If you are sowing grass seed for the first time, the best starter fertilizer is The Andersons Premium New Lawn Starter 20-27-5, and the reason is the middle number. Those three numbers on every fertilizer bag are nitrogen, phosphorus and potassium, and phosphorus — the middle one — is what builds roots. New grass has no roots yet, which is the entire problem you are solving, and 27 percent phosphorus is far more than an ordinary lawn feed carries. If you would rather have a gentler feed, the Jonathan Green Green-Up for Seeding & Sodding (12-18-8) is the one to take. If you are seeding a whole lawn rather than a patch, buy the Scotts Turf Builder Starter Food 42 lb bag because the price per pound is far better. And if you are fixing one bare spot, the Scotts Triple Action Built for Seeding is the small, safe, nothing-to-think-about option.
Now the mistake, because it is the one that ruins most first lawns and it is easy to make. Do not put a normal weed-and-feed or a crabgrass preventer on ground where you have just sown seed. Those bags contain a pre-emergent herbicide, and a pre-emergent works by stopping seeds from germinating. It cannot tell the difference between crabgrass seed and the grass seed you paid for. People do this every spring, in good faith, because the bag says “lawn” and it is the season for feeding lawns, and then they wonder why nothing came up. A starter fertilizer is a different product and that is why it exists.
The second thing to know is that a starter fertilizer is a temporaryproduct. You use it when you sow and again about six weeks later, and then you stop. After that, new grass becomes established grass and wants nitrogen rather than phosphorus — a normal 16-4-8 type feed, on the schedule in our lawn fertilizer schedule. Buying a 42 lb bag of starter fertilizer for a lawn you have already established is money spent on the wrong nutrient.
One legal note worth checking before you buy: several US states and municipalities restrict the sale or application of phosphorus lawn fertilizer, because phosphorus runoff feeds algae in lakes and rivers. Starter fertilizer is usually exempt when used for establishing new grass, but the rules are local. A thirty-second search for your state will settle it.
Everything here is ranked on label figures — NPK analysis, stated coverage, bag weight — and we have spread none of it ourselves. See how we pick. Prices are live from the price layer with an “as of” date.
Starter fertilizers compared
| Product | NPK | Size | Coverage | Best for |
|---|
| Andersons New Lawn Starter | 20-27-5 | 18 lb | 5,000 sq ft | Best overall; poor soil |
| Jonathan Green Green-Up Seeding | 12-18-8 | 5,000 sq ft bag | 5,000 sq ft | Gentler feed; seed or sod |
| Scotts Starter Food | Starter analysis | 42 lb | Whole-lawn | Seeding a whole lawn |
| GreenView Starter | Starter + micronutrients | 16 lb | Mid-size lawn | One bag, mid-size lawn |
| Scotts Starter Food (small) | Starter analysis | 3 lb | Patch | Bare-spot repair |
| Scotts Triple Action for Seeding | Seed-safe feed | 4.3 lb | Patch | Simplest beginner option |
NPK analyses, bag weights and coverage figures above are the numbers printed on the labels and published in the listings. Where a label states a coverage area we use it; where it does not, we describe the bag size rather than invent a figure.
Lawn fertilizer starter: what the three numbers mean
Every fertilizer bag carries three numbers, always in the same order, always as a percentage by weight.
The first number is nitrogen (N).It drives leaf growth and green color. It is what an established lawn mostly wants, and on new grass you want a moderate amount rather than a lot — push too much nitrogen and seedlings grow blade they have no root system to support.
The second number is phosphorus (P), and this is the starter number.It drives root development. A normal lawn food runs around 4 percent; a real starter fertilizer runs 18 to 27 percent. This single number is the difference between a starter fertilizer and a bag with “starter” written on it, and it is the one to check before you pay.
The third number is potassium (K). It supports general hardiness and stress tolerance. Useful, rarely decisive on new grass.
So 20-27-5 is a genuine starter analysis: moderate nitrogen, high phosphorus, a little potassium. 12-18-8 is a gentler one — less nitrogen so the seedlings put energy into roots rather than top growth, which is a defensible choice and why it ranks second rather than fourth. Our full explainer on reading a bag and doing the pounds-per-thousand-square-feet arithmetic is in the best lawn fertilizer.
How much do you need, and when do you put it down?
Work in thousands of square feet. Measure your lawn, divide by 1,000, and match that to the coverage on the bag. An 18 lb bag covering 5,000 square feet does a typical suburban front and back; a 3 or 4 lb bag does a patch. Buying by lawn area rather than by bag size is how you avoid both running short halfway through and storing an opened bag that goes solid in a damp garage.
Apply it when you sow, not before and not after.Spread the fertilizer and the seed at the same time — many people do fertilizer first, then seed, then a light rake — so the phosphorus is in the soil where the first roots will reach for it.
Then do it once more, about six weeks later. This is the step beginners skip. The first feed gets the seed up; the second one carries the young grass through establishing a real root system. After that, switch to a normal lawn food.
Use a spreader, not your hands. Hand-scattering gives you dark green stripes where you were generous and thin patches where you were not, and on new grass it shows for a year. A cheap handheld spreader is enough for a patch; for a lawn, see the spreader roundup.
Which bag is right for which job
Seeding a whole lawn from bare soil: the Andersons 20-27-5 if the soil is poor or compacted and you want maximum root drive, or the Scotts 42 lb bag if you want the best price per pound and a product that is in stock everywhere.
Overseeding an existing thin lawn: the Jonathan Green 12-18-8. Lower nitrogen suits seedlings coming up among established grass that is already competing with them for light.
Laying sod rather than sowing seed:the Jonathan Green bag again — it is the one that states sodding as well as seeding on the label.
One bare patch: the 3 lb Scotts starter, or the Triple Action for Seeding if you want weed suppression that will not kill your seed. Do not buy a 42 lb bag for a patch.
A mid-size lawn and one trip: the GreenView 16 lb bag, which also carries micronutrients that thin new topsoil often lacks.
What a starter fertilizer will not do
It will not control weeds, and a new lawn will get them — that is normal, and the answer is to mow rather than to spray, because most herbicides are unsafe on grass under about two months old. It will not fix compacted soil, which is a job for aeration before you sow rather than fertilizer after. And it will not rescue the wrong seed for your region: species choice outlasts every other decision you make here, and it is covered in the best grass seed and fescue grass seed.
Or buy it already mixed with the seed
Everything above assumes you are buying seed and starter feed as two bags, which on a whole lawn is both cheaper and better seed. For a patch or a small area, the seed-and-feed combination bags are ranked in best grass seed and fertilizer combo — with the arithmetic on where the convenience stops being worth it.
