Best Fertilizers for Spring Lawns

Spring fertilization is one of the most impactful things you can do for your lawn — but it’s also one of the easiest to screw up. Apply too early and you get lush top growth with weak roots. Apply too much and you risk burning the lawn or creating a thatch problem. Apply the wrong type and you’re wasting money.

This guide covers what to use, when to apply it, and how much — with specific product recommendations for every situation.

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Spring Fertilizer Basics

What the Numbers Mean

Every fertilizer bag has three numbers — like 24-0-11 or 10-10-10. These represent:

• N (Nitrogen): Drives leaf and blade growth. Makes grass green.
• P (Phosphorus): Supports root development and seedling establishment.
• K (Potassium): Builds overall plant health, disease resistance, and stress tolerance.

For established lawns in spring, you generally want higher nitrogen, low or no phosphorus, and moderate potassium. Phosphorus is usually only needed for new seeding or if a soil test shows a deficiency. Many states actually restrict phosphorus in lawn fertilizers because excess phosphorus runs off into waterways.

Slow-Release vs. Quick-Release

Slow-release nitrogen breaks down gradually over 6–12 weeks, feeding your lawn consistently without surge growth. This is what you want for spring fertilization. It’s harder to over-apply, produces steady growth, and requires less frequent mowing.

Quick-release nitrogen is immediately available to the plant. It greens up the lawn fast but causes a growth surge followed by a crash. It’s useful for spot fixes but not ideal as your primary spring fertilizer.

Look at the fertilizer label for “slowly available nitrogen” or “water-insoluble nitrogen” (WIN). A good spring fertilizer should have at least 30–50% of its nitrogen in slow-release form.

When to Apply

Cool-season grasses: Mid-to-late spring (when the grass has been actively growing for 2–3 weeks). For most northern lawns, that’s late April through mid-May. Don’t fertilize too early — early spring nitrogen pushes blade growth at the expense of root development.

Warm-season grasses: Wait until full green-up, which is usually late April through May depending on your location. Fertilizing dormant or semi-dormant warm-season grass doesn’t help and can promote weed growth.

The soil test rule: A $15 soil test from your local extension office tells you exactly what your lawn needs. It removes all guesswork and often saves you money by showing you which nutrients you don’t need to add.

Our Top Picks

Best Overall: Milorganite 6-4-0

Milorganite is the lawn care community’s not-so-secret weapon. It’s an organic, slow-release fertilizer made from heat-dried microbes — specifically, the byproduct of Milwaukee’s wastewater treatment process. That might sound unusual, but the results speak for themselves.

NPK: 6-4-0 (with 2.5% iron)

What we like:

• Nearly impossible to burn your lawn — the slow-release organic nitrogen feeds gently over 8–10 weeks
• Added iron promotes deep green color without excessive growth
• Improves soil biology over time — feeds the microorganisms that make soil healthy
• No salt buildup (a common problem with synthetic fertilizers)
• Safe around kids, pets, and waterways after application
• Works great on both cool-season and warm-season grasses
• Available everywhere — big box stores, garden centers, even Amazon

What we don’t:

• Lower nitrogen content means you need more product per application (about 32 lbs per 2,500 sq ft)
• Has a distinctive smell for 24–48 hours after application
• Doesn’t green up the lawn as quickly as synthetic fertilizers
• Contains phosphorus, which may not be allowed in your area for established lawns

Application rate: 32 lbs per 2,500 sq ft, 4 times per year (Memorial Day, July 4th, Labor Day, Thanksgiving for cool-season lawns)

Best for: Homeowners who want a simple, reliable fertilizer that’s hard to mess up. The “apply it and forget it” choice.

Best Synthetic: Scotts Turf Builder Triple Action

If you want an all-in-one product that fertilizes, kills weeds, and prevents crabgrass in a single application, Scotts Triple Action is hard to beat. It’s engineered for spring specifically.

