Under Sod 4-2-5 is blended into the top 4 to 6 inches of soil before the sod goes down. The label method is incorporation. If you cannot mix it in, use the quarter-rate topical application.
The rate is one 25-pound bag per pallet of sod (500 square feet), which is 50 pounds per 1,000 square feet, blended into the top 4 to 6 inches of soil.
Quick answer: what is under-sod fertilizer?
Under-sod fertilizer is blended into the top 4 to 6 inches of soil before the sod is laid, so nutrients and biology sit in the exact zone where new roots have to grow. Under Sod 4-2-5 is the trademarked product built for that job — an iron-free biological 4-2-5 granular pre-plant fertilizer with named endomycorrhizae, a *Bacillus* + *Trichoderma* biology package, seaweed, and humic acid, spread at one 25-pound bag per pallet of sod (500 square feet), which is 50 pounds per 1,000 square feet, blended into the top 4 to 6 inches of soil right before installation.
Why the rooting zone is the only thing that matters
When sod is harvested it loses almost all of its roots. A fresh roll arrives as grass on about half an inch of soil, and it survives on stored energy until it can grow new roots down into the ground beneath it. That thin boundary between the back of the sod and your graded soil — the soil-to-sod rooting zone — is where establishment is won or lost.
Broadcasting fertilizer on top of new sod fights both timing and placement. Granules sitting on the leaf blades have to be watered in, dissolve, and migrate down through the sod layer before roots ever reach them. Putting the feed under the sod flips that: roots meet nutrients and soil biology on day one, exactly where they are trying to anchor.
The old recommendation: "just use a starter fertilizer"
For decades the standard advice was to reach for a high-phosphorus starter — products labeled something like 18-24-12 or 10-20-10 — designed to push fast establishment with a big phosphorus spike. Those products work in the sense that phosphorus supports early root growth, but they were formulated for seeding a lawn from scratch, not for the specific conditions under a sod roll.
| Conventional high-P starter | Under Sod 4-2-5 approach | |
|---|---|---|
| Designed for | Seeding bare soil | The soil-to-sod rooting zone |
| Phosphorus | Very high (a spike) | Moderate, steady (2%) |
| Soil biology | Usually none | Endomycorrhizae + Bacillus + Trichoderma + seaweed + humic |
| Placement | Broadcast on top, watered in | Blended into the top 4 to 6 inches of soil, sod laid on top |
| Fit near water | Often too hot | Lower-P, iron-free, easier to justify |
Designed for
Conventional high-P starter
Seeding bare soil
Under Sod 4-2-5 approach
The soil-to-sod rooting zone
Phosphorus
Conventional high-P starter
Very high (a spike)
Under Sod 4-2-5 approach
Moderate, steady (2%)
Soil biology
Conventional high-P starter
Usually none
Under Sod 4-2-5 approach
Endomycorrhizae + Bacillus + Trichoderma + seaweed + humic
Placement
Conventional high-P starter
Broadcast on top, watered in
Under Sod 4-2-5 approach
Blended into the top 4 to 6 inches of soil, sod laid on top
Fit near water
Conventional high-P starter
Often too hot
Under Sod 4-2-5 approach
Lower-P, iron-free, easier to justify
The purpose-built answer: a biological under-sod pre-plant fertilizer
Under Sod 4-2-5 is formulated around the rooting zone rather than the leaf. The N-P-K is a K-forward, moderate-phosphorus 4-2-5, so there is enough phosphorus to support root initiation without the excess that can suppress beneficial fungi or run off near water — and it is iron-free, because the job is to root the sod, not to green the bag. The biological package does the heavy lifting: 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 with added fulvic acid to improve nutrient holding at the soil interface.
Because it is granular at SGN 90 and applied directly to graded soil, it stays exactly where you put it — no relying on a topical granule to wash down through the sod. Read the full breakdown on the product page, or compare it head-to-head in starter fertilizer vs. Under Sod 4-2-5.
Where Under Sod 4-2-5 fits
If you are laying sod and want the feed in the rooting zone from day one, Under Sod 4-2-5 is built for exactly that. See the full specs or join the notification list for product updates.
Always pair fertilizer choices with a soil test. Many states — including New York, New Jersey, Connecticut, and Florida — restrict phosphorus lawn fertilizer, though most rules exempt establishing a new lawn or a soil-test-shown deficiency, which is the sod-installation case. Rules are often stricter near lakes, rivers, and shorelines, so check your local and municipal requirements before applying.
