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Clay soil can be a real challenge due to its tendency to dry out and crack. Fortunately, it also has a high capacity to hold nutrients and can actually offer benefits for grass when properly prepared. I’ve dealt with this type of soil for years and have learned that there are fundamental keys to successfully growing grass in it.
To prepare clay soil for grass, incorporate organic material into the soil. Gather material such as organic fertilizer, compost, lawn clippings, and leaves. Mix it into the first 4 to 6 inches and cover with quality topsoil before seeding.
There are plenty of forms of organic material you can use. What’s best will depend on what’s accessible and affordable for you. Once you review the list of options below, we will get into spreading the organic material properly and how and when to check your soil’s progress.
Note: This article is meant to be a quick reference point of key principles but we have a much more complete guide to improving clay soil for new or existing lawns.
What Can I Use for Organic Material?
To prepare your clay soil to plant your grass, you will need to collect organic material and apply it to the soil. Organic material can be “almost anything carbon or nitrogen-based that will biotically deteriorate/degrade over time,” but what type of organic material makes the most sense for you?
Source: Growing a Beautiful Lawn on Clay Soil by FertiLawn
Just a few types of organic material to prepare clay soil for grass include:
- Grass clippings
- Leaves
- Organic fertilizer
- Compost
- Manure
Let’s dive a little further into your options.
| What To Use | Why it Works | Other Notes |
| Grass clippings If you have access to an existing lawn, collecting grass clippings and spreading over the bare soil is an excellent way to prepare it for grass. | Clippings promote retention of soil moisture. As a bonus, grass also contains nitrogen and potassium. | Avoid using chemical-treated grass to improve the quality of your clay soil. This step is only useful if you have an established lawn to collect grass clippings from. |
| Leaves Bag your leaves and spread them on your soil. | Leaves will lighten up your clay soil and help it retain moisture! They also allow beneficial microbes to thrive. | A mixture of green and brown leaves will help to accelerate the decomposition. See How Compost Is Made: The Definitive Guide. |
| Starter Fertilizer Purchase online or in the garden section in your local store. Read the instructions on your fertilizer to determine how much to use, then fill your fertilizer spreader accordingly. | Starter fertilizers are high in phosphorous and can help when establishing a new lawn (source). | Looking for starter fertilizers you can buy online? Scotts Starter Fertilizer is safe for any type of grass and can be used with seed, sod, or plugs. |
| Compost Technically, this is considered organic matter as it has already decomposed. Add around ¼ inch of compost or a 50/50 mix all over your lawn. | Compost promotes drainage and ensures moist soil. It’s like a slow-release fertilizer and soil all rolled into one. | Compost also invites worms to your clay soil. Click here to read our articles on getting started composting at home. |
| Manure It is generally recommended to use a 50/50 blend with manure and compost to reduce the chance of burning the grass. | Manure is useful for compacted soils like clay because it both improves moisture levels and loosens the soil. | You can buy premixed compost and manure from Amazon. |
Applying Organic Material to Clay Soil
Ready to transform that stubborn clay soil? It’s time to apply your organic material!
Topsoil is generally considered to be the top 6 inches of your soil but clay is not topsoil (more on that below). Still, we need to improve this. You will want to mix your organic material with at least the top 6 inches of soil, up to 12 inches would be great because it will help with the drainage as well.
To improve the quality of your clay soil before planting your grass:
- Gather about 6-8 inches of organic material
- Use a tiller to combine the organic material with the clay soil, taking time to go over the area several times to really aggregate deep into the ground. You want an abundance of this organic material mixed into the clay.
Adding Topsoil
Mixing organic material into the clay before seeding will make a significant improvement in the quality of the soil overall but you should still cover the area with an inch or two of quality topsoil if you have access to it. This will give the grass seed an initial starting environment. As the grass takes root, the organic material below will be decomposing, improving the quality of the clay soil below.