NPK: 29-0-10

What we like:

• Three products in one: spring fertilizer + pre-emergent (crabgrass preventer) + post-emergent (kills existing broadleaf weeds like dandelions and clover)
• Higher nitrogen content means less product per application
• Includes potassium for stress tolerance heading into summer
• No phosphorus — compliant with phosphorus restrictions
• Well-established product with consistent results
• Time-saving — one pass with the spreader handles three tasks

What we don’t:

• Cannot be used on newly seeded areas — the pre-emergent prevents grass seed germination too
• Contains chemicals that some homeowners prefer to avoid
• More expensive per application than basic fertilizer
• Quick-release nitrogen component can cause surge growth
• Doesn’t work on warm-season grasses that haven’t fully greened up

Application rate: Follow bag directions — typically about 3–4 lbs per 1,000 sq ft. Apply with a broadcast spreader for even coverage.

Best for: Cool-season lawn owners who want maximum efficiency — fertilize, prevent crabgrass, and kill existing weeds in one pass. Especially good if crabgrass was a problem last year.

Best for New Lawns: Scotts Starter Lawn Food (24-25-4)

Starting a new lawn from seed or sod? You need phosphorus for root establishment, and this is the best option for the job.

NPK: 24-25-4

What we like:

• High phosphorus content specifically designed for root development in new grass
• Works for both seed and sod establishment
• Also includes a pre-emergent for weed prevention that won’t inhibit grass seed germination (mesotrione-based)
• Balanced nitrogen for early blade growth without overwhelming new roots
• Clear application instructions on the bag

What we don’t:

• Not for established lawns — the high phosphorus isn’t needed and may violate local restrictions
• More expensive than standard fertilizer
• Only needed for the first 1–2 applications on new grass

Application rate: Per bag directions, typically applied at seeding and again 4–6 weeks later.

Best for: Anyone planting new grass seed, overseeding, or laying sod. This is a specialty product for establishment — switch to a regular fertilizer after the lawn matures.

Best Organic: Espoma Organic Lawn Food (9-0-0)

For homeowners committed to organic lawn care, Espoma makes the most widely available and consistently effective organic fertilizer.

NPK: 9-0-0 (with calcium, sulfur, and iron)

What we like:

• 100% organic, made from feather meal, pasteurized poultry manure, and gypsum
• All slow-release — feeds over 8–12 weeks with no burn risk
• Includes calcium and sulfur that improve soil structure
• Added iron for deep green color
• No synthetic chemicals — safe for organic programs
• Won’t leach or run off as readily as synthetics

What we don’t:

• Lower nitrogen content means more frequent applications or more product
• Smell after application (less than Milorganite but still noticeable)
• No potassium — you may need a separate application based on soil test
• Can be harder to find in some areas (Amazon is your best bet)

Application rate: About 8 lbs per 1,000 sq ft, applied every 8 weeks during the growing season.

Best for: Organic lawn care enthusiasts who want a pure, no-compromise product. Pairs well with compost top-dressing for a fully organic program.

Best Budget: Pennington UltraGreen Lawn Fertilizer (30-0-4)

When you need solid results without breaking the bank, Pennington UltraGreen delivers impressive performance for its price point.

NPK: 30-0-4

What we like:

• Excellent price per square foot of coverage — often $15–$20 for 5,000 sq ft
• 30% nitrogen with a blend of quick-release (for fast green-up) and slow-release (for sustained feeding)
• Includes iron for enhanced color
• Added potassium for disease resistance
• No phosphorus — meets environmental guidelines

What we don’t:

• Higher percentage of quick-release nitrogen means more growth surge than premium options
• Needs careful application — easier to burn at higher rates
• Less slow-release nitrogen than more expensive options
• Bags can be hard to reseal after opening

Application rate: About 3.3 lbs per 1,000 sq ft per the label.

Best for: Budget-conscious homeowners who want a good-looking lawn without spending $40+ per bag. A solid everyday fertilizer that gets the job done.

Application Tips

Getting the product right is only half the equation. Here’s how to apply it correctly:

Use a Broadcast Spreader

Drop spreaders leave visible lines. Broadcast (rotary) spreaders distribute fertilizer evenly in an overlapping pattern. For most homeowners, a broadcast spreader is the better tool.

Calibrate your spreader before each use. The spreader setting on the fertilizer bag is a starting point, but spreaders vary. Test on a driveway or tarp first if you’re unsure.

