The Fertilizer Bag Label, Read Line by Line

Why this matters

Every rate you put down starts with a number read off a bag, and the bag is where most fertilizer mistakes are made before the spreader ever moves. A tech who reads "8.4% slowly available" as a share of the nitrogen will load a quick-release bag onto a route that needed slow release, and the burn or the runoff complaint arrives a week later. The label is short, regulated and laid out the same way on nearly every turf product, so learning to read it once pays every visit.

The label, as it arrives on the pallet

This is an illustrative mock of a straight turf fertilizer (no pesticide in it). The layout follows the model fertilizer label most states have adopted through their fertilizer control laws, so the lines sit in roughly this order on real bags.

   TURF FERTILIZER 24-0-6
   ------------------------------------------
   GUARANTEED ANALYSIS
   Total Nitrogen (N) ................ 24.0%
      1.6% Ammoniacal Nitrogen
     18.8% Urea Nitrogen
      3.6% Water Insoluble Nitrogen
   Available Phosphate (P2O5) ......... 0.0%
   Soluble Potash (K2O) ............... 6.0%
   Sulfur (S) ......................... 1.8%
      1.8% Combined Sulfur
   ------------------------------------------
   Contains 8.4% slowly available nitrogen
   from polymer-coated urea and methylene
   urea.
   Derived from: ammonium sulfate, urea,
   polymer-coated urea, methylene urea,
   muriate of potash.
   ------------------------------------------
   Covers up to 15,000 sq ft
   Net weight 50 lb (22.7 kg)
   Lot: 24B-118      Registrant name, address

Read it the way the state does: the guaranteed analysis is the promise, the slow-release line is a separate claim the registrant must back up, and the coverage line is marketing with a rate hidden inside it.

The grade is three guarantees, not a recipe

The three numbers are percent by weight. 24-0-6 means 24 lb of nitrogen, no phosphate and 6 lb of potash in every 100 lb of product. The other 70 lb per 100 is the rest of each molecule, coatings and carrier.

The second and third numbers are oxides. Phosphate is guaranteed as P2O5 and potash as K2O, a convention older than anyone working. To get elemental phosphorus multiply P2O5 by 0.44; to get elemental potassium multiply K2O by 0.83. You rarely need the elemental figure for turf work, but a soil test report sometimes gives phosphorus or potassium in elemental terms, and comparing a report in P with a bag in P2O5 without converting overstates the bag by more than double for phosphorus.

A zero in the middle is now the norm on maintenance turf products, because a number of states and localities restrict phosphorus on established lawns unless a soil test shows a need or the lawn is being seeded or sodded. Where that restriction applies, the middle number is the first thing you check, and a bag left on the truck from a seeding job can put a crew out of compliance on the next stop.

Reading the nitrogen breakdown

Under the Total Nitrogen line the label itemizes nitrogen by chemical form. Each line is a percent of the whole product, and the lines must add to the total: 1.6 plus 18.8 plus 3.6 is 24.0. If they do not add on a bag you are reading, you have misread a line or the label is in error, and either way you stop and check before the bag goes on a route.

Ammoniacal nitrogen is nitrogen as ammonium, here from ammonium sulfate. It is quickly available, it acidifies the soil slightly, and it is the source of the combined sulfur line (ammonium sulfate carries sulfur in the same molecule).

Nitrate nitrogen, when present, is the most mobile form. It moves with water through the root zone and is the form most likely to leach on sand. This bag has none, which is common on turf granules.

Urea nitrogen is the big line on most turf products, and it hides a split. Plain urea is quick: it converts to ammonium within days in warm moist soil, and on a hot surface it can lose nitrogen to the air as ammonia unless it is watered in. Labels for urea-heavy products usually direct watering in after application, commonly with a quarter to half inch of rain or irrigation; the label's own figure governs. Polymer-coated urea is also reported here, because chemically it is still urea; the coating only slows its release. So the urea line alone cannot tell you how fast this bag feeds. That is the job of the next line down.

Water insoluble nitrogen (WIN) is nitrogen that does not dissolve in cold water, here from methylene urea. Soil microbes release it over weeks, faster in warm soil and slower in cold. WIN is always slow, but slow nitrogen is not always WIN.

Other water soluble nitrogen, when listed, is usually the short-chain part of methylene urea or a similar reacted product. It sits between quick and slow, and labels that have it typically fold part of it into the slow-release claim.

Where slow release actually shows

The slow-release statement is a separate sentence under the guaranteed analysis: "Contains 8.4% slowly available nitrogen from polymer-coated urea and methylene urea." Three facts about it trip people up.

The 8.4 is a percent of the product, not a percent of the nitrogen. To get the share of the nitrogen that is slow, divide by total N: 8.4 divided by 24.0 is 0.35, so 35% of this bag's nitrogen is slow and 65% (15.6 points of the 24) is quick. Reading "8.4%" as "8.4% of the nitrogen" understates this bag's slow fraction badly, and reading a different bag's "16%" as "16% of the nitrogen" can overstate a weak one.

The statement names its sources. In this mock the 8.4 points are 3.6 of WIN from methylene urea plus 4.8 of polymer-coated urea sitting inside the 18.8 urea line. The label is not required to give you that split, but you can sometimes back it out when the WIN line and the statement differ, as here.

