For many property owners, a grass lawn is non-negotiable. But cultivating lush, green grass isn’t as easy as it looks if your growing conditions are less than perfect.
One of the most common obstacles standing in the way of a picturesque lawn is soil composition. In many regions, the soil contains far more clay than is ideal for plant growth. Fortunately, growing grass on clay soil is far from impossible. It just takes a little extra preparation.
Challenges with Growing Grass on Clay Soil
Nearly all soil contains some amount of clay — the ideal amount of clay for growing most plants is less than 30%. When soil consists of more than 30% clay particles, however, several problems can emerge.
Poor drainage is the most common issue associated with clay-heavy soil. Clay particles are very small and compact, so water has a hard time passing through them. If your soil contains a lot of clay, you may notice puddles forming on the surface after rain or irrigation.
Clay-heavy soil also tends to prevent nutrient and oxygen molecules from reaching plant roots.
Another big problem caused by the compact nature of clay soil is that many plant roots just can’t penetrate the material. As a result, grass growing in excess clay may have stunted, causing shallow root systems.
Testing for Clay in Soil
Soil tests are often utilized to determine nutrient or pH levels. However, many tests also analyze the amount of clay in a soil sample. Soil testing is fairly inexpensive or, in some cases, free. In my experience, these services more than pay for themselves when starting a new lawn from seed.
If you would rather test your soil composition at home, I recommend conducting “The Jar Test” outlined by Clemson University’s Home & Garden Information Center. This little at-home experiment can tell you a lot about your soil’s contents without professional testing equipment.
Testing Clay Density by Hand
Although I’m a big believer in using professional resources like soil testing whenever they are available, it’s also possible to determine the general clay content of your soil by hand. All you need is a trowel and the willingness to get a little bit dirty.
The soil will need to be slightly moist before testing it by hand.
I find the best way to test soil content by hand is by squeezing a golf ball-sized clump of soil in your palm. If the ball is malleable and holds its shape when released — similar to play-dough or modeling clay — it contains a high amount of clay. If it is loose or even crumbles in your hand, it contains more sand than clay.
Another option is to spread a small ball of soil between two fingers. If the consistency is fairly smooth, the soil is made up of small clay particles. If it feels rough, it consists of larger sand particles.
Improving Clay Soil – Fact or Myth
The best way to improve clay-heavy soil is by offsetting the amount of clay by adding other materials to the soil. My favorite soil amendment for this scenario is almost any kind of organic matter.
Other popular recommendations for amending clay-heavy soil include gypsum and tilling but — at least, in my opinion — these improvement strategies aren’t as effective as many people believe and will not provide you with long-term or lasting results.
Incorporate Organic Material
As I said, organic material is by far the best amendment for improving clay soil. It balances out clay’s heavy, compact nature while also adding beneficial nutrients and microbes to the area.
According to Oregon State University, you should spread between 2 and 3 inches of your chosen organic matter over the soil. Use a fork or rototiller to incorporate this material into at least the top 6 inches of soil.
You can use a variety of organic materials for this purpose. Some of the most widely available options include aged compost, lawn clippings, and leaf mulch.
Compost can be made from garden waste, lawn clippings, or kitchen scraps. You can also create compost using live worms (a practice known as vermiculture) or animal manure. Aged compost is ideal for any application — including amending clay-heavy soil — as the decomposition process has already started.
Grass clippings are a nice source of organic material that nearly every property owner has plenty of access to. If possible, I recommend using grass clippings that have started to break down already. Fresh lawn clippings will take longer to fully enrich clay-heavy soil.
Leaf mulch is basically just dry leaves. You can use leaves collected from your garden or source them from somewhere else. Just be sure to select leaves that are free of disease, pests, and chemicals to ensure the health of your future lawn.
Gypsum, or calcium sulfate, is a lawn and garden product often marketed for use in clay-heavy soils. Unfortunately, gypsum’s ability to loosen and aerate clay soil for grass seed is largely a myth.
To be fair, gypsum does work in the proper context. But that context is large agricultural fields, not grass lawns. In my experience, gypsum doesn’t work on the layered topsoils found in residential areas the way it does on heavily worked farmland. You’re much better off adding organic matter to the soil instead.
Rototilling alone is not a miracle cure for dense or compact soil, especially when those qualities are the result of high clay content. However, I do think tilling is an excellent way to incorporate organic matter into the soil. At the very least, it’s easier on the body than mixing compost or mulch into the soil by hand!
Keep in mind that clay-heavy soil is extremely easy to over-till. The most common problem associated with over-tilling clay soil is hard clumping. Also, if you till the top several inches of soil, be wary of creating a layer of packed soil just below the tiller blades’ reach that will prevent water from draining further into the ground.
Preparing Clay Soil for Grass Seed
Prepping the soil is easily the most important step when starting or reseeding a grass lawn. While all types of soil need preparation before seed can be laid down, there are a few steps I think should be paid particular attention to when working with clay-filled soil:
Aerate the Soil
Core aeration is a wonderful practice for overall lawn health. I recommend aerating the soil prior to spreading seed and then as often as annually to maintain the soil’s quality.