Apply in Two Passes

For the most even coverage, set your spreader to half the recommended rate and make two passes — one in a north-south direction and one east-west. This crosshatch pattern eliminates striping.

Water After Application

Most granular fertilizers need water to activate. Apply fertilizer and then water the lawn with about ¼ inch of irrigation, or time your application before a forecasted rain (not a downpour, which can wash product away).

Don’t Fertilize Stressed Grass

If your lawn is drought-stressed, dormant, or disease-ridden, don’t add fertilizer. Fix the underlying problem first. Fertilizing stressed grass is like giving a sick person a treadmill — it makes things worse.

Stay Off Hard Surfaces

Sweep or blow any fertilizer that lands on driveways, sidewalks, or patios back onto the lawn. Fertilizer on hard surfaces washes into storm drains and waterways.

Spring Fertilizer Schedule

Here’s a simple schedule for your first year. Adjust based on soil test results and your grass’s response.

Cool-Season Lawns (Kentucky Bluegrass, Fescue, Ryegrass)

Note: Fall fertilization is actually more important than spring for cool-season grasses. The September application fuels root growth and carbohydrate storage that carry the lawn through winter.

Warm-Season Lawns (Bermuda, Zoysia, St. Augustine, Centipede)

Note: Centipede grass needs only 1–2 fertilizer applications per year total. Over-fertilizing centipede causes decline. Less is truly more.

How Much to Apply

The standard recommendation for most established lawns is 1 pound of actual nitrogen per 1,000 square feet per application. Here’s what that means in practice:

• Milorganite (6-4-0): 16.7 lbs of product per 1,000 sq ft = 1 lb of nitrogen
• Scotts Triple Action (29-0-10): 3.4 lbs of product per 1,000 sq ft = 1 lb of nitrogen
• Pennington UltraGreen (30-0-4): 3.3 lbs of product per 1,000 sq ft = 1 lb of nitrogen

To calculate for any fertilizer: divide 100 by the first number (nitrogen percentage). That gives you the pounds of product needed per 1,000 sq ft to deliver 1 lb of nitrogen.

Example: A 24-0-11 fertilizer → 100 ÷ 24 = 4.2 lbs of product per 1,000 sq ft.

Frequently Asked Questions

Can I use the same fertilizer on warm-season and cool-season grasses?

Yes, for the most part. The timing differs, but a balanced slow-release fertilizer works on any grass type. The exception is specialty products like Scotts Triple Action, which is formulated specifically for cool-season lawns.

Should I fertilize if I didn’t do a soil test?

You can, but you’re guessing. A soil test costs $15 and removes all uncertainty. That said, if you’re using a general-purpose slow-release fertilizer (like Milorganite), you’re unlikely to cause harm.

What if I apply too much?

If you’ve over-applied, water the area heavily and immediately to dilute the fertilizer and push it into the soil. For synthetic fertilizers, over-application can burn the lawn — you’ll see yellow or brown streaks within a few days. Organic and slow-release products are much more forgiving.

Is liquid fertilizer better than granular?

Neither is objectively better. Liquid is absorbed faster (good for quick fixes), while granular is easier to apply evenly and lasts longer. For regular spring fertilization, granular is more practical for most homeowners.

Do I still need to fertilize if I leave grass clippings on the lawn?

Yes, but you may need less. Grass clippings return about 25% of the nitrogen you apply back to the soil. Grasscycling (leaving clippings) effectively gives you one free fertilizer application per year.

The Bottom Line

Spring fertilization doesn’t have to be complicated. Here’s the simple version:

1. Get a soil test ($15, done once every 2–3 years)
2. Pick a slow-release fertilizer from our recommendations above
3. Apply in mid-to-late spring when grass is actively growing
4. Use a broadcast spreader in a crosshatch pattern
5. Water it in after application
6. Don’t overdo it — follow the label rates

Your lawn will respond. Within 2–3 weeks of a well-timed spring application, you’ll see thicker, greener growth that lasts for weeks. Pair this with proper mowing height and the rest of our spring checklist, and you’ll have the best-looking lawn on the block.