Every fertilizer question about new sod in the Northeast comes back to one line on one piece of paper: the phosphorus line of a soil test. It decides whether the bag under the sod should carry phosphate or not, it decides what is legal to put down in Connecticut, Massachusetts, New York, and New Jersey, and it decides whether UNDER SOD™ is the right first bag or the wrong one. This post is about that piece of paper: how to get it from the four Northeast university labs, why their numbers do not match each other, and what each result means for a sod install.
Quick answer, as of September 2026. Test the soil the sod will root in, before the sod is ordered, at one of the four Northeast land-grant labs: UConn, UMass, Rutgers, or Cornell through Agro-One. Read the phosphorus line first. If the report says phosphorus is below optimum, put a high-phosphorus starter into the soil at installation at the report's rate; that is legal in every Northeast state under the new-lawn exception. If it says optimum or above, which is what most established Northeast lawns return, skip the high-phosphorus starter and use UNDER SOD™, one bag per pallet mixed into the top 4 to 6 inches. Follow the report's lime line at the same time. Thirty days later the feeding is phosphorus-free on either path. The four labs use two different extractants and three different units, so a number from one report cannot be read on another lab's scale; use the category the lab prints, not the number.
Why the test decides the bag
A soil test decides the fertilizer under new sod because phosphorus does not move in soil and cannot be measured by looking at the lawn. Nitrogen changes week to week and is applied by the calendar; phosphorus and potassium sit where they are, sometimes for decades, and Cornell's turf program puts it plainly: soil testing measures the availability of phosphorus and potassium, not nitrogen, and only if phosphorus is low should a fertilizer with phosphorus be used. Decades of lawn fertilizer have pushed most established Northeast lawns to medium or high phosphorus, while fill and scraped subsoil on new construction often test low. Those two soils need opposite bags under the sod, and the test is the only way to tell them apart.
The law follows the same line. Connecticut allows phosphorus on an established lawn only when a soil test from the last two years calls for it, and allows it when seeding or sodding a new lawn; UConn's soil lab explains the rule. New York allows phosphorus on established turf only when a soil test shows a deficiency or when a new lawn is being established, and the state's own FAQ notes Cornell research found no turf benefit above 4 ppm of Morgan-extractable phosphorus. Massachusetts and New Jersey require a soil test within three years to put phosphorus on an established lawn; the details are on the Massachusetts and New Jersey rules pages. The new-lawn exception is what makes a starter legal under sod on a low test. It does not make it useful on a high one.
How to take the sample for a sod job
Sample the soil the sod will actually root in. If the job is bringing in 4 to 6 inches of screened topsoil over the old grade, test that topsoil, not the lawn it is replacing; the roots will spend their first season in the imported layer. If the sod is going on the existing grade after tilling, sample the existing soil. On new construction, sample after the rough grade is set, because the top of a scraped lot is often subsoil that tests nothing like the topsoil that was hauled away.
Cornell's method is the one every lab accepts: use a soil corer or a trowel to gather 10 to 20 subsamples at a consistent depth from a uniform area, mix them in a clean bucket, air-dry the mix, and send the amount the lab's form asks for (UMass wants one cup, Rutgers two). Sample to the depth the lab's instructions give (Rutgers says 6 to 7 inches for a home lawn) and keep every core the same depth; for a sod job that is also close to the depth the fertilizer will be mixed into. Keep separate samples for areas that are obviously different, a sunny front and a shaded back, or the old lawn and a new fill pad. Allow at least two weeks, longer in spring. UConn's standard test is $18, and the other three labs are in the same range.
The recommendation on the report depends on what you tell the lab you are growing, and a new lawn is not the same crop code as an established one. UMass will not print lime or nutrient recommendations without a crop code; use the home-lawn code so the numbers come back per 1,000 square feet, and follow its sampling instructions (one cup, air-dried, $20). Rutgers takes a kit from a county extension office or a mailed sample with its home and landscape questionnaire, which asks what you are planting so the recommendation fits a new lawn; its sampling instructions call for 10 to 15 cores 6 to 7 inches deep. In New York, Cornell Cooperative Extension sends samples to Agro-One on the Home Garden and Lawn form with the standard package. UConn sells prepaid kits through extension centers and takes mailed samples; ask for the lawn recommendation. On every form, name the sample so you can match it to the area, and write the square footage.
