Lawns usually take up a large portion of our land; and for good reason. If you look at new construction homes with and without lawns, you will find that houses that have a lawn have much higher construction costs compared to those without.
However, at the same time, you will also find that the selling price of houses with a lawn is much higher than of those without. The aesthetic appeal added by a lawn with fresh grass is much more and comes at a fraction of the cost. However, if your lawn is too big and you want to build something on it, you might be wondering how to get rid of the grass in a given space. What would happen if you put dirt over grass?
Adding dirt over grass to build on it is never a good idea. However, if you are looking to simply level the place or repair a lawn, you can get away with dumping new soil on top and preparing it for sod/seed. There are a few intricacies to keep in mind when doing so; which we will discuss in detail here.
What Happens If You Put Dirt Over Grass?
The reason the concept of putting dirt over grass seems so attractive is that it seems like a rather cost-effective rebuilding solution. But we’re here to tell you this isn’t always the case. It may not seem like it but grass is considered to be a stubborn plant.
Think about it; what other plant (other than weed) is there that you can cut so relentlessly and which will grow back more resilient than before? Grass strains such as Kentucky Bluegrass, Buffalo grass, and other similar strains can wriggle their way out of up to 5-inch-thick dirt layers if watered enough.
Whether or not it is a good idea to put dirt over grass depends entirely on how thick of a soil layer you are putting over the grass. Typically, a 5-inch layer is enough to kill off most grass types, but more resilient plants and almost every other weed type can make its way through the layer after a while – especially if it keeps getting watered or isn’t exposed to the sun so as to dry it out.
You can choose to use herbicides to kill off the weeds, but since you’ll be covering it all up and the herbicide won’t get washed away, chances are that you are going to have long-term impacts of the same years later. You’re in for a bigger problem if during that time a weed seedling decides to develop resistance to your herbicide because of overexposure.
In most cases, people may want to build a patio on top of the dirt layer. For a patio, you will have to pour at least 12 inches of dirt on top and compress it properly – enough to bring it down to 8 inches. An 8-inch layer is enough to prevent plant growth even if the topsoil isn’t compressed; provided it isn’t being watered.
Having said that, the 12-inch layer compressed down to 8 inches won’t have enough room within the grains to allow for plants to grow; even if watered.
If you are planning to add dirt over grass just to repair your lawn, we would recommend laying only an inch or 2 at most. If you are planning to build a raised bed on top of grass, we recommend keeping it at least 6 inches higher and planting your seeds as quickly as you can.
It should take your average grass species at least three weeks to grow through an inch of dirt. Less if the dirt has a lot of compost in it and is being watered frequently.
A Practical Example
We added 2 inches of dirt with very little amount of compost in it during the monsoon season.
This isn’t recommended, but we wanted to test out what would happen. The grass grew within the month (23 days) to create a lush green layer on top, but it was extremely uneven. Since the grass had already grown and was thriving, we didn’t have many options with regards to leveling it out. So instead, we ended up adding more dirt to level everything off.
In the next monsoon season, we added 12 inches of dirt and left it as is (without compressing). Within 2 weeks we found that weeds had started to grow. We pulled one out to test whether it was from the soil underneath or the dirt we added. It was from the soil underneath.
About a month and a half later, we dug through the dirt and found that the grass had eventually died. This means that a foot or more of soil over grass is enough to kill the grass and eventually turn it into a part of the soil. Bacteria will eventually start decomposing the grass, turning it into a very good source of compost for your new plants – or weed.
Having said that, we would recommend that you sod strip your grass before adding soil on it. You can actually sell the grass to someone who needs it to cover some (or even all) of the costs associated with adding dirt.
Remember, when you add dirt on top of any plant, be it grass, weed, or even a flower as delicate as the rose, you will deprive it of fresh air and sunlight. This puts the plant in overdrive. Some plants have enough reserve food to grow through small layers, such as grass.
Otherwise, you will suffocate the plant and it will die. Bacteria will then start digesting and turn it into compost. This should give you soil rich in nutrients. You can plant your plants on top and see them thrive pretty well.
Regrading the Soil
If you are simply looking to repair your lawn, we recommend regrading it. You have two options here; either start by stripping sod and digging at the highest point in your lawn to level it out or to add dirt in the compressed area.
To ensure your grass actually does grow back, make sure the depression isn’t more than 2 inches. We recommend only adding a 2-inch layer at a time if you want your grass to survive. Another very important consideration to make is that when looking to build up new soil, your drainage is going to be affected in negative ways.
We recommend you get a good idea of your drainage from the highest to the lowest point in your lawn and make arrangements accordingly.
If you are looking to get rid of an invasive grass species, we recommend placing a layer of cardboard before filling the dirt.
Once you have identified the depression levels and how much dirt needs to be added, start pouring on top and measure it every now and then with the help of a straight edge and a spirit level. Add dirt, level it, check whether more needs to be added and do the needful. It is easier to add dirt than to remove it, especially if there is grass underneath, so be careful.
Finding the Right Dirt Type
It is important that the dirt or topsoil you are adding matches the texture and type of what you already have in place; otherwise you risk not only shocking your plant but also introducing patches into your lawn. One dirt type might be more fertile than the other while the other might be coarser and limit grass growth.
Dirt and topsoil often contain rocks and debris; not to mention insect larvae and weed seeds. Since dirt or topsoil isn’t regulated, you have to check the dirt you are adding on your own accord. We recommend using 4/10 cubic yard of topsoil per 1,000 sq. feet to repair your yard.
To regrade your lawn effectively, you will need:
- A Shovel
- Straight Edge
- A Brush
- A Very Strong Back
Once you have everything:
- Start by mixing the soil with compost. Don’t skip this, since it can help you get a better feel of the soil you are about to add; not to mention how it airs the soil and slows down weed/bacteria colony growth.
- Fill a wheelbarrow with the aired soil and take it to where you need to add it.
- Place a straight edge to determine how much you need to add.
- Add a few shovels (as needed) and measure again. Work your way from the corners and move inwards.
- If you are looking to add soil on your whole lawn to refresh it, we recommend applying no more than ½ inch of the mix. The grass will be able to grow through up to 2 inches, but it will strain the root system significantly. ½ an inch is enough to revitalize the grass.
- Rake the new soil.
- Brush the grass with a to and fro motion to remove as much debris as possible from grass blades.
- Water the area lightly. Do not overwater; or else you will wash away the soil you just added, which will settle at the nearest depression again, leaving you with patches to refill.
- Keep a close eye on the grass and monitor its growth.