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What Do The Numbers On A Bag Of Fertilizer Mean?

Fertilizers have 3 numbers listed on their container known as N-P-K

N = Nitrogen which makes your plant grow and makes it greener.

P = Phosphorus makes it bloom, fruit and build good roots

K = Potassium heat and cold hardiness

Hang in there – we’re going to talk numbers, but I’ll keep it simple.  The NPK numbers tell you how much of each item is in the fertilizer.  Knowing what the NPK does will help you choose the fertilizer for your need.

General Lawn fertilizers – look for a larger 1st number.  (29-0-4)

To increase blooms or fruiting – look for a larger 2nd number (12-24-12)

For all purpose fertilizing – look for a balanced number (13-13-13)

For you Geeks, if you add up the numbers of the NPK it totals the amount of fertilizer in the bag.  For example, the total fertilizer in a bag of 13-13-13 equals 39.  So, 39% of the material in the bag is fertilizer and 61% is filler which helps in spreading the fertilizer.

Fillers can include sand, limestone, sawdust, clean or sterile dirt, peat moss, sphagnum, ground corn cobs or other similar fillers.

You may have noticed that organic fertilizers show much lower N-P-K numbers than a synthetic fertilizer.  By law, the ratio can only list nutrients that are immediately available to a plant. Many organic fertilizers contain slow-release nutrients that are available over time instead of immediately and therefore cannot be counted in the N-P-K numbers.  However, they will continue to fertilize a plant longer than a synthetic fertilizer. 



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