Quick answer
Milorganite is a slow-release organic nitrogen fertilizer with iron that greens up an established lawn; Under Sod™ is an iron-free, potassium-forward biological starter made for the soil beneath new sod. For a new install, you want root establishment over blade color — which is exactly why Under Sod™ leaves the iron out and leads with potassium and soil biology. Milorganite is better suited to feeding and greening a lawn that's already rooted.
Milorganite, fairly
Milorganite is a genuinely good product for what it's for: a slow-release organic nitrogen source that also supplies iron, which is why it's a favorite for deepening the color of an established lawn without a nitrogen surge. Gardeners reach for it because it's forgiving, organic, and hard to burn a lawn with. Nothing here is a knock on Milorganite.
Why it isn't purpose-built for under new sod
The mismatch is about the job, not quality:
- Iron: Milorganite's iron is a feature for greening established turf — but under new sod, forcing blade color before the roots are ready is the opposite of the goal. Under Sod™ is iron-free on purpose.
- Potassium: Milorganite carries little to no potassium; Under Sod™ leads with it (the 5 in 4-2-5) precisely because potassium supports root establishment and stress tolerance in a new lawn.
- Placement and biology: Milorganite is a broadcast feed for turf that's already rooted. Under Sod™ is formulated to sit in the soil-to-root contact zone, applied before the sod is laid, and it includes the mycorrhizae and beneficial bacteria that help cut roots bridge into native soil.
| Factor | Milorganite | Under Sod™ |
|---|---|---|
| Primary job | Feed & green an established lawn | Root new sod at the soil interface |
| Nitrogen | Slow-release organic N | Modest, slow-release (the 4 in 4-2-5) |
| Potassium | Little to none | Potassium-forward (the 5) |
| Iron | Contains iron (for color) | Iron-free by design |
| Soil biology | Not a biological inoculant | Mycorrhizae, *Bacillus*, *Trichoderma*, humic/fulvic, seaweed |
| Placement | Broadcast on rooted turf | On soil, sod laid on top |
The honest take
If you're feeding an established lawn and want slow-release nitrogen with a color boost, Milorganite is a reasonable pick. If you're installing new sod and want to prioritize fast, deep rooting in the first month, a low-P, iron-free, potassium-forward biological starter fits the job better. Under Sod™ is that: one 25 lb bag per 500 sq ft pallet, raked into the prepared soil before the sod goes down, watered in after.
Where Under Sod™ fits
Under Sod™ is a 4-2-5, iron-free, potassium-forward biological starter in an SGN 90 granule, with mycorrhizae, *Bacillus* and *Trichoderma*, humic and fulvic acid, and seaweed extract — made for the root-contact zone under new sod. See the full product specs or join the notification list for the Fall 2026 Northeast launch.
Frequently Asked Questions
Can I use Milorganite under new sod?+
You can, but it's built to feed and green an established lawn — slow-release nitrogen and iron, with little to no potassium. Under new sod, a low-phosphorus, iron-free, potassium-forward biological starter fits the job better.
Does Milorganite have potassium?+
Little to none. Under Sod™ leads with potassium (the 5 in 4-2-5) precisely because potassium supports root establishment and stress tolerance in a new lawn.
Why is Under Sod™ iron-free when Milorganite contains iron?+
Iron greens the blade, which is a feature for established turf. Under new sod the goal is roots first, not top color, so Under Sod™ leaves the iron out on purpose.
Is Milorganite a starter fertilizer for sod?+
It's a slow-release nitrogen feed for established lawns, not a starter placed in the root-contact zone under new sod. For that job, Under Sod™ is built to sit at the soil-to-root interface 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.