Walk into any garden center and you will find a shelf of bags labeled "starter fertilizer for seed and sod." Almost none of them are made for the job you are actually doing. "Seed and sod" lumps two different problems into one product, and the difference matters most in the few inches of soil directly beneath newly laid turf. This is an honest comparison of what people actually put under new cool-season sod, Kentucky bluegrass, tall fescue, ryegrass, and fine fescue lawns from New England to the upper Midwest and the Pacific Northwest, scored bag by bag on their own labels against what the university turf programs say the fertilizer under sod has to do. UNDER SOD™ is the product we recommend, so weigh the source accordingly; we have tried to be straight about when something else is the better choice, because on a job that runs into the thousands, the wrong fertilizer is an expensive mistake.
Quick answer, as of September 2026. Test the soil first; an $18 UConn test decides the only thing that changes the answer. On a soil test that comes back low in phosphorus, a legal high-phosphorus starter at the report's rate, mixed in, is the right first bag, and UNDER SOD™ is a supplement. Thirty days later the feeding is phosphorus-free on either path. The 4-2-5 with no iron and four species of mycorrhizae, one 25-pound bag per pallet mixed into the top 4 to 6 inches, is UNDER SOD™; the 8-0-6 with 2 percent non-staining iron, one 25-pound bag per four pallets at 30 days, is OVER SOD™.
The sod fertilizer series, in order: read the soil test → the bag under the sod (this post) → the 30-day feeding on top → why it is two steps.
Seed and sod are not the same problem
Seed starts from nothing, bare soil and no roots, and it genuinely benefits from phosphorus to build a root system from scratch, which is exactly why classic starter fertilizers are phosphorus-heavy. Sod is a different problem. It arrives with a mature root system grown on the farm and cut off at harvest; its job in the first weeks is to bridge those roots down into your soil, not to build them from zero. On established cool-season lawns, three things make the old high-phosphorus reflex the wrong default.
Most established cool-season lawns already test medium to high in phosphorus. Native soils across the North are often low in phosphorus, but decades of fertilizing have pushed established lawn soils up, and phosphorus binds tightly and accumulates rather than washing away. Cornell puts the rule in one sentence: only if phosphorus is low should a fertilizer with phosphorus be used, and UConn's own report drops to a nitrogen-only recommendation when phosphorus and potassium are at or above optimum.
Excess soluble phosphorus suppresses mycorrhizae. The fungi that extend a young root system's reach are paid for by the plant's need for phosphorus; a meta-analysis of field studies found phosphorus additions reduced mycorrhizal colonization by roughly a third on average. When soil phosphorus is already high, the lawn tends to root shallower and stay more input-dependent.
Most cool-season states restrict phosphorus on lawns. Minnesota went first in 2005, and at least a dozen states now have the same shape of rule, among them Wisconsin, Michigan, Illinois, Maryland, Virginia, Washington, Vermont, Maine, New York, New Jersey, Massachusetts, and Connecticut, whose 2013 law restricts phosphorus on established lawns unless a soil test from the last two years shows a need; UConn's soil lab explains it. Every one of those laws permits phosphorus when seeding or sodding a new lawn, which is what makes a starter legal under sod on a low test. It does not make it useful on a high one.
Before anything else, get a soil test. Your state's land-grant lab runs one for about $20 (UConn's is $18) and gives you your real phosphorus number; how to read a report, and why the labs' scales do not match each other, is in What Your Soil Test Means for New Sod. If the test comes back low, a phosphorus starter is justified and legal for a new install. For most established cool-season lawns it comes back adequate to high, and then the right move under sod is low phosphorus plus biology, not more phosphorus. The scorecard below assumes that typical soil, with a separate column for the low test.
What the fertilizer under sod has to do: the rubric, before any product is named
The fertilizer under new sod is the preplant application the university establishment guides have always described: a full dose mixed into the soil before the turf goes down, matched to the soil test, so the severed roots land on it. Seven requirements fall out of those guides and the research. The first five come from the universities and the literature; the last two come from the field. Each is a column in the scorecard.
