Quick answer: the best fertilizer under sod in Pennsylvania
In Pennsylvania, the smartest thing to put under new sod is a low-phosphorus biological starter worked into the rooting zone — not a hot high-phosphorus lawn starter that the state's turf-fertilizer law (Act 83 of 2022) restricts and that new sod can't use fast enough anyway. Under Sod™ is built for exactly this: an iron-free 4-2-5 granular starter with named endomycorrhizae, a *Bacillus* + *Trichoderma* biology package, seaweed, and humic acid, spread at one 25 lb bag per 500 sq ft (one pallet of sod) on the graded soil before the sod goes down.
Why this matters in Pennsylvania
Freshly harvested sod arrives almost rootless on a thin pad of soil. It has days, not weeks, to push new roots down into the ground beneath it, and whatever is sitting in that soil-to-sod rooting zone is what those first roots find. Pennsylvania's rooting zone is unusually varied — acidic, stony sandstone soils on the ridges, deeper near-neutral soils in the limestone valleys, and different ground again on the Piedmont and the Allegheny Plateau — but on all of it, feed placed at the interface does far more for a new install than a granule broadcast on top.
There is a second reason to keep phosphorus modest here, and it is a big one: most of Pennsylvania drains through the Susquehanna into the Chesapeake Bay, and the state is the single largest source of nutrients to the Bay — with Lake Erie and the Delaware adding more watersheds. Pennsylvania's 2022 turf-fertilizer law is part of its Chesapeake commitments. Feeding the rooting zone directly, with a moderate 2% phosphorus, keeps nutrients where the roots are and lowers what can run toward the nearest stream.
Pennsylvania soils under new sod
Pennsylvania has some of the most varied soils in the Northeast. The official state soil, the Hazleton series, is an acidic soil formed from sandstone that covers roughly 1.5 million acres of the state's ridges — well-drained, stony, and low in natural fertility. Drop into the limestone valleys (the Great Valley and the limestone belts of the southeast), though, and the soils weather deeper, richer, and near-neutral in pH. So the ground under a Pennsylvania sod job can be acidic ridgetop till one town over from a fertile limestone loam.
That range changes how a feed behaves: on stony, acidic sandstone soils, phosphorus binds to aluminum and iron and becomes less available to roots, while on the deeper limestone valley soils the natural fertility means little added phosphorus is needed in the first place. On both, the same principle holds — keep the nutrients and biology at the soil-to-sod interface, held there by humic acid rather than washing through or perching on top — and living mycorrhizae that scavenge bound phosphorus do more for real uptake than a bigger P number. Lime the acidic sites to your soil test.
What Pennsylvania soil tests actually say about phosphorus
The standard reference in the state is the Penn State Agricultural Analytical Services Laboratory, which measures phosphorus with the Mehlich-3 extractant. For home lawns, Penn State uses a clear threshold: below about 45 ppm the lab recommends phosphorus, at or above 45 ppm it recommends none, and above roughly 200 ppm the level is considered an environmental concern. Many established Pennsylvania lawns test above the 45 ppm cutoff after years of fertilizing, which is why the honest move is to soil-test the graded surface first rather than assume a new install needs a phosphorus spike.
The old recommendation: "grab a high-phosphorus starter"
For years the default sod-install advice was a high-phosphorus starter — products labeled something like 18-24-12 or 10-20-10 — on the theory that a big phosphorus spike drives roots. Those blends were designed to seed a bare lawn from scratch, not to feed the interface beneath a sod roll. In Pennsylvania the fit is looser still: graded soils often already test above Penn State's 45 ppm cutoff, and — even though establishing turf is one of the exceptions the law allows — feeding phosphorus the soil doesn't need is exactly the loading the state's Chesapeake-driven rules are written to cut.
| Conventional high-P starter | Under Sod™ approach | |
|---|---|---|
| Designed for | Seeding bare soil | The soil-to-sod rooting zone |
| Phosphorus | Very high (a spike) | Moderate, steady (2%) |
| Vs. Penn State's 45 ppm cutoff | Overshoots it | Matches a real, tested need |
| In the Chesapeake watershed | Prone to run off | Held at the interface by humic acid |
| Soil biology | Usually none | Endomycorrhizae + Bacillus + Trichoderma + seaweed + humic |
| Fit with PA turf-fertilizer law | Often restricted | Lower-P, iron-free, easier to justify |
The better recommendation: a purpose-built biological under-sod starter
A starter built for the rooting zone fits Pennsylvania far better than a generic high-P blend. Under Sod™ carries a K-forward, moderate-phosphorus 4-2-5 N-P-K — enough phosphorus to support root initiation without an excess that leaches or runs off, with the raised potassium (5%) driving the cold-, drought-, and transplant-stress tolerance turf leans on — plus the biology that does the real work: named endomycorrhizae (*Rhizophagus irregularis, Funneliformis mosseae, Glomus aggregatum,* and *Glomus etunicatum*) to colonize and extend the new root system, a *Bacillus* consortium (*B. amyloliquefaciens, B. megaterium,* and *B. subtilis*) plus *Trichoderma* (*T. harzianum / T. virens*) to activate the root zone, 2% seaweed extract (*Ascophyllum nodosum*) for natural rooting compounds, and 6% humic acid (leonardite) with added fulvic acid to improve nutrient holding at the soil interface. It is iron-free by design — the goal is to root the sod, not to green the bag.
