Should I Mix Grass Seed With Topsoil?

Mixing grass seed with topsoil before putting it on your lawn can be a good way to save a step for some situations, particularly when spot-applying seed to patches or thinning areas, but it isn’t right for every method of seeding the yard. If you’re using a spreader over a large area, it’s best to just use pure seed for an even application.

This is because grass seeds need light to germinate, and applying seed mixed with topsoil may, if not carefully done, bury the seeds and result in less new grass growth than you were hoping for.

Why Do Seeds Need Light To Grow?

Grass loves sunlight, even cool-season types that are used to shorter days with a fair amount of darkness. Grass seeds need light to germinate since it’s how they make energy. Fresh, dry grass seed contains nutrients and a grass embryo inside of the husk, and once the seed has absorbed enough water to open, sunlight will allow the seedling to perform photosynthesis, grow roots, and eventually sprout blades.

Scotts Turf Builder Rapid Grass Sun & Shade Mix: up to 2,800 sq. ft., Combination Seed & Fertilizer, Grows in Just Weeks, 5.6 lbs

Should I Put Topsoil Down Before Grass Seed?

If you’re applying pure seed to the ground, a layer of topsoil should always be put down first rather than after. Some plant seeds like to be covered to germinate, but grass seeds need to be at surface level to sprout and grow.

Apply Seeds To An Even Ground

Whether you’re applying mixed or pure grass seed to the yard, the ground should be even, and the seeds should be laying on soil, not on top of grass or thatch. This is so roots can grow into the ground, which should be aerated so they won’t have to struggle through compacted soil.

A thinned-out or patchy area may need to be raked before putting down seed and might require some fresh soil for the seed to sit on. To be efficient in your reseeding project, you can apply a seed and soil mixture directly to a freshly leveled patch of ground.

What Is The Best Soil To Mix With Grass Seed?

Michigan Peat 5540 Garden Magic Top Soil, 40-Pound

Grass seeds need a well-aerated and moist environment to sprout. Water saturates the seed, and as the seedling sprouts and grows, it requires a regular supply of water since it has no roots or blades yet to store moisture and nutrients. Most grass seed takes two to three weeks to sprout, then another two to three weeks to grow. During this time, the topsoil should be consistently moist and nutrient-rich to support healthy grass establishment.

The best soil to mix with grass seed should be moisture-retaining and rich in organic material or humus. Soil with too much coarse material, like sand or mulch, will drain quickly and may lead to the seeds drying out. The soil should have space for air, however, so the roots will get enough oxygen and be able to stretch into the ground. Topsoil made with compost and other kinds of humus will give the seeds the support, moisture, and nutrients it needs at the critical stage of initial growth.

Can You Use Garden Soil For Grass Seed?

Miracle-Gro Raised Bed Soil, 1.5 cu. ft.

Garden soil is a great choice to mix with grass seed. It is rich in nutrients from compost and special formulas that provide a balanced amount of vitamins and minerals directly to the growing plant. Potting and garden soils are made with materials that hold moisture, creating a supportive environment for grass growth.

Make Sure There Are Enough Seeds In The Soil Mixture

The main challenge of mixing seeds into soil is making sure there are just enough seeds and soil for them to not get lost or buried. The soil mixture should look as full of seeds as you would expect the ground to look from an application. The mixture should be applied at a thickness of about 1/4 to 1/2 inch. This way, the seeds will be embedded in the soil but exposed to the air and light. Be sure to pat the soil down, but don’t compact it too much.

Benefits To Mixing Seed Into Soil

When you mix seed into soil for patch applications, other than saving time, there are a few benefits to your lawn:

  • Avoids applying too much seed at once – By mixing seed into the topsoil before putting it down, you’re in control of how much seed gets put in. When spot-seeding patches or thinning areas with pure seed, they might get applied unevenly or too generously. An even mix will ensure a consistent application.
  • Easy to move around – Mixing seed and soil in a wheelbarrow or a bucket helps you carry around the mixture from spot to spot, rather than carrying soil, seed, and fertilizer in shifts. This can be a big time saver!
  • You can add what you like – When you mix the topsoil and seeds yourself, you choose the soil and any additives that might help your yard. Doctoring your soil with a little compost, clay (for drier soils), peat moss (for drier soils), or sand (for wetter soils) can help your seeds grow in the most supportive conditions.
  • Adds soil content to the yard – When you apply topsoil or compost with grass seed, you’re adding bulk to your yard. Rain, wind, and plant growth will deplete the soil, so regularly adding new topsoil or topdressing will keep your turf in place and growing strong.
Benefits To Mixing Seed Into Soil

Should I Mix Seed With Soil To Overseed?

Mixing seed into soil when overseeding won’t hurt, but it isn’t necessary. The additional soil will add bulk to your turf, but it will disburse with the seeds, and too much extra soil can cover the existing grass blades. Similarly, the soil may add extra cover to the seeds, which will be receiving some shade already from the grass.

Any added fertilizer to the mixture may encourage the existing grass to grow, which may cast more shade on the seeds and prevent proper germination.