There’s nothing more satisfying than keeping your grass beautifully manicured. A perfect lawn can become an ‘outside room’ in its own right that you can use all year round. So what role can compost play in keeping your lawn healthy?
Compost is very good for grass, and has multiple benefits including improving grass root health, adding nutrients to topsoil, and fighting thatch, weeds and diseases. It’s a natural weed-killer and organic fertilizer.
So let’s dive down into the benefits of compost for grass in more detail, and look at when to add compost to your lawn and how. We’ll also consider how to avoid adding too much compost to your topsoil – which could actually do more harm than good.
The Benefits of Adding Compost To Your Lawn
Compost isn’t just good for flower beds and our planet – it’s good for lawns too.
Everybody loves compost. Compost is “black gold” or “the very essence of life”. Compost soaked in water is “compost tea” and compost spread on your lawn is called “top-dressing”.
Compost is a diverse mix of decomposing materials, like eggshells, vegetable peels and grass clippings. Compost has nutrients and microbes. Good compost is made light and airy by worms and beetles. Compost creates a happy food web in your soil.
Compost helps your grasses’ roots survive winters and come out healthier in the spring. If your grass doesn’t have a healthy root system – too thin – then water with essential nutrients (nitrogen, potassium and phosphorus) won’t hang around long enough for roots to take them in.
Compost helps soil keep nutrients. Compost adds life to the food web in your yard.
Compost improves the quality of your soil. Soil amended with compost can absorb up to 30% more water.
Compost is an airy mixture of decomposed solids. Hard, clayey soil tends to compact so that water drains away before plants can benefit from it. If you find your soil tough to dig in for you – so will your grass. Adding compost to clay soil reduces its density and hardness.
In sandy soil, water and any other fertilizer simply runs away. Adding compost to sandy soil builds it up so it can retain moisture.
Adding decomposed compost to any soil will neutralize the acidity or alkalinity. Neutralization allows grass roots to absorb nutrients better.
Compost fights thatch, which is bad for your lawn. Like a root system that is too thin, a root system that is too thick doesn’t allow those nutrients to get to the roots. Heavily thatched lawns will brown and die.
Compost has microorganisms that reduce thatch and restore a healthier root system.
You may not think you want a lawn crawling with microscopic creepy-crawlies – but you do. Compost is loaded with microorganisms that are healthy for your lawn.
Microorganisms effectively bind your soil’s small particles into larger ones that are less likely to be washed out of your lawn. The binding also creates healthy gaps in the soil.
Weeds and Diseases
Compost is a natural weed-killer and organic fertilizer. When your grass has a healthy root system, it can fight off diseases.
When Should I Put Compost On My Lawn?
Top-dressing your lawn means spreading a thin layer – no more than half an inch – of compost evenly over your lawn.
Experts say to top-dress your lawn either in the late spring or early summer. The second-best time is early fall. Timing is important because, after top-dressing, you should give the lawn 3 to 4 mowings before the summer heat or the fall chill sets in.
Experts recommend choosing a dry spell for top-dressing – it will make the spreading easier.
You shouldn’t top-dress your lawn during the heat of summer. Compost has organic matter that may burn your lawn during high temperatures. Don’t top dress your lawn in winter, during grasses’ dormant phase. You may damage or even kill all your grass.
Some experts caution that too much top-dressing will raise the grade of your lawn. They recommend top-dressing the entire lawn once every two years. Problem areas, like bare patches, can be treated every year.
Can I Mix Grass Seed With Compost?
This gets tricky. The problem is that too much compost – over a 1/4 inch – and the seeds won’t grow. Grass seeds should be planted at a depth of 1/8 inch to 1/4 inch depth. If you can’t be precise with the thickness of the top-dressing – because your lawn has too many hills, valleys and bald spots – then overseed after top-dressing.
For bare spots, where the compost may be thicker, consider overseeding after the top-dressing. After applying the compost, spread the seeds evenly and then gently bury them with the back of a rake. Here’s a video.
If your lawn is flat and even, you may be able to add seed to the compost and apply both together – but not over 1/4 inch thick to give those seedlings the best start. A top-dressing machine may help.
How To Top-Dress Lawns With Compost (Quick Tips)
- Check out your compost: it should be free of weeds, sweet smelling, and cool.
- Keep pets away while you top-dress.
- Mow your lawn down to 1 inch tall.