Application rate
The rate is one 25-pound bag per pallet of sod (500 square feet), which is 50 pounds per 1,000 square feet, blended into the top 4 to 6 inches of soil. At that rate it delivers 1 pound of phosphate, 2 pounds of nitrogen and 2.5 pounds of potash per 1,000 square feet, in line with the preplant rates Michigan State publishes, at the 4-inch-plus depth Rutgers and Michigan State publish, for establishing a new lawn when a soil test calls for it. It is spread through roughly 17 tons of soil at a 5-inch midpoint (about 14 tons at 4 inches, 21 at 6) where new roots grow. Incorporation reduces surface exposure; it does not eliminate runoff risk.
How Under Sod is applied
- Spread one 25-pound bag per pallet of sod, 500 square feet (50 pounds per 1,000 square feet), evenly on the prepared, graded soil for blending into the top 4 to 6 inches in the next step.
- Rototill or Harley-rake it into the top 4 to 6 inches.
- Final grade and roll.
- Lay the sod and water in.
What actually goes down per 1,000 square feet
Percentage on the bag is not the same as dose on the lawn. These are the nutrient doses and placements at the rates shown below. Competitor rows are comparison examples, not verified current label rates.
| Product | Comparison rate per 1,000 sq ft | Nitrogen (lb) | Phosphate P2O5 (lb) | Potash K2O (lb) | Placement |
|---|---|---|---|---|---|
| Under Sod 4-2-5 | 50 lb (one bag per pallet) | 2.0 | 1.0 | 2.5 | Blended 4 to 6 inches deep |
| Over Sod 8-0-6 | 12.5 lb (one bag per four pallets) | 1.0 | 0 | 0.75 | Surface, at day 30 |
| Scotts Turf Builder Starter 24-25-4comparison example | 3 lb | 0.72 | 0.75 | 0.12 | Surface |
| Jonathan Green Veri-Green Starter 12-18-8comparison example | 3 lb | 0.36 | 0.54 | 0.24 | Surface |
Under Sod 4-2-5 and Over Sod 8-0-6 rows use this site's own rates. Rows marked "comparison example" use example rates supplied for this comparison; they have not been verified against each manufacturer's current label, which can differ by product version and use. Check the bag in hand. Nutrient pounds are rate times analysis.
Where it ends up in the soil
Soil test first. When not to use Under Sod covers low-phosphorus test results, high-phosphorus results, and local rules.
Frequently Asked Questions
Do you really put fertilizer under sod?+
Yes. Applying a starter to the finished soil before laying sod places nutrients and soil biology directly in the rooting zone, where new roots grow down. That is the entire idea behind Under Sod 4-2-5.
What is the best fertilizer to put under new sod?+
A K-forward, moderate-phosphorus biological pre-plant fertilizer built for the rooting zone — named endomycorrhizae plus a *Bacillus* + *Trichoderma* package and humic acid — rather than a hot high-phosphorus lawn starter. See best fertilizer under sod for the full comparison.
Is Under Sod 4-2-5 the same as a regular starter fertilizer?+
No. Regular starters are formulated to seed bare soil with a phosphorus spike. Under Sod 4-2-5 is an iron-free 4-2-5 biological pre-plant fertilizer formulated specifically for the soil-to-sod interface. Compare them in starter fertilizer vs. Under Sod 4-2-5.
How much Under Sod 4-2-5 do I need?+
The rate is one 25-pound bag per pallet of sod (500 square feet), which is 50 pounds per 1,000 square feet, blended into the top 4 to 6 inches of soil. Count your pallets to count your bags.
Can I use it near the water?+
Its moderate 2% phosphorus and iron-free formula make it easier to justify in phosphorus-restricted and waterfront areas than a hot starter, but you should always confirm local rules and use a soil test. See best fertilizer under sod for waterfront.
Keep reading
Step two
Day 30: OVER SOD™ 8-0-6 is step two, a phosphorus-free surface feed with mostly slow-release nitrogen, at one 25-pound bag per four pallets of sod (2,000 square feet), which is 12.5 pounds per 1,000 square feet: about 1 pound of nitrogen, 0.75 pound of potash, and no phosphate. Water it in. If day 30 falls inside your state's fertilizer blackout, wait for the first allowed date. OVER SOD™ ships spring 2027. About Over Sod 8-0-6
Homeowners and installers are already asking what goes under new sod. Under Sod 4-2-5 is the brand built specifically for that job, blended into the soil. The label method is incorporation. If you cannot mix it in, use the quarter-rate topical application.
Built for beneath the sod.
A 4-2-5, iron-free biological pre-plant fertilizer — named mycorrhizae, beneficial bacteria, Trichoderma, seaweed, and humic acid — at one bag per pallet of sod (500 square feet), which is 50 pounds per 1,000 square feet, blended into the top 4 to 6 inches of soil.