The four labs, side by side
The four Northeast land-grant labs do not report on the same scale. UConn, UMass, and Cornell use the Morgan or modified Morgan extractant, developed at UConn in the 1930s for New England soils; Rutgers uses Mehlich-3, a stronger extractant that pulls more phosphorus out of the same soil. Units differ too: UConn and Cornell report pounds per acre, UMass reports parts per million, and Rutgers reports pounds per acre (its ppm figure times two). Cornell's Nutrient Management Spear Program says outright that results from one method cannot be read against another method's calibration, and the conversion tool it offers for Mehlich-3 to Morgan equivalents needs the soil's pH, calcium, and aluminum, not just the phosphorus number. So the table below carries the categories each lab prints, and the number ranges only where the lab publishes them. When you use the reader further down, enter the category from your report.
| Lab | Who uses it | Extractant and units | What the report prints | Published phosphorus and potassium ranges |
|---|---|---|---|---|
| UConn Soil Nutrient Analysis Laboratory (Storrs) | Connecticut | Modified Morgan; pounds per acre | Below Optimum, Optimum, Above Optimum for P, K, Ca, Mg; a lime rate in pounds per 1,000 sq ft; a nitrogen-only recommendation when P and K are at or above optimum | Lab's published table: phosphorus below optimum 0 to 13, optimum 14 to 20, above optimum 21 and up; potassium below optimum 0 to 249, optimum 250 to 349, above optimum 350 and up (lb/acre) |
| UMass Soil and Plant Nutrient Testing Laboratory (Amherst) | Massachusetts; the test the state law names for established lawns | Modified Morgan; parts per million | Your value next to an optimum range for each nutrient; a lime recommendation from buffer pH | Lawn reports show an optimum range of 4 to 14 ppm phosphorus and 100 to 160 ppm potassium; UMass turf guidance treats above 10 ppm P and above 100 ppm K as adequate |
| Rutgers Soil Testing Laboratory (New Brunswick) | New Jersey | Mehlich-3; pounds per acre (ppm × 2) | A bar for each nutrient marked Below Optimum (very low, low, medium), Optimum (high), or Above Optimum (very high), per fact sheet FS719 | Category-based; the lab publishes crop-specific cutoffs (for example, above 50 lb P/acre is adequate for a tree crop) rather than one lawn number |
| Cornell guidelines through Agro-One (Dairy One, Ithaca) | New York | Morgan; pounds per acre | A bar from Very Low to Very High with Cornell's recommendation lines; order the standard package on the Home Garden and Lawn form | Category-based; Cornell research cited by NY DEC found no turf benefit above 4 ppm Morgan phosphorus |
Two things follow from that table. First, the same lawn can read 12 at UConn and 40 at Rutgers and be the same soil; do not compare numbers across labs. Second, the category is what the lab's fertilizer recommendation is built on, and the category is what the state law reads. Everything below is keyed to the category.
Reading the phosphorus line
The phosphorus category on a Northeast soil test decides which bag goes under the sod: below optimum means a high-phosphorus starter at the report's rate, optimum or above means a low-phosphorus rooting bag. Three outcomes.
Below optimum (Very Low, Low, or Medium on a Rutgers or Cornell bar)
Phosphorus is genuinely short, which is common on stripped subsoil, new-construction fill, sand, and old farm fields that were never limed. The report prints a phosphate number in pounds of P2O5 per 1,000 square feet (or per acre; divide by 43.56). Put that phosphate into the soil at installation, mixed 4 to 6 inches deep with the lime, using a legal high-phosphorus starter such as an 18-24-12 or a 12-18-8 at the rate that delivers the report's number; every Northeast state allows it when establishing a new lawn. UNDER SOD™'s pound of phosphate per 1,000 is not built for a deficient site, and the honest answer on this test is the starter first, at the report's rate. Once the sod is rooted, the surface feeding at 30 days is still phosphorus-free; the phosphate you put in the soil is where the roots are.
Optimum (High on a Rutgers or Cornell bar)
This is the test most established Northeast lawns return, and it is the soil UNDER SOD™ was built for. The lab's own recommendation on this result is nitrogen, with little or no phosphate, because more phosphorus does not improve turf and, on an established lawn, is not legal without the test. Under sod, the establishment exception allows a light dose at the root, which is what UNDER SOD™'s 4-2-5 carries: one bag per pallet mixed into the top 4 to 6 inches puts 1 pound of phosphate per 1,000 square feet where the severed roots land, with the potassium and the biology in the same layer. The under-sod comparison is the full case for that bag against the alternatives.
