Quick answer
Under Sod is mixed into the top 4 inches of prepared topsoil before the sod goes down, up to 6 where the topsoil lift is deeper. One 25-pound bag covers 500 square feet, which is one standard pallet of sod: one bag per pallet, no measuring. It is applied once. It is not a surface starter, it is not raked into the top inch, and it is not reapplied after installation.
Before: the starter goes in the soil
The reason is placement. Sod roots are cut at harvest, and they establish into the prepared soil beneath them. Mixing Under Sod through the top 4 inches of prepared topsoil, up to 6 where the topsoil lift is deeper, puts its nutrients and biology throughout the soil the sod will root into during its first season.
Where Under Sod™ fits
Under Sod™ is designed for exactly this step: a 4-2-5 iron-free biological starter applied to the prepared soil before the sod goes down — with named endomycorrhizae, a *Bacillus* and *Trichoderma* biology package, seaweed, and humic acid (plus fulvic acid) — at one 25 lb bag per 500 sq ft pallet, watered in after installation. See the full product specs.
After: only water, then a maintenance feeding at ~30 days
Right after laying sod, the job is water — deep and frequent enough to keep the sod and the soil beneath it consistently moist while the roots knit in. You don't fertilize on top of brand-new sod. Dry fertilizer sitting on the blades can burn the tissue, and the roots aren't developed enough yet to use a surface feeding well. The first maintenance fertilizer comes about 30 days after installation, applied at the labeled rate (not heavier) and watered in thoroughly.
Timing follows standard university turf-extension guidance for cool-season establishment; adjust for your grass type and season.
The full sequence
- Test soil, then grade and prepare.
- Before laying: spread Under Sod over the prepared topsoil and mix it into the top 4 inches with a tiller, harrow, or power rake, up to 6 inches where the topsoil lift is deeper.
- Lay sod, then water in thoroughly.
- Keep watering through establishment (first 2–6 weeks).
- About 30 days after: first maintenance feeding at the labeled rate, watered in.
Frequently Asked Questions
Do you put fertilizer down before or after laying sod?+
Before. Mix Under Sod into the top 4 inches of prepared topsoil before sod is laid, up to 6 where the topsoil lift is deeper. Apply it once. After install, leave the lawn alone for a month, then feed once at one month, then follow the seasonal schedule for your grass and region.
Can you fertilize on top of new sod right after laying it?+
No. Dry fertilizer on the blades can burn the tissue, and the roots aren't developed enough to use a surface feeding well. Right after laying, the job is water — the first maintenance feeding waits about 30 days.
When is the first feeding after installation?+
About 30 days after the sod is laid, once it has begun to root, applied at the labeled rate (not heavier) and watered in thoroughly.
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.