If you’re unfamiliar with aeration and what it entails, the concept is fairly simple. Core aeration removes small “plugs” of soil from the ground. The holes left behind allow water, oxygen, and nutrients to better penetrate clay soil that is normally extremely compact.
Top-dress The Soil
Top-dressing is the best way to amend clay soil with organic matter without uprooting the grass in the area. So I recommend top-dressing if you are overseeding a patchy lawn. However, you’ll get better results by fully incorporating the organic matter into the top layer of soil if you’re starting a lawn from scratch.
For top-dressing, apply a layer of organic material that is ½-inch or thinner over the soil. Keeping the layer quite thin ensures the existing grass won’t be smothered.
Testing Soil pH
I find that many people overlook the importance of soil pH when starting a lawn. Most turf grasses thrive in soil that is neutral or slightly acidic — between 6.0 and 7.0 on the pH scale. Clay-heavy soil, however, is almost always alkaline — between 8.0 and 10.0.
You can easily test your soil’s pH using a DIY soil test kit. I suggest taking samples from several areas to be seeded to get an accurate reading. If you’re planning to submit a soil sample for a full analysis, though, there’s a very good chance the results will include a pH reading as well.
Sowing Grass Seed on Clay Soil
As long as the soil is properly prepared, sowing grass seed on clay is not much different from any other soil composition. Adequate moisture is important both before and after planting but this is true of any soil type. However, bear in mind that clay soil will retain water better than sandy soil even on hot days.
Watering the soil several days before planting grass seed is an important step when establishing a new lawn. Ideally, you want to saturate the top 6 to 8 inches of soil at this time. Since water moves much more slowly through heavy clay soil, you’ll need to test the depth of saturation after it has had some time to penetrate the ground.
Watering Schedule for Grass Seed on Clay Soil
One of the benefits of planting grass on clay-heavy soil is the level of natural moisture retention. Once your new grass sprouts roots, it will have a very easy time accessing the water it needs to survive and grow.
With that said, a tailored watering routine is still 100% necessary after sowing grass seed. Your goal should be to keep the very surface of the soil consistently moist. This will create the ideal environment for the seeds to germinate and sprout.
For the best results, I recommend following the basic watering schedule below throughout the first couple of weeks after spreading grass seed:
To protect the seeds and jump-start germination, be sure to water the area immediately after planting. This is crucial even if the soil was pre-watered (though you’ll need to apply less water if that is the case).
Water is long enough that the first couple of inches of soil is well-saturated. This should take between 5 and 10 minutes if the ground was adequately prepared. Be sure to use a gentle sprinkler or hose setting to prevent washing away any grass seed.
During the first week after sowing grass seed, you’ll need to water as often as twice per day. The exact frequency will depend on how much rain your area receives during this time, as well as how hot the days are and how much water your clay soil has retained.
The goal throughout this period is to maintain consistent moisture on the soil’s surface. If your grass seed dries out, it will delay germination or even kill off the seeds.
Because clay is slow to drain compared to other soil components, I recommend light, frequent watering. This will allow the water to seep into the soil without creating puddles or run-off on the surface.
In most cases, you will need to continue watering up to twice a day for several weeks. Once the grass germinates, however, you can scale your watering back to once a day. Most cool-season grasses will germinate within a week or two but some take several weeks.
As you transition to once-a-day watering, you should also start watering more deeply. Saturating the top several inches of soil as your grass seeds sprout will encourage healthy root growth.
Types of Lawn Grass for Clay Soil
When starting a lawn, I can’t stress enough the importance of selecting a grass variety that is suited to your native soil. Choosing clay-tolerant grass will cut down on prep work and maintenance significantly. It will also be better for the environment in the long term since fewer soil amendments (including water) will be necessary.
There are many great turf types of grass out there that will thrive in clay soil. While I encourage you to get local recommendations for your climate, these are some of my favorites in terms of versatility:
Tall fescue is an excellent cool-season grass for any high-traffic area. It excels in clay soil in part because of its deep root system (that can penetrate several feet below the soil’s surface). While it tolerates mild drought quite well, I don’t recommend planting tall fescue if you live somewhere with very dry, hot summers. It’s also not the best choice for shaded lawns.
Buffalograss is a warm-season variety that also has a deep root system relative to other available grasses. Most buffalograss roots extend up to 12 inches deep and can survive harsh temperatures and drought. Personally, I’m a big fan of buffalograss because it requires minimal irrigation once established. But it may need special care during its first year or two.
Pangola grass is a lesser-known variety well-suited to tropical regions. Pangola grass loves moist soil but tolerates drought surprisingly well. While it prefers a balanced soil composition, it is one of the better heat-tolerant varieties for clay soils. This grass is most commonly used in pastures but can make a decent turf grass in the right climate.