If you are putting sod down before Under Sod ships, Suståne BOLSTER Granular 4-4-4 is a good product to put under it, and we will say so before anyone else does. BOLSTER is a natural-based 4-4-4 with slow-release nitrogen from compost, four species of arbuscular mycorrhizae, seaweed extract, humic acid, and 3 percent chelated iron, backed by decades of Suståne research, and Suståne’s own guidance says to incorporate it into the soil rather than leave it on the surface. That is the right instinct, and it is the instinct Under Sod was built around.
The two products are not the same thing. Here is where they differ, line by line, using Suståne’s label for their numbers and ours for ours.
The comparison
| Factor | Under Sod 4-2-5 | Suståne BOLSTER Granular 4-4-4 + 3Fe |
|---|---|---|
| Analysis | 4-2-5 | 4-4-4 |
| Phosphorus | 2 percent, sized to the Northeast new-lawn exception, not to load the soil | 4 percent |
| Potassium | 5 percent, potassium-forward for root and stress tolerance | 4 percent |
| Iron | None, by design | 3 percent chelated iron for greening |
| Nitrogen release | Slow-release | 3.2 percent slowly available of 4 percent total, from aerobic compost, per label |
| Mycorrhizae | Four endomycorrhizal species; the guaranteed count will be published on the locked label | Four species: Glomus intraradices, Glomus etunicatum, Glomus deserticola, and Glomus clarum; guaranteed minimum 3.52 propagules per gram |
| Bacteria and fungi beyond mycorrhizae | Bacillus and Trichoderma | Compost-based microorganisms |
| Biostimulants | 6 percent humic acid plus fulvic acid; 2 percent Ascophyllum nodosum seaweed | Humic acid and 1 percent Ascophyllum nodosum seaweed extract |
| Granule | SGN 90 | Fine grade, 100 SGN |
| Built for | The top 4 inches of prepared topsoil directly under transplanted sod, up to 6 where the topsoil lift is deeper | Landscape, pre-plant, soil mixes, seeding, and turf establishment |
| How it is applied | Mixed into the top 4 inches of prepared topsoil before the sod, up to 6 where the lift is deeper — the depth Michigan State and Rutgers publish for fertilizer before sod. | Suståne directs pre-plant users to broadcast and incorporate it into the top 4 inches of soil; follow their label |
| Rate | One 25-pound bag per 500 square feet, one bag per pallet of sod | Per Suståne’s label for the use |
| Buy it today | No. First shipments Spring 2027 through CT Sod, then regional partners; notify list below | Yes, through Suståne dealers |
Factor
Phosphorus
Under Sod 4-2-5
2 percent, sized to the Northeast new-lawn exception, not to load the soil
Suståne BOLSTER Granular 4-4-4 + 3Fe
Factor
Potassium
Under Sod 4-2-5
5 percent, potassium-forward for root and stress tolerance
Suståne BOLSTER Granular 4-4-4 + 3Fe
Factor
Iron
Under Sod 4-2-5
None, by design
Suståne BOLSTER Granular 4-4-4 + 3Fe
Factor
Nitrogen release
Under Sod 4-2-5
Slow-release
Suståne BOLSTER Granular 4-4-4 + 3Fe
3.2 percent slowly available of 4 percent total, from aerobic compost, per label
Factor
Mycorrhizae
Under Sod 4-2-5
Four endomycorrhizal species; the guaranteed count will be published on the locked label
Suståne BOLSTER Granular 4-4-4 + 3Fe
Factor
Bacteria and fungi beyond mycorrhizae
Under Sod 4-2-5
Bacillus and Trichoderma
Suståne BOLSTER Granular 4-4-4 + 3Fe
Factor
Biostimulants
Under Sod 4-2-5
6 percent humic acid plus fulvic acid; 2 percent Ascophyllum nodosum seaweed
Suståne BOLSTER Granular 4-4-4 + 3Fe
Humic acid and 1 percent Ascophyllum nodosum seaweed extract
Factor
Built for
Under Sod 4-2-5
The top 4 inches of prepared topsoil directly under transplanted sod, up to 6 where the topsoil lift is deeper
Suståne BOLSTER Granular 4-4-4 + 3Fe
Landscape, pre-plant, soil mixes, seeding, and turf establishment
Factor
How it is applied
Under Sod 4-2-5
Mixed into the top 4 inches of prepared topsoil before the sod, up to 6 where the lift is deeper — the depth Michigan State and Rutgers publish for fertilizer before sod.
