Why New Sod Is Fed in Two Steps: The Science Behind UNDER SOD at Install and OVER SOD at 30 Days

As of September 2026. New sod is two plants in one month. On install day it is a mat of leaves with its roots cut off, living on stored sugar and whatever it can reach in the first inch of soil. Thirty days later it is a rooted lawn that can use nitrogen and iron and has no use for more phosphorus. One fertilizer cannot serve both, which is why the university establishment guides have always described two applications — a full dose incorporated into the soil before planting, and a lighter surface feeding once the grass is rooted — and why UNDER SOD™ and OVER SOD are built as Step 1 and Step 2 of one procedure rather than as two versions of the same bag. This is the science behind each step, with the sources.

Quick answer

• Step 1, UNDER SOD™, at install. One 25-pound bag per pallet (500 square feet), mixed into 4–6 inches of soil beneath the new sod before finish grade, once. 4-2-5, iron-free, with mycorrhizae, Bacillus and Trichoderma, humic and fulvic acid, and seaweed. Its job is rooting: phosphorus, potassium, and biology where the new roots go.
• Step 2, OVER SOD, at 30 days. One 25-pound bag per four pallets (2,000 square feet), spread on the lawn once a corner won’t lift, watered in. Planned analysis 8-0-6 with 2 percent non-staining iron: phosphorus-free, nitrogen mostly slow-release, potassium continued, iron for color now that there are roots to use it.
• Why two steps: the first month is about roots and soil contact; the second is about leaf and color. Phosphorus and biology belong in the soil at day one. Nitrogen and iron belong on the surface at day 30. Reversing either order costs roots.

The two steps at a glance

Every design decision, and the evidence behind it

What we don’t claim

UNDER SOD™ does not claim to make sod root faster than the universities’ incorporated rate would; it is that rate, with the biology and the soil chemistry carried in at the same depth. The mycorrhizal, Bacillus, and Trichoderma quantities are label numbers and will be printed when the label is; nothing here is a yield claim. OVER SOD’s analysis is a target until its guaranteed analysis exists. And neither bag replaces a soil test on a lawn that has a problem — the two steps are the right default for new sod on ordinary Northeast soil, which is most of it.

What happens to sod in the first 30 days

Sod is harvested with a half inch to three-quarters of an inch of soil, which means the roots that made it a lawn on the farm are almost entirely severed. What arrives on the pallet is a mature canopy on a shallow root plate, living on carbohydrate reserves in the crowns. The first job after install is not growth; it is re-rooting — “tacking” or “pegging” — the initiation of new roots from the crowns and the remaining root plate down into the prepared soil beneath. On cool-season grasses in good conditions that takes roughly 7 to 14 days to the point where a corner resists lifting, and 4 to 6 weeks to the point where the lawn is on its own.

Three things govern how fast that happens. Contact: roots initiate into firm, moist soil, which is why the seedbed is rolled and the sod is watered within the hour. Moisture: the root plate dries in hours in wind and sun, so the first two weeks are a watering schedule before they are anything else. And what the new roots find when they arrive: phosphorus is taken up by roots in the soil solution immediately around them and moves very little, so it has to be where the roots are going, not on top of the leaves.

There is a fourth factor, and it runs the other way. Nitrogen drives leaf growth, and a plant pushed to grow leaves before it has roots does so at the expense of the roots. High nitrogen at planting lowers the root-to-shoot ratio; the turfgrass literature has said so for fifty years. That is the reason the establishment guides put the heavy nitrogen after rooting, not before, and it is the reason Step 1 is a 4, not a 12 or a 24.

Step 1: why the fertilizer goes under the sod, not on it

The universities have never recommended laying sod on a bare grade and hoping. They recommend incorporating fertilizer and lime into the soil first, at a real rate, and they publish the depth. The complete sod installation guide puts that preparation in the context of the full install.

Rutgers’s sodding fact sheet, “Steps to an Instant Lawn,” calls for 30 to 40 pounds of 5-10-10 or a similar starter per 1,000 square feet, with lime and soil amendments, incorporated thoroughly with a rototiller to a depth of at least 6 inches. That is 1.5 to 2 pounds of nitrogen, 3 to 4 pounds of phosphate, and 3 to 4 pounds of potash, in the soil, before the sod. Michigan State’s sod guide puts 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. Its 1983 sod bulletin called for 10 to 15 pounds of 5-20-20 into the upper 3 to 4 inches. Missouri tills amendments and fertilizer into the top 4 to 6 inches, and Cornell’s lawn program says pH materials are easiest to mix into the upper 4 to 6 inches before planting. Clemson’s establishment guide draws the conclusion: fertilization after transplanting should not be needed, because fertilizer was incorporated into the soil before transplanting.

