Here's a list of some organic fertilizers you can encounter:

Manures for the garden come from cow, sheep, poultry and horses. Pretty self-explanatory. Manure is known as a "complete" fertilizer; it has a lot of organic matter, but is low in nutrients. Manures are most valuable as organic soil amendments and mulches. Note: Beware of using fresh manure as a fertilizer because it can burn plants.

Bat guano is protected by caves from leaching, so nutrients are conserved. It is rich in soluble nitrogen, phosphorous and trace elements. Usually powdery, bat guano may be used any time of year as a top dressing or diluted in a tea and used as a foliar spray.

South American seabird guano is among the world's best. It is gathered off the rocks of arid sea islands, where rainfall and decomposition is minimal. As a result, seabird guano is very high in nitrogen, phosphorous and other nutrients. At Planet Natural, we offer all kinds of garden supplies, including guanos, which provide plant nutrients in a natural form.

Bone meal is finely ground bone. A by-product from animal slaughterhouses, it is a great source of calcium and contains up to 15% phosphate. Bone meal promotes strong root systems and flowering. It is often used when growing flowers, bulbs and fruit trees.

Shellfish fertilizer or shell meal is made from crushed bones or shells from crab or other shellfish. It is a great source of calcium in addition to phosphorus and many trace minerals. One benefit of shellfish fertilizer: it contains chitin which encourages the growth of organisms that inhibit harmful pest nematodes.

Blood meal is dried, powdered blood collected from cattle slaughterhouses. It's such a rich source of nitrogen that gardeners have to be careful not to over-apply and burn the roots of their plants. Apply just before planting to stimulate green leafy growth.

Rock phosphate is a calcium or lime-based phosphate rock that is usually ground to the consistency of small crumbs. This rock powder contains over 30% phosphate and a large number of trace elements. Rock phosphate does not leach out of the soil, remaining unchanged until taken up by the roots.

Greensand is an iron potassium silicate that gives the minerals in which it occurs a green tint. Mined from an ancient New Jersey sea bed deposit of shells, it is rich in iron, potassium and numerous micronutrients.

Fish emulsion is a partially decomposed blend of finely pulverized fish. It can smell, although some deodorized versions have been developed. Like blood meal, it should be used sparingly in order not to burn plant roots.

Sewer sludge are the solids that remain after sewage treatment. The treated sewage is inoculated with microorganisms and aerated. Then it is filtered, dried, ground, and screened. It is often used as both a soil amendment and a fertilizer on ornamentals and lawns. Note: Sludge is no longer allowed for use in organic crop production due to concerns about heavy metals.

If all of those are organic fertilizer, you're probably wondering what makes for an inorganic fertilizer. Non-organic fertilizers are synthetic chemicals.

Organic Fertilizers vs. Inorganic
There are advantages and disadvantages to organic and inorganic fertilizers. The major benefit of organic fertilizers is that they work slowly. They need to be broken down by soil organisms in order for their nutrients to be released and that takes time. Because they work slowly, nothing is wasted. They are consumed as they are released, unlike chemical fertilizers, which are released immediately into the soil.

Organic fertilizers carry some other perks. Because they contain organic material, they improve the soil's structure or its "workability." Soil that's been fertilized with organic matter is easier to work and allows more air to get to plant roots. The organic material also permits soil to hold water longer. Finally, the addition of organic substances used in fertilizer increases the bacterial and fungal activity in the soil. Overall, organic fertilizer not only helps your plants, it improves your soil.

Organic fertilizers' biggest strengths are also their weakness. Because organic fertilizer's nutrients are slowly released into the soil, they are not immediately available to plants. If there is an immediate need for nutrients, you may want to consider liquid fertilizers or foliar applications.

Inorganic fertilizers work fast, which can be a boon or a bane depending on your garden's needs. Another disadvantage of inorganic fertilizer is that over watering or rain can push the chemicals beneath roots where they won't do any good. Inorganic fertilizers, because they are so rich, can easily "burn" roots or create a toxic concentration of salts if over-applied.

Although organic fertilizers do carry many benefits, especially over time, plants often do not know the difference. Your zucchini plant doesn't care if the nitrogen it's feeding on came from a compost pile or a test tube.

Proper Use

To ensure proper use, first figure out what your plants' nutrient needs are. This is based on soil conditions, previous fertilizers used and the type of plants that you are growing. The best way to find out what you need to add to the soil is to test and determine what's in your soil. A soil test can cost anywhere from $10 to $40 per sample and should be done every two to three years. (Any time you encounter problems is also a good time to have the soil retested.) At Planet Natural we offer a simple, yet accurate soil test kit that uses a "color comparator" and capsule system for under $20.00.

A soil test report will present findings such as the pH being "normal," the amount of iron being "adequate" and the amount of potassium being low. It will include nutrient recommendations for material that needs to be added. For example, if the report says your soil is low on potassium, it will recommend that you add two pounds of potassium per 1,000 square feet.

Also, know the labeling system that the industry has standardized on. Each label will list N-P-K numbers and in that order. The N stands for nitrogen, the P for phosphorus and the K for potassium. An organic fertilizer will generally have an NPK ratio that adds up to less than 15 and with no individual number greater than thirteen. If you see big numbers on the label, chances are it's chemical rather than organic. A "6-12-0" fertilizer contains 6 percent nitrogen, 12 percent phosphate and 0 percent potash. A hundred pound bag of this material would contain six pounds of nitrogen (100 x .96), 12 pounds of phosphate (11 x .12) and no potash.

Lower numbers do not mean low grade. In the case of organic fertilizers it just means that the nutrients aren't immediately available, but are released slowly over time. Note: It is our opinion that some fertilizer companies use high NPK ratios purely for marketing purposes. The "more must be better" philosophy is alive and well in the industry...but does a lawn really require a fertilizer that consists of 60% nitrogen?

Fertilizers with ingredient lines that include words like ammonium, muriate, urea, nitrate, phosphoric, or super phosphate usually are chemical-based rather than an organic fertilizer.

Also be wary of fertilizers that contain cottonseed meal and leather tankage. These aren't bad in and of themselves, but they are frequently contaminated with harmful residues.

Using Fertilizers

Whatever fertilizer you buy, follow the application instructions including how much to apply, when and where.

When using organic fertilizers, which are mostly slow-release materials, the timing of fertilizing is not as critical as it is when using fast-release chemical fertilizers. Plan to work fertilizers into garden beds every spring as soon as the soil can be worked. Highly productive plants, including vegetables, should have regular monthly applications of organic fertilizer.

Proper use of organic fertilizers can give you a bumper crop of vegetables or flowers that will be the envy of your neighbors.