- Pick up grass cuttings (or mow with a grass catcher).
- Remove thatch and moss from your lawn with a rake or mower.
- Pick up thatch.
- After dethatching, make sure your soil is loose and aerated.
- Dump your compost in piles, like molehills, around your yard.
- Rake the piles into an even 1/2 inch layer (but at least 1/8 inch).
- Brush the back of a rake over the grass to make sure that the top-dressing isn’t laying on top of the grass – grass should be sticking up, not buried. The compost should not be a visible layer.
- Water your lawn gently.
Compost Vs Topsoil (Which is Best For Grass?)
Compost is better for your grass, but a mixture works well too.
Topsoil is the uppermost layer of soil above bedrock and it does contain nutrients. But not as much as compost. Often, topsoil is used to start seeds, but topsoil is heavy and can smother seeds.
Straight compost or amended topsoil will be better for seedlings. A good compromise is amending topsoil with compost. Experts recommend using a mix with 30% compost.
Compost Vs Fertiliser (Which One Wins For Your Lawn?)
Experts say – compost feeds the soil and fertilizer feeds the plant.
Fertilizers can be organic (manure, bone meal) or inorganic (man-made chemicals). Fertilizers are designed to give specific nutrients (nitrogen, phosphorus, and potassium) to plants. They help plants grow faster by supplying those specific nutrients.
Compost has several benefits, but mainly compost boosts root and soil health. When the soil is nutrient-rich, everything grows better. But compost takes time (“cooking” compost can take up to a year), and you need a lot.
So – which is better?
Compost builds soil health, and when the soil is healthy, everything is healthy. The point is – you shouldn’t need fertilizers at all if your soil is healthy. The exception is when you have plants with specific deficiencies (like some houseplants). These plants benefit from a specific fertilizer.
Both fertilizers and compost can be toxic to pets – so keep them away.
What Happens If I Put Too Much Compost On My Grass?
If you put too much compost on grass, you may have to scrape it off. With compost, use too little instead of too much.
Grass can get smothered and die if you put too much compost on it. Sheet mulching is the practice of killing a lawn by covering it with a dense sheet of mulch. Deprived of light, the entire lawn dies. Be sure to stick with the 1/4 inch rule of thumb.
The goal with compost is a healthy, balanced soil. Too many compost nutrients and your grass may grow too fast for healthy microbes to catch up.
Will Certain Types of Compost Harm My Lawn?
Like a good wine, compost needs time to mature. Mature compost should reach temperatures of 120°F to 160°F. It should be dark and crumbly. When the compost has “cooked” enough, it becomes stable and is ready for your lawn.
Mature compost smells sweet, like a forest – if your compost smells nasty, it could harm your lawn. Immature compost smells like ammonia. If you put compost that is still decomposing on your lawn, it will burn it. Also, be careful that your compost isn’t actually hot before you put it on your lawn.
Sometimes bad things can get into compost piles and thrive there. Beware of weed seeds. Make sure there are no dyed materials or building materials, like glass or metal.
Very wet composts will not help your lawn. Wet composts have a high (over 60%) moisture content. They will be hard to spread and are not good for roots. Very dry composts tend to float away.
Some store-bought composts are high in metals. These composts are made from biosolids. Check your local Extension agents for maximum recommended levels.
Other store-bought composts are high in salts, which can damage grasses in hot weather. Again, check with your Extension office for recommendations for your area and your lawn.
Most home-grown compost bins produce a good mix of nutrients that plants will love. Manure-based compost that you buy can add too much phosphorus. Phosphorus moves very slowly through the soil and is not very water-soluble.
Too much phosphorus can result in stunted plant growth in your yard. Too much phosphorus in neighboring ponds and lakes create algae blooms.
In the final analysis, provided you add compost sparingly then it can be extremely good for your grass. It adds a much needed mix of nutrients to the soil that your lawn will love.
So if you have thinning patches on your lawn, then the addition of around 1/4 inch of compost will help improve soil quality and help your grass roots become stronger – meaning your overall lawn will become more lush and healthy.
Just remember to keep those pets out of harm’s way when spreading your compost on the grass – perhaps by cordoning off each patch you have treated. 🙂
Homeowner and property investor Larry Jones founded Take a Yard in 2020 to bring you the very best outdoor living content, based on his years of experience managing outside spaces. Read more >