Fertilizing 101

As most people are aware of, plant must have light, water and nutrients to grow.  For most people the sun with provide the light, the water will either come from the sky and/or by irrigation.  The nutrients found in the earth will be derived from compost, manure, fertilizers the hopefully the combination for the three.  If the plants are yielding well, fertilizing will help if that is the issue.  Remember plant can also be affected by water-logged soils, excessive shade or “pushed” out by larger plants such as a tree.

The fertilizer you obtain will either be organic – manure from poultry, cow, etc.) or inorganic – chemical, manmade products.

What to Purchase

Fertilizer bags should have three numbers listed on them, refereed to as the analysis.  This shows the percentage of nitrogen, phosphorus and potassium in contained within.  Luckily they are always listed in the same order.  Example: 10-13-15  would be 10 % Nitrogen, 13% Phosphorus and 15% Potassium.  The rest of the material is either a carrier or filler (sand, rice hulls etc.) A complete fertilizer will have all three elements included.

Nitrogen – used by the plant for growth, the roots, leaves, stems, flowers and fruits; providing plants their green color. Nitrogen deficiency causes yellow leaves and a pale green plant. Warning: too much will ‘burn’ and kill the plant

Phosphorus – used for cell division and helps form roots, flowers and fruit. Phosphorus deficiency causes stunted growth and poor flowering and fruiting.

Potassium – used for a variety of the chemical processes that are used for life and growth.  A shortage shows up in various ways, but stunted growth and yellowish lower leaves are common symptoms in many plants. 

The Selection

Most gardeners should use a complete fertilizer with twice as much phosphorus as nitrogen or potassium. Most of the time my soil has contained enough potassium and didn’t need more; and a slight excess of potassium will not injure the plants.  I found it easier to just get the complete fertilizer… Please don’t make the mistake I did when I started and used lawn fertilizers. It normally contains too much nitrogen, and can be mixed with chemicals for lawn weed control that will kill vegetables.

When testing your soil you get pH levels below 5.7 add lime. Lime adds calcium and makes it less acidic.


Test the soil every 2 years,  this is really important for beginning gardeners. A soil test clearly indicates the levels of nutrients in the soil and recommends the amounts of each nutrient to add. To collect a soil sample, select a time when the soil is moist but not wet. Dig down about 4 to 6 inches and take a handful of soil. Do this in several different places in the garden. Place each handful of soil in a large container and mix. Soil can be tested in midwinter to prepare for spring planting.

If the garden soil has not been tested, use 2 to 3 pounds of fertilizer such as 10-20- 10 for every 100 square feet of garden area. A plot 10 x 10 feet (or 5 x 20 feet) would be 100 square feet. If a garden is 30 feet long and the rows are 3 feet apart, each row is almost 100 square feet. Use 2 pounds of fertilizer if the garden is sandy and 3 pounds if the soil is mostly clay.   Two cups of most fertilizers will weigh about 1 pound. If a fertilizer has more nitrogen, use less. Two pounds of 5-10-5 fertilizer supplies as much nitrogen as 1 pound of 10-20-10.

If you are using organic fertilizer such as barnyard manure, spread it evenly over the garden and work it into the soil. Use 20 to 30 pounds of manure for every 100 square feet of garden. Do not use too much. Do not use fresh manure because it can injure plants. 

Applying the Fertilizer

Fertilizers can be applied the following ways:

  1. Broadcast before planting. The proper amount of fertilizer is spread evenly over the garden and mixed with the soil to a depth of 3 to 4 inches before rows are made. This method is the least likely to cause plant damage and usually is best for home gardeners.
  2. Band or row applications. The fertilizer is applied in a strip to the side of the row before planting. With this method you must be careful to prevent the roots from coming in contact with the fertilizer, which can kill plants.
  3. Starter solution. This is used only on transplants such as tomato, pepper, eggplant and cabbage. Mix 2 tablespoons of garden fertilizer in 1 gallon of water and stir well. Pour 1 cup of the mix into the hole and let it soak in before transplanting.
  4. Application to growing plants. This is especially helpful on sandy soils or when there has been a lot of rain that may have leached nutrients from the soil. Fertilizer is sprinkled along the sides of rows and watered into the soil (Fig. 5). About ½ cup of garden fertilizer for every 10 feet of row usually is enough. The amount and timing of fertilizer needed varies according to the type of vegetable planted. This will increase the yield of most vegetables. 


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