Composting Grass Clippings

If you mow a lawn, you have a fantastic resource right at your feet. Composting grass clippings is a simple and effective method to turn that green waste into garden gold. It keeps bags of clippings out of landfills and gives you a free, nutrient-rich soil amendment. This guide will show you exactly how to do it right, avoiding common pitfalls like slimy, smelly piles.

Grass clippings are often called a “green” compost material. This means they are rich in nitrogen, which heats up the compost pile and feeds the microbes that do the decomposing work. However, because they are so dense and wet, they can easily mat down. When they mat, air can’t get in, and you end up with a smelly, anaerobic mess. The key to success is balancing them with “browns.”

Why You Should Never Throw Grass Clippings Away

Bagging up clippings and putting them on the curb is a waste of a valuable resource. Here’s what you gain by composting them instead:

Free Fertilizer: Finished compost adds vital nutrients and organic matter to your garden soil.
Waste Reduction: You significantly cut down your household’s contribution to municipal yard waste streams.
Soil Health: Compost improves soil structure, helping it retain moisture and allowing roots to breathe.
Lawn Health: Leaving some short clippings on the lawn (grasscycling) returns nitrogen directly back to the turf.

What You Need to Get Started

You don’t need fancy equipment. The basics are simple:

Grass Clippings: Your primary “green” material.
Brown Materials: Dry leaves, shredded cardboard, straw, or small wood chips. These add carbon and create air pockets.
A Compost Bin or Pile: A simple heap in a corner works. A bin or tumbler can look tidier and may speed up the process.
A Garden Fork or Pitchfork: For turning and aerating the pile.
Water Source: A hose or watering can to keep the pile moist.

The Perfect Ratio: Greens to Browns

This is the most important step to avoid a slimy pile. A good rule of thumb is to aim for a mix of about 1 part green to 2 or 3 parts brown by volume. Since grass is very wet and high in nitrogen, err on the side of more browns.

When you add a bucket of fresh grass clippings, add two or three buckets of dry, shredded leaves or cardboard. If your pile starts to smell like ammonia or rotten eggs, add more browns immediately and turn it to get air in.

Great Brown Materials to Mix With Grass

Dry, fallen leaves (shredded is best)
Shredded paper or cardboard (no glossy inks)
Straw or hay
Sawdust from untreated wood
Small twigs (they help with aeration)

Step-by-Step: Building Your Grass Clipping Compost Pile

Follow these numbered steps for a foolproof start.

Choose Your Spot: Pick a level, well-draining area in partial sun if possible.
Start with a Brown Base: Lay down a few inches of coarse browns like twigs or straw. This helps with drainage and airflow from the bottom.
Add Layers: Add a 2-3 inch layer of fresh grass clippings. Immediately top it with a 4-6 inch layer of browns. Think of it like making lasagna: green layer, brown layer, repeat.
Moisten as You Go: Each layer should be as damp as a wrung-out sponge. Lightly water dry brown materials before adding them.
Continue to Build: Keep adding layers until your bin is full or your pile is about 3 feet high. This size helps it heat up properly.
Cover if Needed: In very rainy climates, a loose cover (like a tarp) can prevent the pile from getting waterlogged.

Maintaining Your Compost Pile

Once built, your pile needs a little care to decompose quickly.

Turning: After a week or so, the center should feel warm. This is a good time to turn the pile. Use your fork to move material from the outside to the inside. This adds oxygen, which is crucial for fast composting. Turn it every week or two if you can.

Monitoring Moisture: Squeeze a handful of compost. If a few drops of water come out, it’s perfect. If it’s soggy, add more browns and turn it. If it’s dry, give it a light watering.

Common Problems and Simple Solutions

Even with the best intentions, things can go a little off track. Here’s how to fix common issues.

Problem: Pile is Slimy and Smells Bad

Cause: Too many greens, not enough air. The grass has matted down.
Fix: Turn the pile immediately to incorporate air. Mix in a generous amount of dry brown material like straw or shredded paper.

Problem: Pile is Not Heating Up

Cause: It could be too dry, too small, or lack nitrogen.
Fix: Check moisture first. If dry, water it. If it’s small, add more material. If it seems balanced but cold, add a fresh batch of grass clippings or another green like vegetable scraps.

Problem: Attracting Flies or Pests

Cause: Food scraps or meat/dairy in the pile, or the pile is too wet.
Fix: Avoid adding kitchen scraps other than fruit/veggie peels. Bury any food waste deep in the center. Ensure your brown-to-green ratio is correct and cover the pile with a layer of browns or a burlap sack.

When is the Compost Finished?

Finished compost is dark, crumbly, and smells like fresh earth. You shouldn’t be able to recognize the original grass or leaves. This process can take anywhere from two months to a year, depending on how often you turn it and the balance of materials.

You can sift it through a screen to get a fine product for potting mixes, or use the chunkier stuff as a mulch around trees and shrubs. It’s ready when it looks and smells like soil.

An Even Easier Method: The “Lazy” Compost Pile

If you don’t want to turn a pile regularly, you can still compost grass. Simply mix your clippings with a huge amount of browns—like a 1:4 ratio—and build a large pile. Let it sit. It will decompose slowly over 6-12 months without any turning. Just be patient, and you’ll still get great compost.

What About Herbicides and Weed Seeds?

This is a important consideration. Avoid composting clippings from lawns treated with broad-leaf herbicides (weed killers) within the last few mowings, as some can persist and harm your garden plants. If you have a lot of weeds that have gone to seed in your lawn, the heat of a well-maintained, hot compost pile should kill most seeds, but a cold, slow pile may not.

FAQ: Quick Answers to Common Questions

Can I compost grass clippings on there own?
It’s not recommended. They will likely form a smelly, anaerobic mat. Always mix them with browns.

How long does it take to compost grass clippings?
In a well-managed, hot compost pile, grass clippings can break down in a few weeks. In a slower, cold pile, it may take several months.

Are grass clippings good for compost?
Yes, they are an excellent source of nitrogen, a crucial component for heating up your compost pile and creating finished compost quickly.

Should I leave clippings on the lawn or compost them?
Both are excellent options. Leaving short clippings on the lawn (grasscycling) feeds the grass. Composting them is better if your grass is very long, you have a disease issue, or you want the compost for garden beds.

Can I add diseased grass to the compost?
It’s safer not to. While a hot pile (over 140°F) may kill pathogens, a home pile often doesn’t get consistently hot enough. To avoid spreading lawn disease, it’s best to bag and dispose of diseased clippings.

Starting a compost pile with your grass clippings is one of the smartest moves a gardener can make. It closes the loop in your yard’s ecosystem, saving you money and creating healthier soil. By following the simple layering technique and maintaining the right balance, you’ll never see those clippings as waste again. Instead, you’ll see them as the first step toward a more vibrant garden.