Some gardening knowledge is gained by doing, other knowledge is gained by study. Fertilizers fall into the second category. But once you understand the basics of fertilizers and fertilization, it will all become rather simple. This page shares my knowledge about plant nutrients. Here's to vigorous plants through proper fertilization! Bob
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
This fertilizer would be considered a "complete" fertilizer, since all three nutrients are present.
An "incomplete" fertilizer might 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 (nitrogen) 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.
ALWAYS READ AND FOLLOW LABEL DIRECTIONS!
NITROGEN (N) - the Nitrogen percentage is the first number on the label. Example: 10-10-10
Nitrogen is a primary nutrient that makes plants "grow." When you put fertilizer on your lawn, most of the "green up and grow" comes from nitrogen.
QUICK RELEASE v. SLOW RELEASE NITROGEN
There are 'quick release' and 'slow release' forms of nitrogen. Slow release forms are more expensive but remain effective for a longer period of time. Organic fertilizers are slow release and have less potential to "burn" plants.
PHOSPHORUS (P) - the Phosphorus percentage is the middle number on the label. Example: 10-10-10
Phosphorus is a primary nutrient that encourages rooting, blooming and fruit production in plants. Vegetable gardeners have typically been told to apply 5-10-5 since the higher middle number (P) helps vegetable production.
NOTE: Many states have now limited or banned the use of phosphorus fertilizers due to pollution concerns of waterways.
POTASSIUM (K) - the Potassium percentage is last on the label and easy to remember since Potash is on the "ash end." Example: 10-10-10
Potassium helps plants resist disease problems and aids in winter hardiness. ("K" is the symbol for "kalium" or potash, and is commonly used to represent potassium)
SECONDARY NUTRIENTS: Ca - Mg - S
Secondary nutrients also play an important role in plant growth. The 3 secondary nutrients are Calcium (Ca), Magnesium (Mg) and Sulfur (S).
ESSENTIAL ELEMENTS: C - H - O
The essential elements are basic to plant growth, and need to be mentioned here, even though they aren't commercially available fertilizers. The 3 essential elements are Carbon (C), Hydrogen (H) and Oxygen (O). Plants obtain these elements from carbon dioxide (CO2) and water (H2O).
MACRONUTRIENTS: C - H - O N - P - K Ca - Mg - S
When you group the essential elements with the major nutrients and secondary nutrients, you end up with the 9 macronutrients: Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Potassium, Calcium, Magnesium, and Sulfur.
MINOR ELEMENTS: Fe - B - Mn - Cu - Cl - Mo - Zn
Nutrients needed by plants in lesser amounts are known as the minor elements. These include Iron (Fe), Boron (B), Manganese (Mn), Copper (Cu), Chlorine (Cl), Molybdenum (Mo), and Zinc (Zn).
How can you possibly remember everything?
Simple . . . start with the name and moniker of a famous restaurant manager used below:
C Hopkins, Cafe Mgr.
But mother's cooking is more zestful
C - Carbon
H - Hydrogen
O - Oxygen
P - Phosphorus
K - Potassium
I - (nothing)
N - Nitrogen
S - Sulfur
Ca - Calcium
Fe - Iron
Mgr - Magnesium
but - Boron
mother's - Manganese
cooking - Copper/Chlorine
is more - Molybdenum
zestful - Zinc