Understanding Fertilizer

hand with fertilizer pellets over seedling
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Understanding Fertilizer

Fertilizing Your Garden or Lawn Replaces Soil Nutrients and Amends Deficient Soil

Temperature, aeration, moisture and acidity are also very important, but if your soil lacks the nutrients that your plants need to grow, none of those things will matter.

In nature, the nutrients in the soil will be replenished over time. The leaves drop to the ground, the rain falls and the earthworms and bacteria in the soil get to work decomposing the materials and returning them to the earth as usable nutrients. It takes time to complete this process and it is an ongoing process. When people clean out our gardens, it’s ideal to have a compost pile where the garden debris will break down and then be returned to the earth. If gardeners are gardening much more intensively and even succession planting, this means the same soil may have to support more than one planting in one season. This can quickly deplete the soil of some or all the nutrients your plants need to grow. This is why adding plant fertilizer to the garden is so important.

There are two different types of fertilizers: synthetic and organic. Organic fertilizer comes from plants and animals, while synthetic fertilizer is made in a lab. Because synthetic fertilizer is manufactured, it can be much more concentrated. These are fertilizers that are labeled 10-10-10 or even 20-20-20. Organic fertilizer is usually much lower in concentrations like 2-2-2 or 1-2-3. These fertilizers are commonly referred to as gentle fertilizer.

Fertilizer Ingredients

Most commercial fertilizers contain three key ingredients: nitrogen (N), phosphorus (P) and potassium (K). Trace elements, such as iron, boron, chlorine, manganese, copper and zinc are important, too, but rarely need to be supplemented. They are often included in very small amounts, just in case. Other necessary elements such as carbon, hydrogen and oxygen are taken from the air and water, not from the soil. Nitrogen, phosphorus and potassium are the three ingredients represented by the numbers in the fertilizer name. For example, an all-purpose fertilizer might be called 10-10-10 because all three elements are present in equal proportions. When all the numbers are identical, the fertilizer is commonly referred to as a balanced fertilizer.

Nitrogen (N)

Nitrogen is most important for green growth. Later in the season, when your plants should be entering dormancy, green growth is unwanted and nitrogen intake should be reduced. Also, too much nitrogen will prevent blooms from developing. Nitrogen is water-soluble and moves through the soil very quickly. It must be replaced more often than the other elements unless you are using a slow-release fertilizer.

     Sources: All-purpose commercial fertilizer, urea from microorganisms in the soil, blood meal, manure, sewage leak (AKA that really green spot in the lawn over the septic tank)

Phosphorus (P)

This element promotes root growth, fruit ripening and seed development, and it is especially important for very young plants and right before plants go into dormancy for winter. Phosphorus naturally occurs in composting organic matter in the soil.

     Sources: All-purpose commercial fertilizer, earthworms, compost

Potassium (K)

Often called “potash,” this element is important for the development of fruit and leaves, and it is responsible for the overall health of the plant and disease prevention. Potassium controls the exchange of oxygen and carbon dioxide for the plant. Potassium is important in root development. The most obvious sign of deficiency is scorched leaves.

     Sources: All-purpose commercial fertilizer, wood ash, seaweed meal, compost, manure

When to Fertilize

The first step to a good fertilizer schedule is to have your soil tested. This will tell you if your soil is depleted of any or even all of the necessary nutrients. Soil testing is usually available through the local County Extension Office. You can also test the soil yourself with a home soil test kit you can purchase along with other garden supplies. By testing the soil, you will know exactly what your soil needs and, even more importantly, what it doesn’t need. It is just as important not to over-fertilize. You can choose the correct concentration of each element if you use the results of a soil test.

You may want to fertilize your seedlings if you start your own plants. These baby plants don’t need fertilizer in the same amounts as plants in the garden. Dilute the fertilizer by half if you choose to fertilize. If the recommended proportion is a tablespoon of fertilizer to a gallon of water, use a half tablespoon to a gallon of water.

Once your plants are in the garden, you may want to supplement certain crops with side dressings of fertilizer. Corn, for example, is a heavy nitrogen feeder. A side dressing of fertilizer high in nitrogen can be very beneficial.