Fertilizers & Soil Amendments
Quick Answer
Fertiliser is sold by bag weight and applied by nutrient, and confusing the two is the most common costly mistake in lawn care. What matters is actual nitrogen per 1,000 square feet, which is the first N-P-K number as a percentage of the bag — a 20-0-5 bag is a fifth nitrogen, so five pounds of product carries one pound of nitrogen.
Before any of this is worth spending money on: a soil test. It is the only way to know whether phosphorus or lime is needed at all, and in some states applying phosphorus without one is restricted by law.
Which Type Do You Need?
- Established lawn, routine feeding → all-season fertilizers
- Seeding or overseeding → starter fertilizers
- Cool-season lawn in autumn → fall & winterizer
- You want slow, soil-building feeding → organic fertilizers
- You have never tested the soil → soil test kits — start here
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The Types, Briefly
All-Season Fertilizers
General-purpose feeding through the growing season.
Starter Fertilizers
Higher phosphorus for root establishment on new seed — where a soil test supports it.
Fall & Winterizer
The most important application of the year on cool-season lawns.
Organic Fertilizers
Slower release, more product by weight, soil biology benefits.
Liquid Fertilizers
Fast uptake, short duration. Useful for correction rather than as a programme.
Lime & Gypsum
pH and structure amendments. Only apply against a soil test result.
Iron Supplements
Colour without growth. Useful when you want green but not more mowing.
Soil Test Kits
The cheapest purchase in this category and the one that determines the rest.
How to Choose a Lawn Fertilizer
Work out the actual nitrogen before comparing anything else. Divide 100 by the first N-P-K number to get the pounds of product needed per pound of nitrogen — so a 24-0-6 bag needs roughly 4.2 pounds to deliver one pound of nitrogen per 1,000 square feet. Two bags with very different prices often deliver nitrogen at almost the same cost once you do this, and the cheaper-looking one is frequently the more expensive. After that, the decision is release rate: quick-release greens fast and risks burn and flush growth, slow-release feeds steadily and is far more forgiving of a calibration error.
| Specification | Why it matters |
|---|---|
| N-P-K analysis | The three numbers are percentages by weight. The first one, nitrogen, drives growth and colour and is what most programmes are built around. |
| Actual nitrogen per bag | The number that lets you compare products honestly, and the basis of every extension application rate. |
| Release rate | Slow or controlled release is more forgiving and reduces burn and leaching risk. Quick-release acts fast and punishes over-application. |
| Phosphorus (the middle number) | Frequently unnecessary on established lawns and legally restricted in several states without a soil test showing a deficiency. |
| Coverage area | Stated for a specific rate. Check which rate, because coverage claims assume an application rate you may not be using. |
| Weed-and-feed combinations | Convenient and usually a compromise — the right time to feed and the right time to treat weeds are rarely the same week. |
Swipe the table sideways to see every column.
What to ignore
- — Bag weight as a measure of value — it is nitrogen you are buying, not product
- — Micronutrient lists on bags where no deficiency has been established
- — Seasonal branding that does not change the analysis. Some 'winterizer' bags differ from the summer product only on the label
Common mistakes
- — Fertilising without a soil test, then adding phosphorus or lime that the soil did not need
- — Applying quick-release nitrogen into summer heat on a cool-season lawn, which drives disease more than growth
- — Comparing bags on price rather than on cost per pound of actual nitrogen
- — Using weed-and-feed and accepting the wrong timing for both jobs