Moss in Your Lawn: Why It's There and How to Get Grass Back

In this guide

1. Why moss shows up
2. Step 1: find your cause
3. Step 2: fix the conditions
4. Step 3: remove the moss
5. Step 4: reseed
6. When to do what
7. Common mistakes to avoid
8. The bottom line

Plenty of Northeast homeowners spend money every spring killing moss, only to watch it come right back by fall. That's because moss isn't really the problem. It's a symptom. Moss doesn't crowd out healthy grass; it fills in the spaces where grass is already failing. Fix whatever is making the grass struggle, and the moss loses its foothold.

Why moss shows up

Moss thrives in conditions that are tough for lawn grass. Most mossy lawns have one or more of these:

The Northeast is a perfect storm for moss: lots of mature shade trees, naturally acidic soils, and cool, damp springs and falls.

Step 1: find your cause

Before buying anything, do these quick checks:

1. Count the sun hours. On a summer day, note when the mossy area gets direct sun. If it's under four hours, shade is your main issue.
2. Get a soil test. It tells you pH and fertility in one go. See our guide to soil pH and lime for how to take a sample.
3. Do the screwdriver test. Push a long screwdriver into moist soil. Struggling to get past 2 inches means compaction.
4. Watch after a heavy rain. Puddles that sit for hours mean a drainage problem.

Most mossy lawns have two or three of these at once, typically shade plus acidity.

Step 2: fix the conditions

More light

• Limb up trees. Removing low branches (up to about 8 to 10 feet) lets in much more angled morning and afternoon light. Thinning the canopy helps too. For large trees, hire a certified arborist.
• Be realistic about deep shade. If an area gets less than about three hours of direct sun, even the most shade-tolerant grass will struggle. A mulched bed, shade-loving groundcover, or simply accepting a moss area can be the smarter choice.

Correct the pH

If your soil test says your pH is low, apply lime at the recommended rate, splitting large amounts between fall and spring. It takes months to work, so be patient. Lime on its own won't kill moss, but it helps grass compete.

Relieve compaction

Core aerate compacted areas in late summer or early fall, ideally right before overseeding.

Fix drainage

For low spots, gradually topdress with a quarter inch of compost or topsoil at a time to raise the grade. For bigger drainage problems, such as downspouts discharging onto the lawn, redirect the water first.

Feed and mow properly

Follow a sensible fertilizer schedule (shaded areas generally need less nitrogen than sunny ones), and mow at 3 to 3.5 inches. Taller grass shades the soil and competes better.

Step 3: remove the moss

Once you've started fixing the conditions, clear the moss so new grass seed can reach the soil.

• Rake it out. A firm metal leaf rake or a dethatching rake pulls up most moss easily, especially when it's moist. For large areas, a rented power rake (dethatcher) speeds things up.
• Moss control products. Products based on iron sulfate or potassium salts of fatty acids (often sold as moss killers) turn moss brown or black within days, making it easier to rake out. They don't prevent moss from returning unless you also fix the conditions. Follow the label carefully; iron products can stain concrete, stone and clothing.

Rake out the dead moss a week or two after treating.

Step 4: reseed

Bare soil left after removing moss will just grow more moss or weeds if you leave it. Overseed right away:

• Best time: late August through September, when soil is warm and nights are cool. See the fall seeding guide.
• Second choice: early spring, or dormant seeding in late fall.
• Loosen the top quarter inch of soil, spread seed, rake lightly so seed contacts soil, and keep it consistently moist until it's established.

When to do what

Common mistakes to avoid

• Killing moss without changing anything. It'll be back within a season.
• Seeding sun-loving grass in shade. A bluegrass-heavy mix under a maple won't last.
• Liming without a soil test. Not every mossy lawn is acidic.
• Leaving leaves on shaded areas in fall. They smother thin grass and keep the soil damp all winter.
• Fighting a battle you can't win. In very deep shade, a bed or groundcover is a reasonable answer.

The bottom line

Treat moss as a messenger. It's telling you the grass in that spot is short on light, has the wrong pH, compacted soil or too much water. Fix the condition, rake out the moss, and reseed with the right grass, and the moss won't come back.

For what to do this month, see the lawn calendar.

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