It is the right fit for the cool-season turf grown and laid across Pennsylvania — Kentucky bluegrass, tall and fine fescues, and perennial ryegrass blends, including the tall-fescue-heavy mixes common in the state's warmer southern counties. Because it is granular at SGN 90 and applied directly to graded soil, it stays where you put it instead of relying on a topical granule to wash down through the sod. Read the full breakdown on the product page, or see the broader best fertilizer to put under sod comparison.
Where Under Sod™ fits
If you are laying sod anywhere from the Philadelphia suburbs to the Susquehanna Valley and out to Pittsburgh and the Erie shore, and want the feed in the rooting zone from day one, Under Sod™ is built for that moment. It launches Fall 2026 across the Northeast through the CT Sod network. See the full specs or join the notification list to know when it ships to Pennsylvania.
Always pair fertilizer choices with a soil test. Pennsylvania's turf-fertilizer law — Act 83 of 2022 — requires that turf fertilizer contain no phosphorus except when it is labeled for establishing turf for the first time or for reestablishing or repairing turf (the sod-installation case), or for certain enhanced-efficiency or natural-organic products applied within a rate limit. The law also sets nitrogen rates, buffers near water, and frozen-ground limits. Under Sod's moderate 2% phosphorus and iron-free formula fit the establishment exemption, but always confirm current state and municipal requirements before applying.
Application rate
How to apply Under Sod™ on a Pennsylvania install
- Soil-test the graded surface first — for home lawns Penn State recommends no phosphorus once the soil reads 45 ppm or higher, so the test tells you whether any added phosphorus is warranted.
- Finish grading and final soil prep so you have a smooth, firm surface — clear the stone common in Pennsylvania's ridge-and-valley fill.
- Spread one 25 lb bag per 500 sq ft — that is one bag for every pallet of sod you are about to lay.
- Leave the granules on the soil surface; do not till them deep.
- Lay the sod directly on top, then water thoroughly to settle the sod and activate the biology.
One bag per pallet keeps the math simple on the job site: count your pallets, count your bags.
Frequently Asked Questions
What is the best fertilizer to put under new sod in Pennsylvania?+
A low-phosphorus biological starter placed in the rooting zone — not a hot high-phosphorus lawn starter that Pennsylvania's turf-fertilizer law (Act 83 of 2022) restricts. Under Sod™ is an iron-free 4-2-5 biological starter built for the soil-to-sod interface and suited to Pennsylvania's varied soils and its Chesapeake-driven rules.
Does Pennsylvania restrict phosphorus lawn fertilizer?+
Yes. Act 83 of 2022 requires turf fertilizer to contain no phosphorus except when labeled for establishing turf for the first time or reestablishing or repairing it — which covers a sod install — or for certain enhanced-efficiency or organic products within a rate limit. Nitrogen rates and near-water buffers also apply, so confirm current rules and use a soil test.
What phosphorus level do Pennsylvania soils usually have?+
By the Penn State Agricultural Analytical Services Laboratory test (Mehlich-3), home lawns reading 45 ppm or higher get no phosphorus recommendation, and above about 200 ppm the level is an environmental concern. Many established Pennsylvania lawns test above 45 ppm, so soil-test the graded surface before you install.
Why do Pennsylvania's soils vary so much?+
Pennsylvania's geology swings from acidic sandstone ridges — the source of its state soil, the Hazleton series — to deeper, near-neutral limestone valley soils, plus the Piedmont and Allegheny Plateau. That means pH and natural fertility can change from one job site to the next, so a soil test and a placement-first, moderate-phosphorus starter fit better than a fixed high-P spike.
Does Under Sod™ work with Pennsylvania grass types?+
Yes. It is formulated for the cool-season turfgrasses grown and laid across Pennsylvania — Kentucky bluegrass, tall and fine fescues, and perennial ryegrass blends, including the tall-fescue mixes common in the warmer southern counties.
How much Under Sod™ do I need?+
One 25 lb bag covers 500 sq ft, which is one standard pallet of sod. Count your pallets to count your bags.
When does Under Sod™ launch in Pennsylvania?+
Fall 2026, as part of the Northeast rollout through the CT Sod network. Join the notification list for launch and shipping alerts.
Keep reading
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 Fall 2026 across the Northeast.