Suståne BOLSTER Granular 4-4-4 + 3Fe
Factor
Rate
Under Sod 4-2-5
One 25-pound bag per 500 square feet, one bag per pallet of sod
Suståne BOLSTER Granular 4-4-4 + 3Fe
Factor
Buy it today
Under Sod 4-2-5
No. First shipments Spring 2027 through CT Sod, then regional partners; notify list below
Suståne BOLSTER Granular 4-4-4 + 3Fe
What the differences mean
Phosphorus. Most Northeast lawn soils already test adequate to high in phosphorus, and Connecticut, New York, New Jersey, and Massachusetts all restrict phosphorus on established lawns while allowing it on new ones. Under Sod carries 2 percent for two reasons: the job is the first season under transplanted turf, not loading a soil that does not need it, and mycorrhizal fungi colonize roots more readily when soil phosphorus is not abundant, so a low-phosphorus carrier gives the inoculant in the same bag a better chance of taking. BOLSTER’s 4 percent is still far below a seed starter’s 18 to 25. BOLSTER carries 4 percent and is built for a wider range of plantings. Both are legal under new sod. A soil test is the thing that tells you which number your dirt actually wants.
Potassium. Under Sod is potassium-forward on purpose: potassium supports rooting and stress tolerance in the establishment window, when new sod is losing water faster than it can take it up. BOLSTER is balanced.
Iron. BOLSTER includes 3 percent chelated iron, which greens turf up fast. Under Sod leaves iron out on purpose. New sod arrives green; what it needs from the soil under it is roots, not color, and iron under sod does nothing for rooting. We root the sod. We do not green the bag.
Biology. Both products carry four species of endomycorrhizae, seaweed, and humic acid. Under Sod adds fulvic acid and named Bacillus and Trichoderma cultures placed at the root zone. Suståne publishes its mycorrhizal count on the label; we will publish ours on ours.
The job. BOLSTER is a landscape establishment product that works under sod. Under Sod is a product for the soil under sod that does not try to be anything else, bagged so that one bag covers one pallet and the crew never does math on a hot driveway.
If you are sodding before Under Sod ships
Use BOLSTER, and use it the way Suståne says to: incorporated into the soil, not spread on top. Skip the high-phosphorus seed starters entirely. Get four to six inches of screened topsoil on the subgrade first, because no bag fixes builder fill. Lay the sod the same day, roll, and water in. One rule if the timing straddles the launch: do not put both products down at full rate on the same soil. Use one or the other under a given section, and switch to Under Sod for the sections that go down after it ships. Then join the list below.
First shipments Spring 2027
First shipments Spring 2027 across the Northeast, one bag per pallet.
Frequently asked questions
Can I use Suståne BOLSTER under sod instead of Under Sod?+
Yes. It is a good product for the job and the closest thing you can buy today. Incorporate it into the soil per Suståne’s label rather than spreading it on the surface.
Is Under Sod the same thing as BOLSTER?+
No. BOLSTER is a balanced 4-4-4 with 3 percent iron built for landscape establishment generally. Under Sod is a 4-2-5, iron-free, potassium-forward product built only for the soil under transplanted sod, bagged one bag per pallet.
Why 4-2-5 instead of 4-4-4?+
Because most Northeast soils do not need more phosphorus and new sod does need potassium. The middle number is sized to the new-lawn exception in the Northeast phosphorus laws, not to the soil’s appetite.
Why no iron?+
Sod arrives green. Iron under it does nothing for rooting, and rooting is the only job in the first season.
Can I use both on the same lawn?+
Not at full rate on the same soil. Use one product under a given section. If part of the lawn goes down before Under Sod ships and part after, BOLSTER under the first sections and Under Sod under the rest is fine.
Which has more mycorrhizae?+
Suståne guarantees a minimum of 3.52 propagules per gram of four species on its label. Under Sod’s count will be on its label; we will not print a number here until it is.
Where do I buy Under Sod?+
Nowhere yet. First shipments are Spring 2027 across the Northeast, through CT Sod first and then regional partners. Join the list above, or call CT Sod at (203) 806-4086 and ask to be put on the first-shipment list.
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 Spring 2027 across the Northeast.