Example: 2:3:4 (30)

Answer: N - P - K and (percentage of plant nutrition concentration)

What does this mean?

From this you can work out the concentration of the N, P and K. You do this by adding up the 3 numbers 2+3+4=9. You then take the number representing the N, P and K and divide that by the total. For example:
Concentration of N: 2/9 x 30 = 6.7% or 67g of N in a kg
Concentration of P: 3/9 x 30 = 10% or 100g of P in a kg
Concentration of K: 4/9 x 30 = 13.3% or 133g K in a kg

So, if you go back to the beginning and you had 2:3:4 (30) it would mean that you had 300grams of active fertilizer in a kilogram. If you look at the above working and add the grams you will see that it equals 300 grams. The remaining 700 grams is filler which if often lime chips which is also essential for the soil.

These are the "major nutrients"
Nitrogen - Phosphorus - Potassium

Nitrogen (N)

The Nitrogen percentage is the first number on the label

Example: 2-3-4 (30)

Nitrogen is a primary nutrient that really makes plants "grow."  When you put fertilizer on your lawn, most of the "green-up and grow" comes from the 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.

Nitrogen produces vegetative growth in plants, but too much nitrogen can cause problems.  One problem is succulent growth, which makes a plant more susceptible to certain diseases.

78% of our atmosphere is nitrogen, and rain and snow account for 2 to 12 pounds of actual nitrogen per acre (43,560 square feet), per year.  "Lightning charged rain" is high in NH4 and NO3.  Snow has been called "poor man's manure". . . now you know why!

Plants in the Legume family "fix" atmospheric nitrogen into the soil. Peas, beans, clover, and alfalfa are legumes, as well as Black Locust trees.

Fertilizer
Fertilizer

Phosphorus (P)

The Phosphorus percentage is the middle number on the label

Example: 2-3-4 (30)

Phosphorus is a primary nutrient that encourages rooting, blooming and fruit production in plants.

Vegetable gardeners have typically been told to apply 2-3-2 since the higher middle number (P) helps vegetable production.

Phosphorus is important for root-growth and blooming in plants, and is the main ingredient in "starter fertilizers" as well as liquid fertilizer "bloom boosters".

Phosphorus is lacking in most soils we have tested since 1979.  Applications of super-phosphate (0-20-0), triple super-phosphate (0-46-0), or bone meal (organic source) can be used to correct deficiencies.

Since phosphorus moves very slowly through the soil, it should be incorporated into the soil prior to, or during planting.  In existing lawns, we recommend core-aeration prior to phosphorus application.

Potassium (K)

The Potassium percentage is last on the label

Example: 2-3-4 (30)

Potassium helps plants resist disease and aids in winter hardiness. ("K" is the symbol for "kalium" or potash, and is commonly used to represent potassium)

Most 'winterizer' fertilizers used on lawns in late fall are high in Potassium, since it promotes winter hardiness in turf grasses.

Potassium fertilizers have a high "salt index" and should be used with caution, since they can "burn" plant foliage.

Most "complete" fertilizers contain potassium since it is fairly mobile, and readily leaches out of the soil profile.

Fertilizer
Symbol of Growth