The First and Only Fertilizer Made to Go Beneath New Sod.
A serious biological starter fertilizer for homeowners and professionals who care about doing things right.
Why Sod Needs a Different Fertilizer Than Established Lawns
Sod may look like a finished lawn when it's rolled out, but in reality, it's a living product that's just been through an intense trauma. When sod is harvested, its root system is severed — often cutting off more than half of its original roots. It's removed from its native soil, rolled up tightly, stacked on a pallet, and shipped off to a new location. From that point forward, it's in survival mode.
This process puts sod under immediate transplant stress, which can lead to:
- Dehydration, especially in warm weather
- Delayed root establishment in unfamiliar soil
- Yellowing or browning from nutrient deficiency
- Susceptibility to disease and heat stress
Sod has one urgent job when it hits the ground: establish new roots — fast.
Conventional starter fertilizers — the standard 18-24-12 and 12-25-12 high-phosphorus formulations sold at every retail chain — were developed before modern soil biology research was complete. They push fast top growth with concentrated phosphorus, but the high phosphorus levels actually suppress the mycorrhizal partnerships that new sod needs to develop deep, resilient roots. The grass establishes anyway because modern sod is tough — but it establishes despite the fertilization strategy, not because of it. And the lawn that grows in is structurally dependent on continued synthetic input for the rest of its life.
UNDER SOD™ takes a fundamentally different approach. Moderate, balanced nutrition paired with the biological inputs that build long-term soil function rather than suppress it.
How UNDER SOD™ Helps Sod Recover and Take Root
UNDER SOD™ is designed to be applied before the sod is installed, creating a rich, biologically active base layer that supports root regrowth from day one. Spread it on prepared soil, rake it in lightly, lay the sod, and water. The roots make immediate contact with the nutrients and biology exactly where they need it.
1.75% Mycorrhizal Fungi for Rapid Root Rebuilding
Our blend includes a potent dose of mycorrhizal inoculation. These fungi form a natural symbiotic relationship with your sod's newly forming roots, extending the effective root system through microscopic filaments. The turf absorbs more water and nutrients than it could on its own — especially critical during the first few days when the sod is reestablishing itself in new soil.
Mycorrhizal colonization can increase effective root surface area by up to 1,000 times — but only when soil conditions support it. Conventional high-phosphorus starters suppress this colonization. UNDER SOD™ is formulated specifically to enable it.
2% Seaweed Extract to Reduce Transplant Shock
We include seaweed extract from cold-water brown algae (Ascophyllum nodosum) because it contains natural plant hormones — cytokinins and auxins — that stimulate root initiation and reduce cellular stress during transplant. Seaweed helps sod bounce back faster, maintain hydration, and initiate the rooting process more quickly after installation.
6% Humic Acid to Build a Better Soil Environment
Humic acids drive cation exchange capacity (the soil's ability to hold nutrients in plant-available forms), chelate micronutrients to keep them accessible, and create the soil chemistry conditions that mycorrhizal partnerships require to establish. They also increase water retention — crucial during the first critical days after installation.
Most conventional starter fertilizers contain no humic acid at all. UNDER SOD™ contains it at the concentration soil chemistry research supports.
4-4-4 Slow-Release Nutrition That Feeds Without Burning
Our balanced 4-4-4 NPK base provides gentle nutrition that feeds the sod as it roots — without overwhelming or burning the tender roots that are just beginning to regrow. Moderate phosphorus supports immediate plant function without saturating the root zone and suppressing the mycorrhizal partnerships the rest of the formula is designed to establish.
The lower N-P-K numbers compared to conventional starters reflect a different biological strategy, not a less effective product. The biological components multiply the effective availability of the moderate nutrient load.
SGN 90 Granular Form
Fine-to-medium granule size (SGN 90) ensures even spreading and direct soil contact beneath the sod, with no large particles that could create hot spots or uneven coverage.
How to Apply UNDER SOD™
UNDER SOD™ ships in 25-pound bags calibrated to cover one 500 sq ft pallet of sod. One bag, one pallet. No measuring, no math, no spreader calibration calculations.
Prep the Soil
Rake level, remove debris, ensure good final grade.
Spread One Bag
Spread one bag of UNDER SOD™ per pallet of sod evenly across the prepared soil.
Rake It In
Lightly rake into the top 2-4 inches so the granules and biological inputs contact the soil surface where new roots will form.
Lay the Sod
Lay the sod immediately afterward. Roll for good soil-to-sod contact.
Water Thoroughly
1 inch of water the first day, then keep consistently moist for 2-3 weeks.
The Conventional Starter Fertilizer Problem
For decades, the standard recommendation for new sod has been a high-phosphorus starter fertilizer — formulations like 18-24-12, 12-25-12, or similar. These products were developed in an era when "feeding the plant" was the entire framework. Concentrated NPK delivered to the soil, plant takes up the nutrients, top growth appears, job done.
Modern soil biology research has shown the framework is incomplete. Specifically:
High soil phosphorus suppresses mycorrhizal colonization.
When plants can absorb phosphorus directly through their roots in high-P soil, they stop signaling for fungal partners. The symbiosis fails to form during the only window when it can be naturally established at the soil-sod interface.
Conventional starters contain no humic acid.
The soil chemistry foundation that holds applied nutrients in the root zone, chelates micronutrients, and supports biological activity is simply absent from the standard category.
Conventional starters contain no seaweed extract.
The hormonal support that helps sod through transplant shock — the moment the plant is most vulnerable — is missing.
The result: long-term dependence on synthetic inputs.
Sod establishes structurally dependent on continued synthetic input because the biological systems that would otherwise support it were suppressed during establishment. The lawn looks fine in the first month, then struggles through summer stress in ways biologically supported lawns don't.
UNDER SOD™ exists because the conventional category never solved this. Moderate NPK paired with the biological inputs that actually build long-term soil function is what new sod needs — and what the soil biology research has been pointing toward for years.
The Science Behind UNDER SOD™
Every component in UNDER SOD™ is included based on documented soil biology research. The four-pillar content library on CT Sod covers the underlying science in depth:
Best Fertilizer for New Sod
Why high-phosphorus starters fail and what works instead
Mycorrhizal Fungi and New Sod Rooting
The symbiotic partnership and how high-P suppresses it
Humic Acid and New Sod Establishment
The chemistry foundation conventional starters skip
Mycorrhizae, Humic Acid & Seaweed: The Biological Trinity
How the three components work together
Pre-Launch Notification List
UNDER SOD™ launches Fall 2026.
We're rolling out regionally through CT Sod's Northeast network first, then expanding through select regional partners.
Join the Notification List