UNDER SOD™ is that incorporated dose. One bag per pallet, mixed into 4–6 inches of soil beneath new sod before finish grade, once at install, delivers 2 pounds of nitrogen, 1 pound of phosphate, and 2.5 pounds of potash per 1,000 square feet — inside the university preplant range on nitrogen and potash, and deliberately below it on phosphorus, for a reason covered below.

Incorporation is also why the rate is safe. Fertilizer burn is a concentration problem at the root tip. The same 50 pounds that would be dangerous raked into the top inch is unremarkable blended through 4 inches: 12 pounds in the top inch of 1,000 square feet is 12 pounds in about 7,000 pounds of soil, and 50 pounds through the top 4 inches is 50 pounds in about 28,000 pounds — the same concentration per pound of soil, roughly a fifth of one percent, and a third less at 6 inches. What changes is the depth of rooting profile carrying the nutrients, which is the point.

Why 4-2-5, and why no iron

Phosphorus at 2, in the soil. New roots need phosphorus where they are, and Connecticut’s and New York’s lawn-fertilizer laws both recognize it: phosphorus is prohibited on established lawns without a soil test and allowed when establishing a new lawn from seed or sod. UNDER SOD™ uses that exception once, under the roll, at 1 pound of phosphate per 1,000 square feet. That is a quarter to a third of the Rutgers preplant figure, and it is held there on purpose: most Northeast soils test sufficient to high in phosphorus already, and, as the next section explains, more phosphorus than the roots need works against the fungi placed with it. See the Connecticut lawn rules for the state rule in its local context.

Potassium at 5. Potassium is the stress nutrient — drought, heat, wear, cold. Turfgrass fertility references have long documented its role in water regulation and winter hardiness, and the older sod bulletins put 2 to 3 pounds of potash in the preplant layer. A potassium-forward analysis at install, 2.5 pounds per 1,000, is the university approach with a modern number.

Nitrogen at 4. Two pounds per 1,000, mostly slowly available, blended through the profile, is a rooting dose, not a color dose. It matches the upper end of Rutgers’s incorporated rate and stays below the point where leaf growth outruns roots.

No iron. Iron produces color without growth: the classic Kentucky bluegrass work at Illinois showed foliar iron greened the turf where nitrogen would have pushed leaf. Unrooted sod cannot use that, and a customer who sees a dark green mat on day five and stops watering has been misled by the bag. UNDER SOD™ leaves iron out so that the only thing the first month rewards is rooting. Iron is Step 2’s job.

The biology, and why it goes in the contact zone

Mycorrhizae. Arbuscular mycorrhizal fungi colonize grass roots and extend the root system’s reach for phosphorus and water; that is what they are for. In turf specifically, inoculating with Glomus species improved the establishment of landscape turf grown with no irrigation or fertilizer inputs in the Laval University work, which is as close to a stress test of a new lawn as the literature offers. They also respond to phosphorus in a way that matters for a starter fertilizer. A meta-analysis of field studies found that phosphorus additions reduced mycorrhizal colonization by roughly a third on average. Plants with easy phosphorus support fewer fungal partners. That is the second reason UNDER SOD™ holds phosphorus at 2 rather than 10 or 18: the fungi placed at the root plate need the roots to want them. The four species in UNDER SOD™ are named on the label and they are in the granule that is mixed into the soil, which is the only place spores reach the roots they are meant to colonize.

Bacillus and Trichoderma. The named Bacillus strains and the two Trichoderma strains are root-zone organisms: they colonize the rhizosphere, and the Trichoderma T-22 strain in particular has decades of published work on root colonization and plant response. They belong under the sod for the same reason the fungi do — they have to be where the roots are — which is why OVER SOD carries no live biology at all.

Humic and fulvic acid. Humic substances applied to the root zone increased rooting in the creeping bentgrass work at Clemson, and they buffer nutrient availability in the layer where the new roots are working. UNDER SOD™ carries 6 percent because the soil-building dose belongs at install; OVER SOD is planned to carry less because that work is already in the profile.

Seaweed. Ascophyllum nodosum extract has been associated with improved stress tolerance and root growth in turf, including in the Virginia Tech work on cytokinin-containing seaweed and humic extracts. In Step 1 that is transplant stress; in Step 2 it is mowing, heat, and the first traffic.

Step 2: what changed at 30 days, and why OVER SOD is built the way it is

By day 30 the tug test passes, the roots have moved into the soil, and the lawn has been mowed. Rutgers says a newly sodded lawn contains adequate nutrients for at least six weeks after placement and to fertilize when color and growth begin to fade. Michigan State says to fertilize the sod after 4 to 6 weeks of growth. The window is not arbitrary; it is the point where nitrogen goes to a plant that can use it.

