Top Soil or Compost for Overseeding – Which is Better?

Overseeding is a crucial lawn care practice that thickens up thin and patchy lawns by introducing new grass seeds into existing turf grass. A thick, lush lawn not only looks fantastic but also helps choke out weeds and withstands heavy foot traffic better.

When overseeding, using the right soil amendment together with grass seeds can make all the difference between success and failure. The age-old question faced by homeowners is whether to use top soil or compost as the topdressing when overseeding lawns.

In this comprehensive guide, we will dig deep to unravel this dilemma once and for all. We will compare top soil and compost to determine which one is the better choice for overseeding your lawn and achieve a thick, verdant turf

Why Topdress with Soil Amendments for Overseeding?

You may be wondering why you can’t just spread grass seeds directly on your lawn without adding any soil amendments like top soil or compost. Well, there are some compelling reasons why topdressing with the right amendment is crucial when overseeding:

• It helps keep grass seeds in place and prevents them from being washed or blown away.

• It improves seed-to-soil contact leading to higher germination rates and better establishment.

• It provides essential nutrients for grass seedlings to get off to a vigorous start

• It retains moisture close to the surface for tender grass shoots.

• It creates a barrier between seeds and birds looking for an easy meal.

Top Soil for Overseeding Lawns

Top soil is the uppermost layer of soil, usually the top 3 to 8 inches, that contains most organic matters and nutrients. When used for overseeding, here are the main pros and cons of using top soil as the topdressing:

Pros

• Levels bumps and divots to create a flat surface for even growth.

• Provides good stability and anchorage for grass roots.

• Its mineral content balances pH for healthy growth.

• Offers quick establishment due to nutrient availability.

Cons

• Leads to uneven settling over time.

• Too thick of a layer can smother existing grass.

• Introduces risk of weeds, pests, and diseases.

• Offers no long-term improvement in soil structure or fertility.

• Dries out faster and needs frequent watering.

• Can contain clods which hinder seed-to-soil contact.

Compost as Topdressing for Overseeding

Compost is decomposed organic matter that results from the breakdown of materials like food scraps, leaves, manure, and grass clippings. Here are some benefits and drawbacks of using compost when overseeding:

Pros

• Releases nutrients slowly to feed grass seeds and roots.

• Improves moisture retention and reduces watering needs.

• Inoculates beneficial microbes that enhance soil health.

• Helps loosen clay soils and increases aeration.

• Environmentally-friendly and sustainable choice.

Cons

• Provides no help with leveling an uneven lawn.

• Potency varies based on compost feedstocks and process.

• Immature compost can damage tender grass shoots.

• Some kinds may contain viable weed seeds.

• Requires reapplication to maintain effects year after year.

Which is Better – Top Soil or Compost for Overseeding?

So when it comes to choosing between top soil versus compost for overseeding existing grass, which one should you pick? Here are some key pointers to help you decide:

• For extremely bumpy and uneven lawns, top soil is the better choice to level the surface for uniform growth.

• Mature, high-quality compost is preferable for improving thin or worn-out lawns by enhancing soil fertility and structure.

• A balanced approach would be to use a thin layer of top soil just to smooth out major bumps and hollows. Then apply 1/4 to 1/2 inch of compost over the seeds to provide nutrients.

• For predominantly clay soils, compost helps aerate the ground and makes it easier for tender grass roots to establish themselves.

• Sandy soils that drain too quickly are better served by compost’s ability to retain moisture compared to fast-drying top soil.

• If using top soil, inspect it thoroughly because poor quality types may contain viable weed seeds, undigested wood chips, and stones.

• Well-decomposed, weed-free compost provides organic matter to soil while minimizing the risks associated with bringing in outside top soil.

5 Simple Steps for Overseeding with Compost Topdressing

For best results, follow these simple steps when using compost as the topdressing for overseeding your lawn:

Step 1: Mow the lawn shorter than usual to a height of 1 to 1.5 inches. This removes any material that can hinder seed-to-soil contact.

Step 2: Use a core aerator to punch holes across the lawn so compost and seeds can penetrate the soil surface.

Step 3: Spread a 1/4 to 1/2 inch layer of weed-free, finely screened compost using a broadcast spreader.

Step 4: Broadcast grass seeds according to the recommended rate for your lawn’s square footage.

Step 5: Use a stiff rake to lightly work compost and seeds into the aeration holes. Then water gently to moisten the topdressing.

Optional Step: Consider rolling the lawn with a water-filled lawn roller to press seeds firmly against compost and soil.

When to Avoid Using Straight Compost for Overseeding

Despite its benefits, there are a few scenarios where compost alone may not be the best choice for overseeding lawns:

• If major depressions or humps exceed 1 inch, compost cannot level the surface adequately.

• Pure compost topdressing on a thick lawn mat or heavy thatch can create floatation, preventing seed-soil contact.

• Low-quality compost containing large pieces of twigs or uncomposted materials can cover seeds instead of nurturing them.

• On sandy soils in arid regions, compost alone may not provide sufficient anchorage for seeds, increasing washout risk.

• Where weed pressure is high, seeds in pure compost are more prone to bird attacks without soil covering them.

Maintaining Your Overseeded Lawn

Once you have completed overseeding, proper aftercare is vital for the grass seeds to flourish. Here are some tips:

• Water lightly and frequently, keeping the top 1/2 inch moist until seeds germinate.

• Allow soil to dry out partially between watering once seedlings are established.

• Apply a starter fertilizer high in phosphorus to fuel root development.

• Mow existing grass high (3-4 inches) to allow sunlight to reach establishing seeds.

• After new grass reaches 3 inches, begin mowing regularly at the desired height.

• Let new grass thicken up before resuming heavy use and foot traffic.

The Bottom Line

When overseeding thin, patchy lawns, using compost offers substantial benefits over top soil as the topdressing in most cases. Compost boosts soil health and fertility while avoiding the potential downsides of bringing in outside top soil.

However, for extremely bumpy lawns, a thin layer of top soil may still be required before applying compost and grass seeds. As always, the condition of your existing lawn and soil will dictate the best approach. Follow the tips above to give your grass seeds the best chance of success when overseeding with compost.