Above optimum (Very High)
Phosphorus does nothing for the sod on this soil, and it can suppress the mycorrhizal colonization a rooting bag is trying to establish. The law still allows phosphate at installation, but the lab is telling you not to add any. UNDER SOD™ remains a reasonable rooting bag here because its phosphate is small and sits inside the establishment window, but if the report flags phosphorus as excessive, the cleaner choice is a phosphorus-free slow-release bag mixed to the same 4-to-6-inch depth, with lime and potassium per the report. Either way, nothing with a middle number goes on top of this lawn again without a new test.
Reading the potassium line
Potassium is the second line, and it changes the rate, not the bag. A below-optimum potassium test is common on sandy shoreline soils, because potassium leaches from low-CEC sand (UMass's interpretation guide says as much), and the report prints a potash number to build the level back. UNDER SOD™ delivers 2.5 pounds of K2O per 1,000 square feet at installation and OVER SOD™ another 0.75 at 30 days, which covers a typical build recommendation for a lawn; if the report asks for more than that, make up the difference with sulfate of potash (0-0-50) mixed in at installation. On an optimum test, the two bags maintain it. On an above-optimum test, no extra potash, and the two bags' potassium is still within a normal season's application.
pH and lime: the line people skip
New England soils run naturally acidic, 4.5 to 5.5 by UMass's account, and cool-season turf wants 6.0 to 7.0. Below about 6.0 phosphorus locks up, aluminum comes into solution, and the bacteria in the soil slow down, which is a bad combination for a bag that relies on biology. The report gives a lime rate from the buffer pH; that rate is the one to use, not a rule of thumb. At installation, lime goes in with the fertilizer: Michigan State's sod guide has incorporated lime and fertilizer into the top 4 inches as the final grade is prepared since 2004, and Rutgers puts lime 4 to 6 inches deep before seeding or sodding (FS584). If lime is applied to the surface later instead, UConn caps a single surface application at 50 to 75 pounds per 1,000 square feet and repeats at intervals; a big correction takes a season either way. Sulfur lowers pH when a soil tests above 7.0; UMass gives 5 to 10 pounds per 1,000 for about half a unit, never more than 15 in one application.
Soil test reader for new sod
Enter the lab that ran your test and the categories it printed. The reader turns them into the install bag, the potassium and lime notes, the 30-day feeding, and the legal note for your state. It reads the category on your report; it does not convert numbers between labs.
Soil test reader for new sod
Enter what the report prints. Numbers are read only for UConn (lb/acre) and UMass (ppm); every other lab uses the category.
Phosphorus: Optimum. This is the soil UNDER SOD™ was built for. Under the sod: UNDER SOD™, one 25 lb bag per pallet, mixed into the top 4 to 6 inches before the finish grade: 4 bags of 25 lb for 2,000 sq ft. No high-phosphorus starter; the lab's own recommendation on this result is nitrogen with little or no phosphate.
Potassium: Optimum. The two bags maintain it: 2.5 lb of K2O per 1,000 sq ft at installation and 0.75 lb at 30 days. No extra potash.
pH 5.6: below the 6.0 to 7.0 range for cool-season turf. Apply lime at the rate the report prints (it is set from the buffer pH, not from the pH alone) and mix it into the top 4 to 6 inches with the fertilizer before the finish grade. If lime has to go on after the sod is down, keep a single surface application to 50 to 75 lb per 1,000 sq ft and repeat at intervals.
At 30 days, after the tug test: a phosphorus-free feeding at 0.75 to 1.0 lb of nitrogen per 1,000 sq ft on every path (OVER SOD™ one bag per four pallets when it ships; LESCO 24-0-11 at 4.2 lb per 1,000 until then). The 30-day feeding scorecard compares the bags.
Connecticut: phosphorus may go on an established lawn only when a soil test from the last two years recommends it; seeding or sodding a new lawn is exempt, so a starter is legal under sod on a low test. Keep this report; it is your legal basis for two years.
Rules: Connecticut lawn rules page. Bags at 30 days: the 30-day feeding scorecard.
If you would rather have a person read it: send a photo of the report through the contact page with the town and the square footage, or call (203) 806-4086 with it in front of you, and we will tell you which bag goes under the sod and what the report's lime line means for the install.
