Fertilizer Application Sheet
The one conversion that matters is pounds of NITROGEN to pounds of PRODUCT. Everything else on this sheet is downstream of it.
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The application
- Date
- Area (sq ft)
- Product
- N-P-K
- Nitrogen %
- lb N wanted per 1,000
- PRODUCT per 1,000 sq ft
- TOTAL PRODUCT
- Spreader setting
- Watered in?
The arithmetic
- The rule
- 1 lb ACTUAL NITROGEN per 1,000 sq ft per application
- Product needed
- lb N x 100 / the first bag number
- 16-4-8
- 100 / 16 = 6.25 lb product per lb N
- 20-0-0
- 100 / 20 = 5.0 lb product per lb N
- 10-10-10
- 100 / 10 = 10 lb product per lb N
- 32-0-4
- 100 / 32 = 3.13 lb product per lb N
- The three numbers are
- % by weight of N, P, K
- ⚠ Upper limit
- about 0.9-1 lb N per 1,000 per application
- ⚠ Excess nitrogen
- LEAVES — into ground and surface water
- ⚠ Slow-release
- read the BAG's own max rate; it wins
Applications through the season
| Date | Product | N % | lb N/1,000 | Total product | Weather / notes |
|---|---|---|---|---|---|
Before spreading anything
- SOIL TEST done — the only thing that knows your lawn
- First bag number read, and the product-per-lb-N worked out
- Rate confirmed as pounds of NITROGEN, not pounds of product
- Local restrictions checked — phosphorus is regulated in many places
- Slow-release proportion read off the bag
- Spreader calibrated, and set for THIS product
- Applied in two passes at right angles for evenness
- Nothing spread on hard surfaces — sweep it back onto the grass
- Not applied before heavy rain
- Watered in if the label says to
Pounds of nitrogen, not pounds of fertilizer
A 16-4-8 bag is 16% nitrogen, so a pound of N takes 6.25 lb of product. Mixing the two up under-feeds by a factor of six in one direction, and in the other burns the lawn and runs off into the water. This single ratio is the whole calculation.
The recommended rate is a ceiling
Research indicates healthy turf can use around 0.9 lb of actual nitrogen per 1,000 sq ft per application, and more than that contributes to water degradation. Excess nitrogen does not wait in the soil — it leaves. This is one of the few garden numbers where exceeding it is worse than falling short.
Sweep it off the pavement
Granules that land on a driveway or path do not feed anything and go straight into a storm drain with the next rain. Sweeping them back onto the grass takes a minute and is one of the highest-impact things on this sheet for water quality.