Quick answer: is 4-4-4 good under sod?
A balanced 4-4-4 will work under new sod — it gives even, gentle nitrogen, phosphorus, and potassium without the phosphorus spike of a traditional starter. But the rooting zone rewards a more specific ratio: lower phosphorus (so it doesn't suppress root-building fungi) and higher potassium (for stress tolerance). That's why Under Sod™ is a K-forward, iron-free 4-2-5 built for exactly this job, applied at one 25 lb bag per 500 sq ft (one pallet of sod) on finished soil before the sod goes down.
Why the NPK ratio matters in the rooting zone
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. Whatever nutrition sits in that soil-to-sod rooting zone is what those first roots find — so the ratio you choose is the most consequential fertilizer decision in the whole install.
The three numbers on a fertilizer bag are the percentages of nitrogen (N), phosphorus (P), and potassium (K) by weight. A 4-4-4 means equal, moderate amounts of each — a genuinely balanced ratio, and already a big improvement on a phosphorus spike: enough phosphorus to support early root growth, enough nitrogen and potassium for steady establishment, and nothing applied so hot it works against the soil biology. The open question is whether *equal* is the ideal split for a rooting zone — or whether you want less phosphorus and more potassium.
The old recommendation: high-phosphorus starters
For decades the standard advice was to reach for a high-phosphorus starter — products labeled something like 18-24-12 or 10-20-10 — built to drive fast establishment with a big phosphorus spike. They were formulated to seed a lawn from scratch on phosphorus-hungry, bare soil, and on that job they have a long track record. Under a sod roll the fit is looser: graded soils often already hold enough phosphorus, and a topical granule can end up sitting on the sod instead of in the rooting zone.
| 4-4-4 (balanced) | 10-10-10 (balanced, hotter) | 18-24-12 (high-P starter) | 4-2-5 (Under Sod™, K-forward) | |
|---|---|---|---|---|
| Designed for | Steady, even feeding | General-purpose feeding | Seeding bare soil fast | The soil-to-sod rooting zone specifically |
| Phosphorus | Moderate (4%) | Moderate (10%) | Very high (24%) — a spike | Low (2%) — mycorrhizae-safe |
| Potassium | Moderate (4%) | Moderate (10%) | Moderate (12%) | Raised (5%) — for stress tolerance |
| Nutrient release | Even, gentle | Even, stronger | Front-loaded P | Slow-release N, even |
| Fit under new sod | Solid, general fit | Workable, no biology | More P than graded soil needs | Purpose-built — low P, high K, live biology |
| Fit near water / P limits | Easier to justify | Check local rules | Often too high | Easiest — only 2% P, iron-free |
The better recommendation: a K-forward, low-phosphorus biological starter
Under new sod, the strongest setup isn't just a balanced ratio — it's a ratio tuned to the rooting zone. Under Sod™ is a K-forward, iron-free 4-2-5: nitrogen kept moderate and mostly slow-release, phosphorus dropped to 2% so it won't suppress the root-building fungi, and potassium raised to 5% for the drought, cold, and transplant-stress tolerance new sod needs most. Onto that ratio it layers the biology a plain bagged NPK can't: named endomycorrhizae (*Rhizophagus irregularis, Funneliformis mosseae, Glomus aggregatum, Glomus etunicatum*), a _Bacillus_ consortium (*B. amyloliquefaciens, B. megaterium, B. subtilis*) with *Trichoderma* (*T. harzianum, T. virens*) and a microbial carbon food source, plus 2% seaweed extract (*Ascophyllum nodosum*) and 6% humic acid with fulvic acid.
Because it is granular at SGN 90 and spread directly on graded soil, it stays exactly where you put it — in the rooting zone — rather than relying on a topical granule to wash down through the sod. The low 2% phosphorus avoids the excess that can suppress mycorrhizal colonization, while the higher potassium supports stress tolerance — the whole point of pairing a rooting-zone ratio with live biology. And because it is iron-free by design, it roots the sod rather than greening the bag: color is a cosmetic you can add later, but rooting is the decision you can't redo. See how it stacks up in starter fertilizer vs. Under Sod™ or read the full product specs.
Where Under Sod™ fits
If you want a rooting-zone starter — K-forward, low-phosphorus, iron-free 4-2-5 with the biology already built in — Under Sod™ is made 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.
Ratios are general guidance, not a substitute for a soil test. Many states — including New York, New Jersey, Connecticut, and Florida — restrict phosphorus lawn fertilizer, though most rules exempt new-lawn establishment or a soil-test-shown deficiency, which is the sod-installation case. Restrictions are often tighter near lakes, rivers, and shorelines, so confirm your local and municipal requirements before applying.
Application rate
How to apply Under Sod™ under new sod
- Finish grading and final soil prep so you have a smooth, firm surface ready for sod.
- 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
Is 4-4-4 a good fertilizer for under sod?+
A balanced 4-4-4 works — it gives even, moderate N-P-K for root initiation without a hot phosphorus spike. But under sod you can do better than equal numbers: less phosphorus (so it won't suppress root-building fungi) and more potassium (for stress tolerance). That's why Under Sod™ is a K-forward, iron-free 4-2-5 with named mycorrhizae, a Bacillus + Trichoderma package, seaweed, and humic acid for the rooting zone.
What does 4-4-4 mean on a fertilizer bag?+
It is the percentage by weight of nitrogen (N), phosphorus (P), and potassium (K). 4-4-4 means equal, moderate amounts of all three — a balanced ratio rather than one nutrient applied as a spike.
Is 4-4-4 better than 10-10-10 under new sod?+
Both are balanced, but 10-10-10 is more concentrated. Either will establish sod; the bigger win under sod is a ratio tuned to the rooting zone — lower phosphorus, higher potassium — plus soil biology, which is what Under Sod™'s 4-2-5 brings and a plain 10-10-10 does not.
Why not just use a high-phosphorus starter like 18-24-12?+
High-P starters were built to seed bare, phosphorus-hungry soil. Graded soil under sod often already has enough phosphorus, and excess P can suppress beneficial fungi and be restricted near water. Under Sod™ keeps phosphorus low at just 2% to avoid over-applying.
How much do I apply under sod?+
For Under Sod™, one 25 lb bag covers 500 sq ft — one standard pallet of sod. Count your pallets to count your bags, and apply to finished soil before laying the sod.
When does Under Sod™ launch?+
Fall 2026, starting in the Northeast U.S. 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.