On a medium-to-high test the labs recommend little or no phosphate for turf (Cornell; UConn), and New York's fertilizer FAQ cites Cornell research finding no turf benefit above 4 ppm of Morgan phosphorus. Under new sod the establishment exception allows a light dose at the root, which is where the severed roots need it; the university preplant blends put roughly a pound of phosphate per 1,000 square feet into the soil (Michigan State's no-test default is 10 pounds of 10-10-10). A bag passes if its label rate delivers about a pound of P2O5 per 1,000 or less and its label does not call for a second phosphate application on the established lawn.
2. Potash at least equal to the nitrogen
Every university preplant blend for sod carries potash at or above the nitrogen: Michigan State's 10-10-10, Rutgers' 5-10-10 in FS104, the 5-20-20 of Michigan State's 1983 sod bulletin, and UMass recommends a one-to-one nitrogen-to-potassium ratio for late-season feeds. Potassium is what a rootless mat spends on water regulation before it is a nutrition problem. A bag passes if K2O is at least equal to N on the label.
3. Nitrogen moderate and mostly slow-release: no more than 2 pounds in the soil, at least 30 percent slow (60 on sand)
Michigan State incorporates about a pound of nitrogen per 1,000 before sod; Rutgers allows 1.5 to 2 pounds in its no-test default. Above that, or in soluble form, nitrogen pushes leaf the roots cannot support and burns. Cornell Cooperative Extension sets the slow-release floor at 30 percent on loam and 60 percent on sand. A bag passes if its label rate puts no more than 2 pounds of nitrogen per 1,000 in the soil and its slow-release share meets Cornell's line.
4. Made to be mixed into the soil, with a depth on the label
Michigan State incorporates lime and fertilizer into the top 4 inches as the final grade is prepared, Rutgers puts lime and fertilizer 4 to 6 inches deep before seeding or sodding, and Missouri tills amendments into the top 4 to 6 inches. Phosphorus does not move in soil; a bag spread on the surface under sod puts it in the wrong inch. A bag passes if its label says to incorporate it before sod and gives a depth or a preplant rate.
5. Living biology in the contact zone
This one comes from the research rather than the extension guides. Arbuscular mycorrhizal inoculation at establishment improved turf establishment without irrigation or fertilizer inputs (Pelletier and Dionne 2004), and inoculum only works where it touches new roots, which is the soil under the sod on day one. A bag passes if its label guarantees mycorrhizal propagules or named root bacteria.
6. No iron at installation
A field requirement. Iron greens leaf. On a rootless mat, a dark green day-five lawn tells the homeowner to stop watering, and the roots have not caught up. The two bags of the two-step system split iron on purpose: none under the sod, 2 percent on top at 30 days. A bag passes if the label lists no iron.
7. A sod rate printed on the bag
Also a field requirement. Sod is bought in 500-square-foot pallets and the bag goes in once, by whoever is standing on the graded soil; a bag that says one bag per pallet gets mixed in at the right rate, and a bag labeled in square feet for a seedbed gets whatever the tailgate math produces. A bag passes if the label gives a sod-specific rate; a per-pallet rate is the version that gets followed.
The scorecard
Five products people actually put under cool-season sod, scored on their own labels against the seven requirements for the typical medium-to-high phosphorus test. The last column scores the same bag on a low test.