A product with no statement makes no slow-release claim. "Premium", "long lasting" or "feeds up to 8 weeks" on the front panel is not the statement. If an ordinance on your route requires a minimum slow-release share, only the statement line in the guaranteed analysis area counts as evidence, because it is the claim the registrant is answerable to the state for.

The coverage claim and the spreader settings

The coverage line ("Covers up to 15,000 sq ft") usually sits near the net weight, and the spreader setting chart sits with the directions, often on the back panel. Neither is in the guaranteed analysis, and neither is a guarantee.

The coverage line hides a nitrogen rate. 50 lb of product at 24% N is 12 lb of N (50 times 0.24). Spread over 15,000 sq ft, that is 12 divided by 15, or 0.8 lb of N per 1,000 sq ft. Check it the other way: 0.8 lb times 15 thousand-square-foot units is 12 lb. That one line tells you what single-application rate the registrant designed the bag around. If your program calls for 0.75 or 1.0 lb N per 1,000 sq ft on that visit, the bag's coverage figure is not your coverage figure, and the conversion to product per 1,000 sq ft belongs to 'How to Calculate Fertilizer Product From the Bag Analysis'.

"Up to" is a ceiling at that rate, not a promise for your lawn. Coverage is figured on turf area, and on this shelf turf area is measured turf with beds, house and hardscape subtracted (see 'How to Measure a Lawn for Treatment Square Footage').

The setting chart names specific spreaders and assumes a walking speed and a clean, undamaged impeller. A dial number off the bag is a starting point for calibration, never a rate. The shop standard is to check output by weight over a measured area; see 'How to Calibrate a Rotary Spreader by Weight Over a Measured Area'.

Worked example: three bags against one ordinance

A crew lead is loading for a route inside a town whose fertilizer ordinance (illustrative for this example; read your own) bans phosphorus on established turf without a soil test, and requires that at least 50% of the nitrogen in any application be slowly available during the summer months. Three bags are on the shelf.

Bag A: the mock above, 24-0-6, "Contains 8.4% slowly available nitrogen." Phosphate 0.0%, so it passes the phosphorus rule. Slow share: 8.4 divided by 24.0 is 35%. Under 50%, so it fails the slow-release rule.

Bag B: 32-0-4, "Contains 16.0% slowly available nitrogen." Phosphate 0.0%, passes. Slow share: 16.0 divided by 32.0 is 50%. The rule says at least 50%, so it passes, right on the line. Read as nitrogen shares, "8.4" and "16" would have failed both bags.

Bag C: 18-24-12 starter, "Contains 6.0% slowly available nitrogen." Phosphate 24%. It fails the phosphorus rule on established turf before you look at nitrogen. Its slow share (6.0 divided by 18.0, or 33%) would fail too. This is the bag left over from last week's seeding job, and it is the one most likely to end up in the hopper by habit.

The crew lead loads Bag B and writes the lot number and the slow share (50%) on the route sheet. The rate for the visit still has to be computed from Bag B's 32% total N, which is a different product weight per 1,000 sq ft than Bag A would have needed, and the spreader setting from Bag A's last calibration does not carry over, because Bag B's granule size and density are different.

What would change the answer. Outside the summer window in this ordinance, Bag A passes. In a jurisdiction with no slow-release rule, Bag A is a normal maintenance product and the choice is agronomic, not legal. On a newly seeded lawn, Bag C may be the correct product, and many phosphorus restrictions carve out establishment, but the carve-out is the ordinance's to define, not yours. See 'The Fertilizer Ordinance Check Before Application SOP'.

What a label will not tell you

It will not tell you how much of each source is in the bag. The derived-from line lists ingredients, not proportions. Do not try to infer the slow share from the order of the ingredients.

It will not set a legal application rate for a straight fertilizer the way a pesticide label does. For straight fertilizer the limits come from your state and local ordinance (blackout periods, setbacks from water, per-application nitrogen caps). If the bag also carries a weed control or insect control ingredient, it will carry an EPA registration number, and then it is a pesticide product: the label's directions are law under FIFRA, the applicator licensing rules apply, and every rate and site comes from that label. See 'Pesticide Label Reading and Compliance'.

It will not tell you the bag's age or how it was stored. A polymer-coated product that sat wet and caked in a trailer can release faster than its statement suggests, and a caked bag does not meter through a spreader the way calibration assumed. Torn, wet or caked bags get set aside.

It will not tell you what the soil needs. Potash, sulfur and phosphate decisions come from a soil test, not the grade on whatever is on the shelf. See 'Soil Test Collection and Interpretation'.

Keep the lot number. It is the only line that ties a burn complaint or a product recall to what went down on a specific lawn, and it costs a few seconds to write on the application record.

References

• AAPFCO (Association of American Plant Food Control Officials) Official Publication, the model fertilizer bill and labeling rules, in the form your state has adopted into its fertilizer control law; check your state department of agriculture for the current version
• Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), for fertilizer products that also contain a pesticide; the product label governs
• Your state and local fertilizer ordinance (phosphorus restrictions, blackout periods, slow-release requirements)
• See related: How to Calculate Fertilizer Product From the Bag Analysis; How to Calibrate a Rotary Spreader by Weight Over a Measured Area; Fertilizer Math by N-P-K
• See related: Pesticide Label Reading and Compliance; Soil Test Collection and Interpretation