Quick answer
Scotts Turf Builder Starter is a high-phosphorus synthetic starter built to feed a new lawn broadly; Under Sod™ is a low-phosphorus, potassium-forward biological starter built specifically for the root-contact zone beneath new sod. On most Northeast soils — which already test adequate-to-high in phosphorus — the low-P biological approach fits new sod better. Scotts' high-P starter is the better pick when a soil test shows a phosphorus deficiency.
Scotts Turf Builder Starter, fairly
It's a well-known, widely available synthetic starter formulated with a high phosphorus number to feed new grass — seed or sod — across the board. It's easy to find, consistent, and does what it's designed to do: deliver a broad synthetic feed to a new lawn. For a homeowner whose soil genuinely tests low in phosphorus, it's a sound, inexpensive choice.
Under Sod™, and how it differs
Under Sod™ is built around a different job — not "feed the new lawn broadly," but "give the freshly cut roots what they need in the exact zone they land." That leads to four concrete differences:
- Phosphorus: Under Sod™ is low-P (the 2 in 4-2-5); Scotts Starter is high-P. On adequate-to-high phosphorus soils, low-P is the better match.
- Potassium: Under Sod™ is potassium-forward (the 5) for root establishment and stress tolerance; that's not the emphasis of a traditional starter.
- Biology: Under Sod™ carries living soil biology — mycorrhizae, *Bacillus*, *Trichoderma*, humic and fulvic acid, seaweed — to help roots reach water and nutrients on their own. A synthetic starter feeds; it doesn't inoculate.
- Iron: Under Sod™ is iron-free by design, because the job under new sod is roots first, not blade color.
| Factor | Scotts Turf Builder Starter | Under Sod™ |
|---|---|---|
| Type | Synthetic feed | Biological starter |
| Phosphorus | High | Low (the 2 in 4-2-5) |
| Potassium | Not the emphasis | Potassium-forward (the 5) |
| Soil biology | None — feeds, doesn't inoculate | Mycorrhizae, *Bacillus*, *Trichoderma*, humic/fulvic, seaweed |
| Best fit | Soil that tests low in phosphorus | Adequate-to-high phosphorus soils (most Northeast lawns) |
Which one for your lawn
Test your soil. If phosphorus is low, Scotts Starter (or any high-P starter) is the right, legal choice. If phosphorus is adequate-to-high — most Northeast lawns — a low-P biological starter like Under Sod™ fits new sod better and keeps you clear of phosphorus fertilizer restrictions. Application is simple either way; Under Sod™ is one 25 lb bag per 500 sq ft pallet, raked into the prepared soil before the sod is laid.
Where Under Sod™ fits
Under Sod™ is a 4-2-5, iron-free, potassium-forward biological starter in an SGN 90 granule, made to sit in the soil-to-root contact zone under new sod. See the full product specs or join the notification list for the Fall 2026 Northeast launch.
This is general guidance, not a substitute for a soil test. Competitor formulas vary by product and can change; check the current label, and confirm your local phosphorus rules before applying either product.
Frequently Asked Questions
Is Scotts Turf Builder Starter good for new sod?+
It's a solid high-phosphorus synthetic starter, and it's the right pick when a soil test shows your soil is low in phosphorus. On the adequate-to-high phosphorus soils that describe most Northeast lawns, a low-P biological starter fits new sod better.
What's the difference between Under Sod™ and Scotts Starter?+
Scotts Starter is a high-phosphorus synthetic feed for a new lawn broadly. Under Sod™ is a low-phosphorus, potassium-forward biological starter for the root-contact zone under sod — it adds mycorrhizae and beneficial bacteria and is iron-free by design.
Which is better for new sod?+
It depends on your soil test. Low phosphorus favors a high-P starter like Scotts; adequate-to-high phosphorus (most Northeast lawns) favors a low-P biological starter like Under Sod™.
Can I use Scotts Starter under sod?+
You can. It's built to be broadcast and watered in, though, while Under Sod™ is formulated to be applied to the prepared soil in the root-contact zone before the sod is laid.
Under Sod™ launches Fall 2026
Under Sod™ launches in the Northeast in Fall 2026. 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.