Perhaps you have a window sill needing some simple greenery, or your lawn has some bald spots you need to tend. In either case, you may wonder if you can sow grass seed in potting soil. Well, you are in for some good news today!
You can use potting soil with grass seed. Potting soil retains moisture more effectively than most native soils and provides fertilizer to help with seed germination. Combine potting soil with topsoil, and use a seed spreader or place seeds by hand to fill patches in your lawn for best results.
This post explains what you need to know about combining potting soil with grass seed, whether you want to grow grass in containers or outdoors. Keep reading for tips and tricks you should know before getting started!
Growing Grass Seed in Potting Soil
Potting soil is excellent to use on its own for germinating and growing grass seeds, especially in containerized production. However, to grow a whole yard full of turfgrass, potting soil needs some assistance to sustain a healthy lawn throughout the seasons.
Despite the name, most potting soils don’t contain any actual soil. Since people typically use these products for containerized plants, the soil isn’t an ingredient because it’s considered too heavy for most houseplants.
Instead, potting soil typically is made from one or more of the following ingredients (and no, this is not a comprehensive list):
- Coco coir (aka coconut coir or coco moss)
- Peat moss
- Sphagnum moss
It’s also helpful to know that potting soil is technically not the same as a potting mix. However, you’d never know that based on commercial advertising or everyday conversation, as people mistakenly interchange these terms all the time.
The difference is that potting mix is potting soil plus soil enhancers. However, many said enhancers are simply other ingredients that comprise potting soil (peat moss, vermiculite, perlite), so the difference is somewhat obscure. Just know that you might see a significant range in the nutrient levels between these two labels.
Each ingredient in potting soil offers different benefits, and specific plants require certain elements to support optimal growth. Many brands will add slow-release fertilizers and conditioners for additional nutrients, and some premium options may also include natural topsoils.
Nutritional Requirements of Grass
Depending on the grass seed you’re growing, you may need to focus on obtaining higher levels of certain nutrients in your potting soil. Still, in general, the top three macronutrients most important to proper grass seed germination, growth, and overall health are N-P-K:
- Nitrogen (N) – An essential nutrient for all plants, nitrogen is necessary for photosynthesis and creating chlorophyll. Each grass type requires a certain nitrogen level for optimal color and healthy growth. Consumed in the form of nitrate, nitrogen leeches easily from soils and frequently needs replenishing.
- Phosphorus (P) – Phosphorus is essential in many of the most complex plant functions. It supports energy transfer, regulates protein synthesis, and is a vital component in producing new plant tissue and cell division. Correct phosphorus levels are essential for proper root growth and development.
- Potassium (K) – The primary job of potassium is to create a more robust, hardier plant. It helps with early growth and improves a plant’s efficiency in water use. Potassium also makes the grass more resistant to environmental stressors such as pests, drought, and extreme temperatures.
Some other essential nutrients grasses need in the soil to grow are:
Should I Mix Grass Seed Into Potting Soil?
You should not mix grass seed into potting soil when seeding a whole yard. Mixing seeds in the soil and then spreading the mixture to seed can help to save time when filling thin spots or bald patches, but this method produces mediocre results when seeding a new lawn.
Grass seeds need plenty of light to sprout, and mixing them into your potting soil and topsoil mixture covers some of the seeds, preventing them from receiving the sunshine. Typically, this results in thin and spotty new grass growth.
Instead, you should first spread a layer of potting soil over the area and use a seed spreader to ensure an even application and achieve the best results.
You should ensure that your potting soil has been properly stored to avoid any potential harm to your plants. If you would like to learn more about potting soil issues such as mold, check out my article: Is It Normal for New Potting Soil to Smell Moldy?
How To Use Potting Soil With Grass Seed in Lawns and Large Gardens
Potting soil should be a supportive player to your native topsoil when growing a lawn from grass seed. So, the first step is to test your soil to determine its nutrient contents and pH level so you can find the most complimentary potting soil.
With that accomplished, using the potting soil to grow grass seed is easily done in these five steps:
- Use a garden tiller to loosen the topsoil. Break up the top 3-4 inches (7-10 cm) of soil to clear debris and aerate the land.
- Mix potting soil with topsoil. Apply enough potting soil to create an even mixture with your topsoil. Doing this helps ensure the nutrients available in each are available for every seed.
- Use a seed spreader to lay the grass seed. For smaller areas, you can spread the seed by hand. Be sure to cover the area as completely as possible, then go back and lightly rake the soil to encourage the seeds to settle into the soil.
- Flatten the area with a lawn roller. This step serves a dual purpose, as it helps to create a level surface and pushes the seeds into the soil to ensure they properly establish roots.
For more tips and tricks for how to use potting soil to seed a lawn, check out this short YouTube video from Garden & Lawn:
How To Use Potting Soil With Grass Seed in Containers
Window boxes and small pots of grass are easy ways to liven up your home. The seeds of most annual grass varieties germinate within a week and grow green for 60 days or more in containers of potting soil with regular watering and sunshine.
Once you’ve selected your desired grass seed and potting soil, select a pot or container with drainage holes. You’ll also need a drip tray—at least, to get started. Then, follow these simple steps:
- Prep the potting soil for seeding. Fill your container with potting soil, and water it thoroughly until it drains and fills the drip tray. Leave the soil to hydrate for around half an hour, then pour off any water remaining.
- Apply a single layer of seeds over the surface, covering as much of the soil as possible. Use your finger to press the seeds to create a good bond with the soil. Sprinkle a light layer of soil over your seeds if the variety of grass calls for it.
- Moisten the soil and leave seeds to sprout. Use a spray bottle to moisten the soil surface. It shouldn’t need too much since you’ve hydrated it already. Put a plastic bag or film over the container to help retain the moisture, and place it in a warm, sunny spot.
- Maintain and enjoy! Once your seeds start to sprout, you can take off the plastic. Keep the soil moist as the grass grows by watering one to two times weekly.
Many advantages come with using potting soil for growing grass. Potting soil drains well and is excellent at retaining moisture. It also assists with aeration in plant roots and contains fertilizer to support optimal growth. Plus, since potting soil is sterile, you can use it on your lawn without fear of consequences to your native soil.
If you’re planning to grow a lawn of grass in your yard, test your native soil to determine its nutrient content before selecting a potting soil.