Planned phosphorus-free analysis. At 30 days there is no reason to add phosphorus and two reasons not to. The roots are in the soil where UNDER SOD™’s phosphate already is, and more of it on the surface would suppress the mycorrhizae that just colonized them. OVER SOD’s planned phosphate is held at or below 0.67 percent, which Connecticut’s fertilizer law treats as phosphorus-free, so the same bag is intended to be legal at 30 days under the new-lawn exception and legal in any later season without a soil test. One bag, both jobs.

Planned nitrogen at 8, mostly slow. One bag per four pallets is 12.5 pounds per 1,000 square feet: about 1 pound of nitrogen, which is the standard first follow-up rate for cool-season turf, with most of it planned to be slowly available so the lawn thickens over weeks instead of flushing over days.

Planned iron at 2, now. This is the ingredient Step 1 withheld. Rooted sod uses iron for chlorophyll, and iron gives color without the leaf push of extra nitrogen. OVER SOD targets a non-staining form so a lawn that wraps a pool patio doesn’t leave rust on the coping.

Planned potassium at 6. The target stress package continues into the first summer or the first winter, whichever comes first.

A target medium granule, no biology. SGN 150 to 180 is planned to spread evenly and not track onto pavers; and surface-applied spores at day 30 do not reach the contact zone the way incorporated ones did at day 1, so OVER SOD does not pretend otherwise.

What goes wrong with the usual approaches

A high-phosphorus starter raked into the top inch at install. This is the universities’ second step performed without the first — Missouri’s “work starter into the top inch” comes after “till fertilizer into the top 4 to 6.” Done alone at full rate, it concentrates fertilizer at the root tip, puts 3 to 4 pounds of phosphate on a soil that usually doesn’t need it, and leaves nothing in the profile where the roots are headed.

A high-phosphorus starter on top at 30 days. Illegal on an established lawn in Connecticut and New York without a soil test, and, per the mycorrhizal literature, the fastest way to undo the colonization that Step 1 paid for.

A high-nitrogen synthetic at 30 days. Color in 48 hours, shoots over roots, and burn risk on a lawn that is a month old. The rooted plant can use a pound of mostly slow nitrogen; it cannot use two pounds of soluble. The Honest Comparison explains the under-sod options by the same evidence standard.

OVER SOD at UNDER SOD™’s rate. One bag per pallet is a soil rate. On the surface it is 2 pounds of nitrogen on 500 square feet of month-old sod. The bags say four pallets for a reason.

What the two steps put down

That is a rooting budget followed by a color budget, with phosphorus where the roots are and nothing on top that the law, the fungi, or the roots would object to.

Timing, by season and by law

Fall install: UNDER SOD™ once at install, OVER SOD at 30 days, then the normal fall feeding if the calendar allows. Spring install: UNDER SOD™ once at install, OVER SOD at 30 days, then the seasonal schedule for the grass; a second light feeding in early summer only on irrigated lawns heading into heat.

The one rule that overrides the 30 days is the blackout. Connecticut bars lawn fertilizer from December 1 through March 15; New York from December 1 through April 1, with Suffolk County starting November 1 and Nassau November 15. If the 30-day mark lands inside the window, OVER SOD waits for the first allowed date. UNDER SOD™ is not affected, because a new lawn’s install is inside the establishment exception and the phosphate is incorporated, not surface-applied.

Water buffers apply in both steps: no fertilizer within 20 feet of water in Connecticut and New York, 3 feet in New York with a drop spreader or a deflector.

The procedure in one line

One UNDER SOD™ bag per pallet at install, mixed into 4–6 inches of soil beneath the new sod before finish grade, once. Leave it alone for 30 days. One OVER SOD bag per four pallets at 30 days, watered in. Then the seasonal schedule for the grass and the region. Both UNDER SOD™ and OVER SOD are pre-launch and scheduled to ship through CT Sod in spring 2027. Until then, the 30-day feeding is a phosphorus-free slow-release lawn fertilizer at about a pound of nitrogen per 1,000 square feet.

FAQ

Why can’t one fertilizer do both jobs?

Because the plant changes. At install it has no roots and needs phosphorus, potassium, and biology in the soil; at 30 days it has roots and needs nitrogen and iron on the leaf, and no more phosphorus. A bag built for one is wrong for the other.

Why does UNDER SOD™ have less phosphorus than a starter?

A starter is built for seed on bare soil. Sod arrives with a root plate, most Northeast soils already test sufficient in phosphorus, and phosphorus additions reduce mycorrhizal colonization by about a third in field studies. One pound of phosphate per 1,000 square feet, in the soil, is enough for the roots and little enough for the fungi.

Why no iron in UNDER SOD™ and iron in OVER SOD?

