How Under Sod is applied
Under Sod goes into the soil, not on it. One 25-pound bag covers 500 square feet — one bag per pallet of sod. Spread the bag over the prepared topsoil and mix it into the top 4 inches with a tiller, harrow, or power rake, up to 6 inches where the topsoil lift is deeper. Finish-grade, lay the sod the same day, roll, and water. Once. It is not raked into the top inch, it is not a surface starter, and it is not reapplied.
Blended through the rooting profile, that bag delivers 2 pounds of nitrogen, 1 pound of phosphate, and 2.5 pounds of potash per 1,000 square feet — the amounts sit where the roots go, not where the salt would.
After install: leave the lawn alone for a month, then feed once at one month, then follow the normal seasonal schedule for your grass and region. If the one-month mark falls inside your state’s fertilizer blackout, wait for the first allowed date.
An acre is 87 pallets and 87 bags.
Why the rate is what it is
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’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, which is 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. Missouri 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, done at the depth and in the range they published. One bag per 500 square feet puts 1 pound of phosphate and 2.5 pounds of potash per 1,000 into the top 4 inches, inside the university preplant range, with the biology and the humic and seaweed fractions carried in with it.
The online 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. The math is the same either way: 12 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, roughly 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 depth of rooting profile carrying it. That is why Under Sod is incorporated and why the rate is a bag per pallet.
| Under Sod, mixed in | Surface-applied starter | |
|---|---|---|
| Where it goes | Blended through the top 4 inches of prepared topsoil before sod, up to 6 where the topsoil lift is deeper | On the soil surface, or raked into the top inch |
| When | Once, before the sod is laid | Before sod, then often again at two to four weeks |
| How much | One 25-pound bag per 500 square feet of sod, one bag per pallet | Pounds per 1,000 square feet by label, typically 10 to 20 for a 4-4-4 |
| Phosphorus | 2 percent | 4 to 25 percent, built for seed on bare dirt |
| Biology | Mycorrhizae, Bacillus, Trichoderma, humic and fulvic acid, seaweed, placed at the root zone | None, or left on the surface where it dries |
| Built for | The soil under transplanted sod | Germinating seed |
Where it goes
Under Sod, mixed in
Blended through the top 4 inches of prepared topsoil before sod, up to 6 where the topsoil lift is deeper
Surface-applied starter
On the soil surface, or raked into the top inch
When
Under Sod, mixed in
Once, before the sod is laid
Surface-applied starter
Before sod, then often again at two to four weeks
How much
Under Sod, mixed in
One 25-pound bag per 500 square feet of sod, one bag per pallet
Surface-applied starter
Pounds per 1,000 square feet by label, typically 10 to 20 for a 4-4-4
Phosphorus
Under Sod, mixed in
2 percent
Surface-applied starter
4 to 25 percent, built for seed on bare dirt
Biology
Under Sod, mixed in
Mycorrhizae, Bacillus, Trichoderma, humic and fulvic acid, seaweed, placed at the root zone
Surface-applied starter
None, or left on the surface where it dries
Built for
Under Sod, mixed in
The soil under transplanted sod
Surface-applied starter
Germinating seed
Two products for two jobs
These are not two rates for the same product. They are two products for two jobs.
Application FAQ
How deep does Under Sod go?+
Into the top 4 inches of prepared topsoil, up to 6 where the topsoil lift is deeper. That is the depth Michigan State and Rutgers publish for fertilizer before sod. It is mixed in with a tiller, harrow, or power rake before the finish grade, not raked into the top inch.
Isn’t 25 pounds per 500 square feet a lot for a 4-2-5?+
It is the same concentration at the root as 12 pounds raked into the top inch, because it is mixed through four times the depth of soil. Fifty pounds per 1,000 square feet through the top 4 inches is 50 pounds in about 28,000 pounds of soil; 12 pounds in the top inch is 12 pounds in about 7,000. The potash and phosphate in that bag — 2.5 and 1 pound per 1,000 — sit inside the preplant range Michigan State has published for sod since 1983.
Can I put Under Sod down after the sod is laid?+
No. It is built to be mixed into the soil the sod roots into. After install, leave the lawn alone for a month, then feed once at one month, then follow the seasonal schedule for your grass and region.
University guidance behind the specification
The low-phosphorus position remains grounded in university guidance. The UConn Soil Nutrient Analysis Laboratory explains Connecticut's phosphorus rules for establishing turf, while Cornell's turfgrass resources provide regional guidance for New York soils and turf establishment.
The second half: Over Sod
Target analysis 8-0-6 with 2% iron. The final guaranteed analysis is set by the manufacturer’s label; these are the targets Over Sod is being built to.
| Nitrogen | Target: 8%, most of it slowly available from a slow-release nitrogen base, with a small soluble fraction for early color. |
| Phosphorus | Target: none added. Guaranteed phosphate is held at or below 0.67 percent, which is what Connecticut’s fertilizer law treats as phosphorus-free. Under Sod already placed the phosphorus the new lawn needs under the roll; a second dose on the surface would only shut down the mycorrhizae Under Sod put there. |
| Potash | Target: 6% from sulfate of potash, continuing the stress package Under Sod started for heat, traffic, and the first winter. |
| Iron | Target: 2% in a non-staining form. This is the ingredient Under Sod leaves out on purpose. Under Sod roots the sod. Over Sod greens it. |
| Humic and fulvic acids | Target: 3 to 4 percent, with target Ascophyllum seaweed at 1.5 to 2 percent, the same chemistry as Under Sod at a lighter dose, because the soil-building dose is already in the profile. |
| No live biology | Planned: no live biology. Surface-applied spores at one month don’t reach the contact zone the way Under Sod did; the biology story belongs under the roll. |
| Medium granule | Target: SGN 150 to 180 so it spreads clean and doesn’t track onto pavers or into the house. |
Nitrogen
Target: 8%, most of it slowly available from a slow-release nitrogen base, with a small soluble fraction for early color.
Phosphorus
Target: none added. Guaranteed phosphate is held at or below 0.67 percent, which is what Connecticut’s fertilizer law treats as phosphorus-free. Under Sod already placed the phosphorus the new lawn needs under the roll; a second dose on the surface would only shut down the mycorrhizae Under Sod put there.
Potash
Target: 6% from sulfate of potash, continuing the stress package Under Sod started for heat, traffic, and the first winter.
Iron
Target: 2% in a non-staining form. This is the ingredient Under Sod leaves out on purpose. Under Sod roots the sod. Over Sod greens it.
Humic and fulvic acids
Target: 3 to 4 percent, with target Ascophyllum seaweed at 1.5 to 2 percent, the same chemistry as Under Sod at a lighter dose, because the soil-building dose is already in the profile.
No live biology
Planned: no live biology. Surface-applied spores at one month don’t reach the contact zone the way Under Sod did; the biology story belongs under the roll.
Medium granule
Target: SGN 150 to 180 so it spreads clean and doesn’t track onto pavers or into the house.
Under Sod under the roll at install, mixed into the top 4 inches of prepared topsoil, one bag per pallet. Over Sod on the lawn at one month, one bag per four pallets. Then the seasonal schedule.
Homeowners and installers are already asking what goes under new sod. UNDER SOD™ is the trademarked brand built specifically for that job.
Built for beneath the sod.
A 4-2-5, iron-free biological starter — named mycorrhizae, beneficial bacteria, Trichoderma, seaweed, and humic acid — at one bag per pallet. Launching Spring 2027 across the Northeast.