassium.

All fertilizers contain at least one of these components; if any is missing, the ratio will show a zero for that nutrient. (A 12-0-0 fertilizer contains nitrogen but no phosphorus or potassium, for instance).

Boxed, bagged, and bottled products display the N-P-K ratio on the label. For fertilizers sold in bulk from self-serve bins, the ratio is noted on the bin. One tip: Be sure to write the information on the bags you fill before you bring them home.

Complete and Incomplete Fertilizers

A fertilizer containing all three major nutrients is called a complete fertilizer; a product that supplies only one or two of them is an incomplete fertilizer.

Using a complete fertilizer for every garden purpose seems sensible, but, in fact, it isn’t always the best choice. If the soil contains sufficient phosphorus and potassium and is deficient only in nitrogen (as is often the case), you can save money by using an incomplete fertilizer that provides nitrogen alone (ammonium sulfate, for example). In some instances, complete fertilizers can even harm a plant. Exotic, bright-blossomed proteas, for example, will not tolerate excess phosphorus: they “glut” themselves on it and then die.

The inexpensive soil test kits sold at garden centers can give you a rough idea of the nutrients available in various parts of your garden. For a more detailed evaluation, you may want to pay for professional analysis, and there are mail-in versions of soil test kits, too. By revealing which nutrients may be lacking, testing can help you choose an appropriate fertilizer.

Kyle Johnson

General and Special-Purpose Fertilizers

The various products labeled “general-purpose fertilizers” contain either equal amounts of each major nutrient (N-P-K ratio 12-12-12, for example) or a slightly higher percentage of nitrogen than of phosphorus and potassium (such as a 12-8-6 product). Such fertilizers are intended to meet most plants’ general requirements throughout the growing season.

Special-purpose fertilizers, on the other hand, are formulated for specific needs. They’re aimed at the gardener who wants a particular combination of nitrogen, phosphorus, and potassium for certain plants or garden situations. These fertilizers are of three general types.

One type, used during the period of active growth, contains largely nitrogen. Such products, with N-P-K ratios such as 16-6-4, are often used in spring, when you want to encourage lush growth or green up your lawn.

Another type is meant to stimulate root growth, stem vigor, and flower and fruit production. Fertilizers of this sort contain little nitrogen and higher levels of phosphorus and potassium; the N-P-K ratio may be 3-20-20, for example. These products are applied at different times and in different ways, depending on what you want to achieve. When you prepare a new planting area, for instance, you’ll work a dry granular fertilizer of this sort deeply into the soil, putting the phosphorus and potassium where roots can absorb them. The nutrients help strengthen the new plants’ developing stems and encourage the growth of a dense network of roots.

To promote flower production and increase the yields of fruit or vegetable crops, you apply the same sort of fertilizer to established plants after they’ve completed their first flush of growth. You can use either dry granules, scratching them lightly into the soil, or apply a liquid formula with a watering can or a hose-end applicator.

Courtesy of Urban Farmstead

A third group of fertilizers is designed for use on specific plants. These feature the N-P-K ratios determined to elicit the best performance from the particular plant, as well as other elements proven valuable to that plant. Such fertilizers are named according to the plant they’re intended to nourish. Especially useful are formulas for citrus trees and acid-loving plants such as camellia and rhododendron.

Recently, other such plant-specific fertilizers have appeared on nursery shelves, each claiming to be the best choice for a certain plant or group of plants; you may see several sorts of “tomato food” or “flower fertilizer,” for example. The jury is still out on the benefit of many of these products, and you will often do just as well to use a general-purpose type. The main distinction is often the price: the “special” formulas are usually costlier than general-purpose kinds.

Organic Fertilizers

Organic fertilizers are derived from the remains of living organisms; blood meal, bone meal, cottonseed meal, and fish emulsion are just a few of the many available types. Organic fertilizers release their nutrients slowly: rather than dissolving in water, they’re broken down by bacteria in the soil, providing nutrients as they decompose.