Iron gives color without growth. Unrooted sod can’t use it and a dark green mat on day five tempts people to stop watering. Rooted sod at 30 days can use it, and it greens the lawn without pushing leaf over root.

Is 25 pounds per 500 square feet too much for a 4-2-5?

Not when it’s mixed through 4–6 inches beneath new sod before finish grade. Fifty pounds through the top 4 inches of 1,000 square feet is the same concentration per pound of soil as 12 pounds raked into the top inch, and Rutgers’s own sodding sheet incorporates 30 to 40 pounds of 5-10-10 to 6 inches.

Why is OVER SOD phosphorus-free?

Because Step 1 already put the phosphorus under the roll, because more of it on the surface suppresses the mycorrhizae, and because OVER SOD’s planned phosphorus-free analysis is intended to be legal in every later season without a soil test.

When exactly is 30 days?

When a corner of the sod won’t lift. In spring and fall that’s usually 3 to 5 weeks; in heat, 4 to 6. If the date lands in a state blackout, wait for the first allowed date.

What if I only use UNDER SOD™?

It does the rooting job on its own. At 30 days, feed once with a phosphorus-free slow-release lawn fertilizer at about a pound of nitrogen per 1,000 square feet, and skip anything with a high middle number.

Sources

Extension and university publications:

• Rutgers NJAES, FS104, “Sodding: Steps to an Instant Lawn”: 30 to 40 lb of 5-10-10 per 1,000 sq ft incorporated to at least 6 inches; adequate nutrients for at least six weeks after placement. Rutgers FS104
• Rutgers NJAES, FS584, “Seeding Your Lawn”: lime and fertilizer incorporated 4 to 6 inches deep; preplant fertilizer tilled 3 to 4 inches. Rutgers FS584
• Michigan State University Extension, E2911, “Sod Installation” (2004): lime and fertilizer into the top 4 inches; 10 lb of 10-10-10 per 1,000 sq ft; fertilize after 4 to 6 weeks of growth. MSU E2911
• Michigan State University Cooperative Extension, E1490, “Establishing a Lawn from Sod” (1983): 10 to 15 lb of 5-20-20 or 6-24-24 per 1,000 sq ft into the upper 3 to 4 inches. MSU E1490
• University of Missouri Extension, G6700, “Cool-Season Grasses: Lawn Establishment and Renovation”: amendments and fertilizer tilled into the top 4 to 6 inches, then starter worked into the top inch. Missouri G6700
• Clemson Cooperative Extension, HGIC, “Lawn Establishment”: fertilization after transplanting should not be needed because fertilizer was incorporated before. Clemson lawn establishment
• Mississippi State University Extension, “Sod Installation and Maintenance”: amendments incorporated in the top 6 to 10 inches where roots grow. Mississippi State sod installation and maintenance
• Cornell University Turfgrass Program, “Feeding”: pH materials mixed into the upper 4 to 6 inches before planting; New York fertilizer blackout dates. Cornell feeding guide
• Connecticut lawn-fertilizer law: see the CT DEEP page linked from the Connecticut lawn-rules page.
• New York Nutrient Runoff Law: NYS DEC lawn fertilizer page.

• Treseder, K.K. 2004. “A meta-analysis of mycorrhizal responses to nitrogen, phosphorus, and atmospheric CO2 in field studies.” New Phytologist 164(2): 347–355. DOI — phosphorus additions reduced mycorrhizal colonization by roughly a third on average across field studies.
• 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. Inoculation improved establishment of low-input turf.
• Yust, A.K., D.J. Wehner, and T.W. Fermanian. 1984. “Foliar application of N and Fe for Kentucky bluegrass.” Agronomy Journal 76: 934–938. Iron improved color without the growth response of nitrogen.
• Cooper, R.J., C. Liu, and D.S. Fisher. 1998. “Influence of humic substances on rooting and nutrient content of creeping bentgrass.” Crop Science 38: 1639–1644.
• Zhang, X., and E.H. Ervin. 2004. “Cytokinin-containing seaweed and humic acid extracts associated with creeping bentgrass leaf cytokinins and drought resistance.” Crop Science 44: 1737–1745.
• Harman, G.E. 2000. “Myths and dogmas of biocontrol: changes in perceptions derived from research on Trichoderma harzianum T-22.” Plant Disease 84: 377–393.
• Carrow, R.N., D.V. Waddington, and P.E. Rieke. 2001. Turfgrass Soil Fertility and Chemical Problems: Assessment and Management. Ann Arbor Press. Potassium and stress tolerance; nitrogen and root-to-shoot balance.
• Beard, J.B. 1973. Turfgrass: Science and Culture. Prentice-Hall. Sod establishment physiology; nitrogen’s effect on root growth.