Four soils, four reports
The 30-year lawn being replaced
Optimum or above-optimum phosphorus, optimum potassium, pH in the mid 5s. This is the typical Fairfield County or Westchester result. Lime per the report, UNDER SOD™ one bag per pallet, phosphorus-free at 30 days. No starter.
The new-construction pad
Below-optimum phosphorus and potassium, low organic matter, pH anywhere. This is subsoil. Bring in topsoil if the budget allows and test the topsoil; if the sod is going on the pad, put the report's phosphate and potash in with a starter and lime, 4 to 6 inches deep, and treat UNDER SOD™'s pound as a supplement, not the plan. The biology matters most on this soil, which is the one honest argument for adding UNDER SOD™ on top of a starter here: the mycorrhizae have nothing to work with in fill until something inoculates it.
The shoreline sand
Phosphorus optimum, potassium below optimum, pH often above 6 near salt water. Potassium is the story: the report's potash number, sulfate of potash at install if UNDER SOD™'s 2.5 pounds does not reach it, and a slow-release share of at least 60 percent on every nitrogen feeding, which is Cornell's rule for sand and the reason the 30-day feeding scorecard scores that column.
The lot next to the pond
Any phosphorus result, but a 20-foot buffer in Connecticut and New York and a blackout calendar. The test still decides the bag; the state pages decide where and when it can go down.
What we do not claim
- The ranges in the table are the labs' published categories; the labs revise them, and the report in your hand governs. We do not convert numbers between extractants and neither should a calculator.
- A soil test does not measure nitrogen usefully in a humid climate; nitrogen is set by the calendar and the grass, not the report.
- UNDER SOD™'s phosphate is 1 pound per 1,000 square feet at installation, on a planned label. That is a low-test supplement, not a low-test fix; on a below-optimum report, follow the report.
- No independent trial has compared rooting bags across soil-test categories on new sod. The advice above is the labs' guidance applied to the two-step sequence, not a trial of this product.
The procedure, in one place
- Sample the soil the sod will root in: 10 to 20 cores, 4 inches deep, mixed; the imported topsoil if you are bringing some in.
- Send it to your state's land-grant lab (UConn, UMass, Rutgers, or Cornell through Agro-One) two to three weeks before the sod is ordered.
- Read phosphorus first. Below optimum: a high-phosphorus starter at the report's rate, mixed 4 to 6 inches deep. Optimum or above: UNDER SOD™, one bag per pallet, same depth.
- Read potassium. Make up any shortfall with sulfate of potash at installation.
- Lime at the report's rate, mixed in with the fertilizer, before the finish grade.
- Lay the sod the same day the soil is finished, roll, water.
- At 30 days, after the tug test, a phosphorus-free feeding on every path; the bags are compared in the 30-day feeding scorecard.
- Keep the report. In Connecticut it is your legal basis for two years, in Massachusetts and New Jersey for three.
Why the first bag goes under the sod and the second stays phosphorus-free is in Why New Sod Is Fed in Two Steps and Why OVER SOD™ Exists. The sod-prep sequence the test fits into is the sod installation guide.
Sources
- UConn Soil Nutrient Analysis Laboratory, and its published interpretation table for modified Morgan results
- UConn, Standard Nutrient Analysis fact sheet (nitrogen-only recommendation when P and K are above optimum; surface lime limits)
- UConn, Your Lawn and the Phosphorus Law
- UMass Soil and Plant Nutrient Testing Laboratory, Interpreting Your Soil Test Results
- UMass Extension, Understanding the Turf Fertilizer Label (adequate P and K thresholds)
- UMass sample lawn soil test report (optimum ranges printed on the report)
- UMass routine soil analysis form, home grounds and sampling instructions
- Rutgers NJAES FS719, Soil Fertility Test Interpretation
- Rutgers Soil Testing Laboratory, How to Have Your Soil Tested and its home and landscape sampling instructions
- Rutgers NJAES FS1187 (Mehlich-3 categories and the ppm to lb/acre conversion)
- Rutgers NJAES FS584, Seeding Your Lawn (lime and fertilizer incorporation depth)
- Cornell Turfgrass, Feeding (sampling method; P and K by soil test)
- Cornell, Soil Testing: Essential Management Tool (Agro-One with Cornell guidelines)
- Cornell Nutrient Management Spear Program, Fact Sheet 15 (methods are not interchangeable)
- Cornell Cooperative Extension Broome County, soil testing through Agro-One
- New York DEC, Lawn Fertilizer FAQ
- Michigan State University Extension E2911, Sod Installation
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