| Product | Analysis and label rate under sod | 1. Phosphate fits the typical test | 2. Potash at least equal to N | 3. Nitrogen moderate, mostly slow | 4. Labeled to mix into the soil | 5. Biology | 6. No iron at install | 7. Sod rate on bag | Score (typical test) | On a low-P test |
|---|---|---|---|---|---|---|---|---|---|---|
| UNDER SOD™ | 4-2-5; one 25 lb bag per pallet = 50 lb per 1,000 mixed into the top 4 to 6 in; four endomycorrhizal species, Bacillus, Trichoderma, 6% humic, 2% kelp, SGN 90 | Pass (1.0 lb P2O5, once) | Pass (1.25 × N) | Pass (2.0 lb N, target 75% water-insoluble) | Pass (4 to 6 in on the bag) | Pass | Pass (iron-free) | Pass (one bag per pallet) | 7 of 7 | Supplement only: follow the report's phosphate with a starter |
| Milorganite 6-4-0 | 6-4-0; label for new lawns: mix into the top 2 in before sodding, 64 lb per 2,500 sq ft = 25.6 lb per 1,000; 4% water-insoluble N; 2.5% iron | Pass (1.0 lb P2O5 at the sod rate) | Fail (no potash) | Pass (1.5 lb N; 67% slow) | Pass (top 2 in on the label) | Fail (heat-dried biosolids, no live inoculant) | Fail (2.5% iron) | Pass (a sodding rate per 2,500 sq ft) | 4 pass, 3 fail | Close (1.0 lb P2O5) |
| Scotts Turf Builder Starter Food 24-25-4 | 24-25-4; 3 lb per 1,000 (15 lb covers 5,000); apply immediately before or after planting, again at 2 to 4 weeks | Fail (0.75 lb P2O5, then a second phosphate application on the established lawn) | Fail (0.17 × N) | See bag (0.72 lb N; slow-release share not published) | Fail (spread over the area, not incorporated) | Fail | Pass (no iron listed) | Close (sod named, seed rate) | 1 pass, 1 close, 4 fail, 1 see bag | Pass (a legal starter at the report's rate) |
| Jonathan Green Veri-Green Seeding and Sodding 12-18-8 | 12-18-8; 3 lb per 1,000; urea, polymer-coated urea, MOP, DAP; 25 to 30% slow-release; humates | Pass (0.54 lb P2O5) | Fail (0.67 × N) | Close (0.36 lb N; 25 to 30% slow, under Cornell's 30 on some listings) | Fail (apply anytime seed or sod is used; surface) | Fail | See bag (retailer listings differ on iron) | Close (sod named, seed rate) | 1 pass, 2 close, 3 fail, 1 see bag | Pass (a legal starter at the report's rate) |
| Generic 10-10-10 | 10-10-10; 10 lb per 1,000 is Michigan State's no-test preplant default; all quick-release | Pass (1.0 lb P2O5) | Pass (1.0 × N) | Fail (1.0 lb N, all soluble) | Close (the universities incorporate it; the bag does not say so) | Fail | Pass | Fail | 3 pass, 1 close, 3 fail | Close (1.0 lb P2O5) |
Not scored: compost and topsoil. Compost is an amendment, not a targeted establishment fertilizer; its nutrient content is variable and it does not replace the bag. Work it into the soil for structure and biology, then feed with a fertilizer that fits the test. It is a partner to the fertilizer step, not a substitute.
What separates UNDER SOD™ from the other four bags is design, not track record: no iron under the sod, potash carried above the nitrogen, phosphate held to a pound on a soil that has enough, and one bag per pallet printed on the front. On a low phosphorus test the scoring flips, the starters in the middle of the table become the right call at the report's rate, and UNDER SOD™ is the supplement, not the plan. A hot starter will also win the day-14 color photo; a bag with no iron and mostly slow nitrogen greens up slower on purpose.
How much of each bag for your lawn
Pick the bag, the size, and the soil test result, and the calculator prints pounds to buy, what the bag delivers per 1,000 square feet, whether it fits the test, and where it goes.
How much of each bag under the sod
Pick the bag and the size; add the soil test if you have it. Every rate is the label's.
UNDER SOD™: 100 lb for 2,000 sq ft, one 25 lb bag per pallet: 4 bags of 25 lb for 4 pallets.
Per 1,000 sq ft that delivers 2 lb of nitrogen (mostly slow-release (water-insoluble target 75% of N)), 1 lb of phosphate, and 2.5 lb of potash; iron none; with living mycorrhizal inoculum.
Soil test phosphorus optimum: This is the soil it was built for. One bag per pallet, mixed in, no starter.
Placement: mixed into the top 4 to 6 inches of prepared topsoil before the finish grade, one 25 lb bag per pallet. Lay the sod the same day, roll, and water.
Thirty days after installation, once the sod passes the tug test, the feeding on top is phosphorus-free on every path.
Rates from the labels in the Sources list. Reading the test: What Your Soil Test Means for New Sod. The feeding at 30 days: the 30-day feeding scorecard.