One of the many benefits of organics is they improve the “structure” of the soil the microorganisms that convert nutrients so plants can access them. Micronutrients are also often present, but they are not in synthetics.

Because these fertilizers act slowly, it’s almost impossible to “burn” or kill lawns or plants by applying too much (overdosing with synthetics, in contrast, can have potentially fatal results). Some manufacturers combine a variety of organic products in one package, then offer them for general-purpose or specialized use. Finally, they aren’t as water-soluble as synthetics, which means they won’t leach into waterways.

Two commonly used soil amendments―compost and manure―have some nutritive value and can be used as part of an organic fertilizing program. The N-P-K ratio of compost varies from 1.5-.5-1 to 3.5-1-2. Chicken manure’s N-P-K ratio ranges from 3-2.5-1.5 to 6-4-3; that of steer manure is usually a little less than 1-1-1.

Fertilizers containing seaweed are gaining favor with many gardeners. Besides providing nutrients in a form immediately available to plants, seaweed contains mannitol, a compound that enhances absorption of nutrients already in the soil, and various hormones that stimulate plant growth. And the carbohydrates in seaweed break down rapidly, nourishing soil-dwelling bacteria that fix nitrogen and make it available to plant roots.

Mixed with water and sprayed directly on foliage, seaweed-containing fertilizers can have dramatic effects in a matter of days. Plants green up and begin to produce new growth, and those that are weak stemmed and straggly straighten up and become stronger.

Synthetic fertilizers

These products are derived from the chemical sources listed on the product label. They’re faster acting than organic kinds and provide nutrients to plants quickly, making them a good choice for aiding plants in severe distress from nutrient deficiencies, but they are more likely to “burn” the plant.

Synthetic fertilizers are sold both as dry granules to be applied to the soil and as dry or liquid concentrates to be diluted in water before application. In dry form, they’re usually less expensive than their organic counterparts. In some of the dry granular types (those known as controlled-release fertilizers), the fertilizer granules are coated with a permeable substance; with each watering, a bit of fertilizer diffuses through the coating and into the soil. Depending on the particular product, the nutrient release may last anywhere from 3 to 8 months.

Rachel Weill

Some synthetic products are packaged for special purposes; you’ll find spikes and tabs for container plants, for example.

Note that synthetic fertilizers usually do not contain any of the secondary or micronutrients mentioned above―but in most cases, these nutrients are already present in the soil. If a test indicates that some are missing, look for a fertilizer that provides them.

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Chicken manure, also known as "black gold," is one of the best nutrient boosts you can give your soil. But not all chicken manure is created equal. You can buy bags of organic chicken manure at a garden center. Or, if you have neighbors who raise chickens organically, ask them for some of the manure. Here’s the scoop on why chicken manure is so good for soil and how to choose the best kind.

What Is Chicken Manure?

If you want to learn more, please visit our website chicken manure npk 4-2-2.

Also referred to as poultry manure, chicken manure is an excellent source of nutrients. Its nitrogen and phosphorus content is at least twice as high as other farm manures such as cow manure. 

In addition to chicken droppings, chicken manure contains everything else that gets wiped up when a chicken coop is cleaned out, including urine, feathers, leftover feed, and coop bedding material such as straw and hay, pine or cedar shavings, grass clippings, shredded leaves, and recycled paper. That’s why the NPK ratio in chicken manure varies greatly. 

The percentage of chicken feces and other materials is not the only variable in the nutrient content. The age of the chickens and the way the chickens are raised also play a role.

The Benefits of Chicken Manure

As a non-synthetic organic fertilizer, chicken manure has numerous benefits.

• Nutrients: It is a complete fertilizer that contains the macronutrients nitrogen, phosphorus, and potassium, as well as important micronutrients such as calcium needed for healthy plant growth.
• Soil amendment: Chicken manure is more than a fertilizer though. It is also a good soil amendment; it adds organic matter to the soil, which improves soil structure, moisture-holding, drainage capability, and aeration. Also, soil high in organic matter is less prone to erosion and retains fertilizer better.
• Microbe food: The organic matter in chicken manure has another benefit: it feeds soil microbes and allows organic nutrients to break down faster, making them available to plants more quickly. 

