When it comes time to plant some grass seed in your outdoor space, you might realize the native soil isn’t the best material for a thriving, green lawn. Before you add any inputs to your soil, it’s a good idea to learn about compost vs. topsoil for new lawn, since these are two of the most popular lawn additions.
Both of these materials can help you establish new grass. However, they are two very different substances with their own place and use. We’re going to help you become a bit more familiar with compost and topsoil so you can figure out which one is best for your lawn.
What is Compost?
Compost is decomposed organic matter made from waste such as mushroom substrate, food scraps, leaves, cotton burr, and more. After microbes break these wastes down, a nutrient and biologically rich substance called compost remains.
Within this broad definition, there are a lot of different types of compost that can vary quite a bit. While one substance might be high in nutrients, another might only provide a small amount of nitrogen. So, it’s a good idea to test compost before applying it to your lawn.
Another important note is that compost is much different than soil! While most soil only includes a small amount of organic matter, 3-6%, compost is 100% organic matter.
What is Topsoil?
Topsoil is the top few inches of soil, hence the name. While many people equate this word with rich, dark soil, this isn’t necessarily the case.
Soils greatly vary across regions. While the top few inches of soil in one area might be a nutrient-rich silt loam, topsoil may be straight sand or heavy clay in another place.
The truth is there isn’t a legal definition for topsoil, so you never know what you’re going to get when you buy a bag or load of this material.
Items to Look for When Purchasing Topsoil
Since not all topsoil is the same, there are a few items you should take note of before you purchase some of this material for your lawn.
Soil contains three different sizes of inorganic material – sand, silt, and clay – as well as organic matter. The fractions of these materials determine many important soil characteristics, including water-holding capacity, drainage, nutrient-holding capacity, and aeration.
While you can determine a rough estimate of a soil’s composition by feel, it’s best to conduct a soil test to get an accurate measurement. Many reputable topsoil dealers will have test results on hand. If they don’t, you can always ask for a sample to submit to a soil lab.
One potential downfall of applying topsoil is introducing weed seeds. The presence of weed seeds relates to two main factors: the origin site of the topsoil and the environment where the soil is stored.
Since there aren’t many regulations regarding topsoil, it’s hard to tell the origin of the specific product you’re considering purchasing. It could be from prime cropland designated as a development site, or it could be from a roadside or forest. If there were a lot of weeds present in the area the soil is from, there are likely copious amounts of weed seeds in the soil.
While you may not be able to determine the soil’s origin, it’s easier to see how it’s stored. If you visit a location that has lots of overgrown weeds around its topsoil mounds, it’s best to look someplace else since these weeds will introduce weed seeds into the soil.
Some topsoil retailers add other materials to the original soil to improve the pH, structure, and nutrient content. Commonly added amendments include wood ash and compost. Most retailers are upfront about any amendments, so just ask.
Residual Pesticides and Herbicides
Another hazard to watch out for in topsoil is chemicals leftover from previous applications. If the soil was removed from an agricultural area, you should inquire about any chemicals used on the land.
When Should I Use Topsoil for a New Lawn?
If you’re looking at your future lawn and doubting that there’s enough soil to enable grass seed germination, you could benefit from some additional topsoil.
Here are a few instances when it makes sense to apply topsoil before establishing a new lawn using seed:
- The original topsoil has been eroded or removed, so there isn’t any soil where the seed can germinate.
- The area is uneven or filled with holes, so you need additional material to create a level surface.
When Should I Use Compost for a New Lawn?
If your native soil could use a boost, it’s a good idea to apply some compost before you add grass seed.
Compost applications can especially benefit soils that are high in clay or sand. In clay soils, compost will help alleviate compaction, increase drainage, and improve aeration. In sandy soils, adding compost will help soils hold water and nutrients.
No matter what type of soil you’re starting with, compost can help boost levels of beneficial microbes. When you improve soil life, you also improve the quality of plants. Even though you might think grass is hardy enough to survive anything, it grows best in a nutrient-rich environment.
While compost will improve soil, it’s not the best material to directly plant into. If you’re trying to add multiple inches of material or fill some large holes, you’re better off using topsoil.
If your new lawn needs a boost to get started, topsoil and compost may be able to help. Before you decide on one of these materials, remember that they’re two very different substances!
Compost is great for improving the structure and composition of native soils, allowing for better seed germination and plant growth, while tpsoil can help fill in gaps due to a lack of native soil.
And remember, you can always add both compost and topsoil before establishing a new lawn!