How much of each per pallet
Sod is sold by the 500-square-foot pallet, so here is each label rate in the unit people have in front of them. Amounts are for the typical test; on a low test the starter rate comes from the report.
| Product | Per pallet (500 sq ft) | Per acre (87 pallets) | What it delivers per 1,000 sq ft | Where it is sold |
|---|---|---|---|---|
| UNDER SOD™ | One 25 lb bag, mixed 4 to 6 in deep | 87 bags | 2 lb N, 1 lb P2O5, 2.5 lb K2O, plus the biology | |
| Milorganite 6-4-0 | 12.8 lb, mixed into the top 2 in | about 35 bags of 32 lb | 1.5 lb N, 1 lb P2O5, no potash | Home centers and hardware stores |
| Scotts Turf Builder Starter 24-25-4 | 1.5 lb, surface | about 9 bags of 15 lb | 0.72 lb N, 0.75 lb P2O5, 0.12 lb K2O | Home centers and hardware stores |
| Jonathan Green 12-18-8 | 1.5 lb, surface | about 9 bags of 15 lb | 0.36 lb N, 0.54 lb P2O5, 0.24 lb K2O | Hardware stores and garden centers |
| Generic 10-10-10 | 5 lb, incorporated | about 9 bags of 50 lb | 1 lb each of N, P2O5, and K2O | Farm and hardware stores |
Why the rate is a bag per pallet, and why it goes 4 inches down
University turf programs have recommended a full dose of fertilizer worked into the soil before sod for forty years, and the depth they publish is 4 inches. Michigan State University Extension's sod guide says to incorporate lime and fertilizer into the top 4 inches as the final grade is prepared, with a no-soil-test default of 10 pounds of 10-10-10 per 1,000 square feet, a pound each of nitrogen, phosphate, and potash. Its earlier sod bulletin called for 10 to 15 pounds of 5-20-20 per 1,000 into the upper 3 to 4 inches: 2 to 3 pounds of potash and 2 to 3 pounds of phosphate. Rutgers puts lime and fertilizer 4 to 6 inches deep and preplant fertilizer 3 to 4. University of Missouri Extension tills amendments and fertilizer into the top 4 to 6 inches and then, as a separate second step, works a light starter into the top inch.
UNDER SOD™ is that first step. One 25-pound bag per 500 square feet puts 1 pound of phosphate and 2.5 pounds of potash per 1,000 into 4 to 6 inches of soil beneath new sod, inside the preplant range Michigan State has published since 1983, with the biology and the humic and seaweed fractions carried in at the same depth.
The fertilizer calculators that tell you to rake 12 pounds of a 4-2-5 into the top inch are describing the universities' second step without the first, and the salt math is the same either way. Twelve pounds raked into the top inch of 1,000 square feet is 12 pounds in about 7,000 pounds of soil. Fifty pounds mixed through the top 4 inches is 50 pounds in about 28,000 pounds of soil, the same concentration at the root, about a fifth of one percent by weight, and through 6 inches it is a third less. Same exposure per pound of soil; four times the rooting profile carrying it.
The two bags, one procedure
UNDER SOD™ does the rooting job. What it deliberately does not do is green the lawn: no iron, and a potassium-forward 4-2-5 rather than a nitrogen-forward feed, because unrooted sod cannot use canopy nitrogen and does not need color. Thirty days after installation the situation flips: the roots have tacked, the mycorrhizae are colonizing, and the plant can use nitrogen and iron. That is the job of OVER SOD™, the phosphorus-free surface feeding built to pair with it, one 25-pound bag per four pallets, 8-0-6 with 2 percent non-staining iron.
What we do not claim
- On a below-optimum phosphorus test, UNDER SOD™'s pound of phosphate is a supplement, not a correction; follow the report and use a starter at its rate.
- Slow-release shares for the Scotts and Jonathan Green starters are taken from listings and vary by version; the bag in your hand governs.
Bottom line: which should you buy?
- Test your soil first. It is $18 and it answers the only question that changes the answer. How to read the report.
