Quick answer: the best fertilizer under sod on Long Island
On Long Island's sandy, fast-draining soils, the smartest thing to put under new sod is a moderate-phosphorus biological starter placed right in the rooting zone — not a hot high-phosphorus lawn starter that leaches toward the aquifer. 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 on Long Island
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. On Long Island that zone has a particular character: much of Nassau and Suffolk sits on sandy glacial outwash that drains fast and holds nutrients poorly, so a feed that washes through quickly does the new roots little good.
There is a second reason placement matters here. Long Island draws its drinking water from a sole-source aquifer directly below those sandy soils, which is exactly why New York and Suffolk County regulate lawn phosphorus and nitrogen so closely. Feeding the rooting zone directly — rather than broadcasting a soluble spike on top and watering it in — keeps nutrients where the roots are and lowers the amount that can leach down.
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, and on Long Island's leachy sand the spike is more likely to move past the roots than to stay put.
| 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%) |
| On sandy LI soil | Leaches quickly past roots | Held at the interface by humic acid |
| Soil biology | Usually none | Endomycorrhizae + Bacillus + Trichoderma + seaweed + humic |
| Fit with NY / Suffolk rules | Often too hot | 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 Long Island 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 — 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 that improves nutrient holding in exactly the sandy soils that struggle to keep nutrients around. 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 Long Island — Kentucky bluegrass, tall and fine fescues, and perennial ryegrass blends. 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 in Nassau or Suffolk 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 Long Island.
Always pair fertilizer choices with a soil test. New York restricts phosphorus lawn fertilizer, but the rules generally exempt establishing a new lawn or a soil-test-shown deficiency — which is the sod-installation case. Suffolk County layers on additional local requirements, including seasonal application windows, and rules are typically stricter near bays, ponds, and shoreline. Under Sod's moderate 2% phosphorus and iron-free formula are the relevant angle for these regulated, aquifer-sensitive areas, but always confirm your current town, county, and state requirements before applying.
Application rate
How to apply Under Sod™ on a Long Island install
- Finish grading and final soil prep so you have a smooth, firm surface — especially important on loose, sandy 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 on Long Island?+
A moderate-phosphorus biological starter placed in the rooting zone — not a hot high-phosphorus lawn starter that leaches through sandy soil. Under Sod™ is an iron-free 4-2-5 biological starter built for the soil-to-sod interface and suited to Long Island's leachy soils and phosphorus rules.
Why does Long Island's sandy soil change the fertilizer choice?+
Much of Nassau and Suffolk sits on fast-draining sand that holds nutrients poorly, so a soluble phosphorus spike can leach past the roots before they use it. A starter held at the interface by humic acid, with moderate phosphorus, keeps the feed where new roots are growing.
Is high-phosphorus fertilizer allowed for new sod in New York?+
New York restricts phosphorus lawn fertilizer, but the rules generally exempt establishing a new lawn or a documented soil-test deficiency — which covers a sod install. Suffolk County adds its own local requirements, so always confirm current town, county, and state rules and use a soil test.
Does Under Sod™ work with Long Island grass types?+
Yes. It is formulated for the cool-season turfgrasses grown and laid across Long Island — Kentucky bluegrass, tall and fine fescues, and perennial ryegrass blends.
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.
Is it a good choice near the water?+
Its moderate 2% phosphorus and iron-free formula make it easier to justify in phosphorus-restricted and shoreline areas than a hot starter, but you should always confirm local rules and use a soil test. See best fertilizer under sod for waterfront.
When does Under Sod™ launch on Long Island?+
Fall 2026, as part of the Northeast rollout through the CT Sod network. Join the notification list for launch and shipping alerts.
Keep reading
- Best fertilizer under sod in New York (Upstate & Hudson Valley)
- Best fertilizer under sod in New Jersey
- Best fertilizer under sod in Connecticut
- Best fertilizer under sod for waterfront properties
- Best fertilizer to put under sod
- Best sod fertilizer on Long Island — install day to first season
- See the full product specs
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.