Kondor83 / Getty Images

The Difference Between Bagged and Fresh Manure

Chicken manure comes in two types: commercially processed in bags or fresh and there are substantial differences in how to prepare and use them.

The bags you can buy at your local garden center are dried and pulverized or pelletized chicken manure. On a weight-for-weight basis, dried manure is more concentrated than fresh manure, which contains up to 76 percent water. Dried manure has usually been sterilized and it’s odor-free. 

Fresh manure from a backyard chicken coop or a farm has a strong smell and may contain harmful pathogens such as E. coli or Salmonella. Unlike dried manure, it cannot be used as such but must be composted or aged before it is applied, or else the high ammonia content will burn the plants. 

Tip

Chicken manure from conventionally raised chickens could be contaminated with antibiotics. There is little research available about the amount of residue from antibiotics in aged chicken manure. Using only organic chicken manure is the safer option.

How to Age Chicken Manure

Aging fresh manure will destroy harmful pathogens and reduce its ammonia content. The pathogens in the manure stop reproducing at temperatures of 140 to 160 degrees Fahrenheit. This is the temperature that can be reached in a compost pile, a common method of aging manure. Here's what to do:

1. Turn the compost pile with the fresh chicken manure weekly to introduce oxygen and shield it from the elements, as rain or snow will reintroduce more moisture.
2. Keep the compost pile with manure far away from your garden and other areas of your yard with human traffic, such as children’s play areas, to prevent contamination from the runoff. 
3. Check the compost pile after five to six weeks. The resulting aged manure is more compact, drier, and lighter. The nutrients in it have been stabilized so they will be slowly released once you add the aged manure to your garden soil. 

Applying compost mixed with aged manure

Grace Cary / Getty Images

How and When to Apply Chicken Manure

Processed manure in bags is applied differently from composted aged manure. However, when applying any type of chicken manure, work it into the soil evenly and always wear gloves when handling manure.

Bagged Chicken Manure

Apply bagged chicken manure at any time. Trees and shrubs are usually fertilized in spring. Flower beds and vegetables are fertilized in the spring and repeatedly throughout the growing season. For specific amounts, follow the instructions on the label. 

Aged Chicken Manure

If using composted aged manure, the timing for application is restricted depending on whether your crops are staked or not. Consider the expected harvest date of your crop and count backward to arrive at the application period. Usually, this translates into a late winter or early spring application for most locations. Here's how to apply aged manure:

• For trellised or staked crops where the fruit has no contact with the soil, such as tomatoes or beans, the manure needs to be applied at least 90 days before harvest.
• For crops that have contact with the soil—all root vegetables, strawberries, and leafy vegetables—the manure must be applied at least 120 days before harvest.
• Apply 45 pounds of aged manure per 100 square feet. 

FAQ

• What plants grow best in chicken manure?

  Nitrogen-loving plants and vegetables grow best in chicken manure. Consider using chicken manure to grow types of tomatoes, peppers, eggplants, squash, melons, strawberries, cucumbers, beans, and some fruit trees, such as apple trees, that prefer less acidic soil. Always research your specific crop for the amount of suggested chicken manure.

• What plants do not like to grow in chicken manure?

  Chicken manure is more alkaline than acidic so serious acid-loving plants don't like to grow in chicken manure. For example, plants such as blueberries, azaleas, and rhododendrons do not like to grow in chicken manure.

• What are some of the disadvantages of using chicken manure in a garden?

  There are disadvantages to using fresh chicken manure if it is not aged properly. It can burn the plants or introduce harmful pathogens into the soil. Bagged chicken manure does not have these problems if you follow the package's directions.

  Want more information on tsp fertilizer? Feel free to contact us.