- If your soil tests low in phosphorus, a starter fertilizer mixed into the top 4 to 6 inches at the report's rate is the right, legal call for a new install; Scotts, Jonathan Green, or a starter all do the job, and UNDER SOD™ can go in with it for the biology.
- If your soil tests adequate to high, which is most established cool-season lawns, skip the high-phosphorus starter. Use a low-phosphorus, potassium-forward bag with biology, mixed into the soil under the sod.
- Either way, work compost into the soil for structure if you have it, alongside the fertilizer, not instead of it, and feed phosphorus-free at 30 days.
The honest summary: most fertilizers sold for new lawns are made for seed and sod. UNDER SOD™ is made for the one job those do not address, the contact zone beneath newly installed sod. Match the product to your soil test, and on a sod install worth thousands, that small upfront decision is the cheapest insurance you will buy.
Related reading
- What Your Soil Test Means for New Sod: reading a UConn, UMass, Rutgers, or Cornell report before you fertilize
- The Best Fertilizer for On Top of New Sod: Four Bags Scored for the 30-Day Feeding: the second step, scored the same way
- Why New Sod Is Fed in Two Steps: the rooting biology, phosphorus law, and university numbers behind the sequence
- The Truth About Phosphorus and New Sod: the full science on why the high-phosphorus reflex is usually wrong
- When to Fertilize New Sod in New England: the establishment-and-seasonal feeding timeline
- Fertilizer Mistakes That Kill New Sod: the eight feeding mistakes that do the damage
- Phosphorus Lawn Fertilizer Laws, State by State: the regulations and the new-sod exemptions
- UNDER SOD™, fertilizer built for beneath new sod: specification and application rate
Sources
- Michigan State University Extension E2911, Sod Installation
- Michigan State University Cooperative Extension E1490, 1983 sod bulletin
- Rutgers NJAES FS104, Sodding: Steps to an Instant Lawn
- Rutgers NJAES FS584, Seeding Your Lawn
- University of Missouri Extension G6700
- Cornell Turfgrass, Feeding
- Cornell Cooperative Extension, Monroe County, Fertilizing Your Lawn
- UMass Extension, Understanding the Turf Fertilizer Label
- UConn Soil Nutrient Analysis Laboratory, Standard Nutrient Analysis and Your Lawn and the Phosphorus Law
- New York DEC, Lawn Fertilizer FAQ
- Minnesota Department of Agriculture, Phosphorus Lawn Fertilizer Law (the first state law, 2005; new-turf and soil-test exemptions)
- Treseder, K.K. 2004. A meta-analysis of mycorrhizal responses to nitrogen, phosphorus, and atmospheric CO2 in field studies. New Phytologist 164: 347–355. DOI
- Pelletier, S., and J. Dionne. 2004. Inoculation rate of arbuscular-mycorrhizal fungi Glomus intraradices and Glomus etunicatum affects establishment of landscape turf with no irrigation or fertilizer inputs. Crop Science 44: 335–338.
- Milorganite product analysis and 32 lb bag label
- Scotts Turf Builder Starter Food for New Grass
- Jonathan Green Veri-Green Seeding and Sodding label and product page
Ready To Order?
Fresh-Cut Sod Delivered
CT Sod delivers Kentucky Bluegrass, Tall Fescue & RTF sod across CT, MA, NY, NJ, RI, NH, VT & ME.
From The Field
Our Recent Sod Installation Work
Frequently Asked Questions
What is the best fertilizer to put under new sod?+
Is Scotts Turf Builder Starter or Jonathan Green Seeding & Sodding good for new sod?+
Is Milorganite good under new sod?+
Do you need a high-phosphorus starter fertilizer for sod?+
Can I use a 10-10-10 under sod?+
What is OVER SOD™?+
Why no phosphorus in OVER SOD™?+
How deep does the fertilizer go before sod?+
Isn't a bag per pallet a lot for a 4-2-5?+
Keep Reading
Sod Fertilizer Job-Site Cards: One Page per State, Ready to Print
Sod on New-Construction Soil: What the Builder's Fill Is Missing, and What Goes Under It
Do You Need Starter Fertilizer for Sod? Only If Your Soil Test Says So
