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All About Fertilizing

Feeding Your Plants

For a plant, the idea of a great meal is not a burger, fries and soft drink. For them it's more like a complete balanced mix of three main nutrients: nitrogen, phosphorous and potassium. These are sold as fertilizers.

Almost all gardens need to have fertilizer added to them. It helps to replace the nutrients that plants use and keeps your soil in good shape for future crops.


How do these nutrients help plants? Well, let's take a look.

Nitrogen is used by plants for lots of leaf growth and good green color.

Phosphorous is used by plants to help form new roots, make seeds, fruit and flowers. It's also used by plants to help fight disease.

Potassium helps plants make strong stems and keep growing fast. It's also used to help fight disease.

Fertilizer is one of the many garden "tools" that is used in making good gardens great gardens.

All fertilizers have three numbers on the label which indicate the fertilizer analysis, or "percentage by weight" of nitrogen, phosphorus and potassium, in that order.
Therefore, a 50 pound bag of fertilizer labeled 20-10-5 would contain 20% nitrogen (10 pounds), 10% available phosphates (5 pounds), and 5% soluble potash (2.5 pounds). 
See the calculations below:

50 pound bag of 20-10-5 fertilizer:
  20% nitrogen (.20 x 50 lbs = 10 lbs)
  10% available phosphates (.10 x 50 lbs = 5 lbs)
    5% water soluble potash (.05 x 50 lbs = 2.5 lbs)

Furthermore, this product would be considered a "complete" fertilizer, since all three nutrients are present.
An "incomplete" fertilizer would have a label like 0-0-60 or 46-0-0, since it would only have one of the three major nutrients present. Another example of an incomplete fertilizer would be 0-20-20, since one of the three nutrients is missing.  Fertilizers also have "ratios" which indicate the relative amounts of nutrients to each other. For example, a 10-10-10 fertilizer is a 1-1-1 ratio, and a 20-10-5 fertilizer is a 4-2-1 ratio.  Ratios can be helpful when looking for the "right mix" for a certain type of plant or situation.  For example, vegetable gardens often call for a 1-2-1 ratio, which would translate into a 5-10-5 or 10-20-10 fertilizer.  Most trees like a 2-1-1 ratio, which would be a fertilizer product such as 10-5-5 or 20-10-10.  Lawns prefer a 3-1-2 ratio fertilizer, so a fertilizer product with 30-10-20 on the label would be a good ratio match.
High analysis fertilizers (those with larger numbers on the label) would be applied at a lower rate to yield the same results.  In other words, 5 lbs of a 20-20-20 fertilizer would yield the same amount of actual nutrients as 10 lbs of a 10-10-10 fertilizer.


NITROGEN:  Promotes vigorous blade, leaf and stem growth. Encourages dark green color. Assists in chlorophyll production. Improves overall plant health, quality, and density. Aids in tolerance to heat, cold, and drought stress.

PHOSPHORUS:  Promotes early plant development Hastens plant maturity. Promotes bloom and root development.

POTASSIUM:  Improves tolerance to drought, disease and heat Increases winter hardiness. Aids in water uptake. Enhances overall health and vigor.


Just because fertilizer is in the soil doesn't mean that the plant is able to use it. When a soil's pH is too low (below 6.0) or too high (above 7.0), it can severely limit the plants ability to take in the fertilizers nutrients. Lime is the most effective soil treatment to correct the low pH problem that is predominant in Atlanta's red clay soil. Forty pounds of lime per 1000 square feet annually is generally recommended.