These two approaches can really work synergistically together. I made the mistake of spreading topsoil over clay in part of my yard without amending it first. Now, I’m in the process of improving the clay soil under my lawn. You can avoid this by mixing plenty of organic material into the clay first then covered with topsoil and seeding. I really don’t want you to repeat my mistakes.
Ensure the Success of your Clay Soil Prep
Be aware that amending your soil is a long process. It might take some TLC, but consistency pays huge dividends when you are growing a new lawn in this type of soil.
Here are a few more things you can do to ensure you get the best results from your clay soil.
- Obtain a soil test. This will tell you what nutrients are lacking.
- Keep your soil moist: Make sure your clay soil doesn’t dry out completely. Make an effort to keep it moist. If you have an existing lawn, keep your grass damp throughout the summer – you don’t want that soil drying out below. Note: You don’t want to oversaturate clay soil. That will not help. Remember, moderation is key.
- Never use sand as your organic material: Sand will only serve to make your clay soil more concrete. I’ve seen people try to debunk this as a myth. I’ve tried myself. Unfortunately, sand and clay do not mix well at all. I have found no benefit to it.
- Aerate your lawn. I can’t stress enough how beneficial this can be. You’ll probably need to wait a couple of seasons until your grass seeds are thriving and well-rooted but there is a real benefit in core aeration when it comes to clay soil.
How do I Know if My Clay Soil is Improving?
There are a few ways to test the soil the next season. Of course, the most precise method is to use a soil test that you send off for results from a laboratory but if you are looking for a quick and dirty DIY solution, these approaches may help.
Note: These methods were found on The Compost Gardener website. I recommend reviewing their page for the complete step by step process.
The Jar Method
- Collect a handful of the soil and remove any lumps, rocks, roots, etc.
- Place soil in a jar and fill it with water 1/4 to 1/2 full.
- Tighten the lid, and give it a good shake for a couple of minutes.
- Let it sit for at least two days. You’ll see it divide out into layers.
The ideal soil is about 45% mineral (sand, silt, and clay), 5% organic material, 25% water and 25% air according to Lumen’s online Boundless Biology coursebook.
That’s the “textbook instructions” on how to do this but watch this YouTuber give a much simpler explanation and demonstration of how this works:
If you want to learn more about your soil based on the jar method, the USDA texture triangle chart will help you determine what type of soil you are looking at.
The Ribbon Method
- Take a handful of soil from 3-4 inches below the surface
- Spread your oil onto a piece of paper
- Remove lumps, rocks, roots, etc. (you may want to use a kitchen spatula to crush lumps)
- Take a handful of the even soil and get it a little bit wet
- When it reaches the consistency of moist putty, form the soil into a ball
- Gently squeeze your ball of soil with your thumb and forefinger, pushing it out of your hand
If your organic material successfully improved your clay soil, you should see a short ribbon emerge as you push the soil out of your hand.
If your ribbon is longer than one inch, there is still too much clay and you will need to spread another layer of an organic compound. As you complete repeat layers of your organic material, keep in mind it doesn’t have to be as deep as the first once! Your soil is improving and your job is becoming easier.
For a better understanding of this process, watch this YouTube video where the presenter explains how to identify the soil type by its texture and the ribbon test.
Conclusion
I’ve tested multiple strategies for preparing clay soil for grass. This is the approach that I’m currently using and would recommend. It is so important to take the time to really infuse those top several inches of clay with organic material. Compost is excellent but if you don’t have access to it I would not hesitate to use leaves, grass clippings or any other organic material that I could get my hands on.
The more you can break up the clay and allow for aeration and prevent future compacting, the better off your lawn will be.
My final parting advice would be to consider the process of improving clay soil as a journey and not a destination. By that I mean, it takes time. You need to do a little every season to improve the quality and texture of the soil. Your grass with grow healthier and have a stronger root structure if you take the time to improve the soil below it.
Be sure to read Improving Clay Soil For New Or Existing Lawns for more indepth information on what you can do to ensure a healthy soil for your grass.