Hello jankopera,

Kill the crabgrass first, then aerate, then seed. And no, slit‑seeding is not necessary if you aerate properly—but it can improve results in badly thinned areas.

Here are some resources at the links below:

Establishing a New Lawn Using Seed - MSU Extension

Late season lawn seeding - Gardening in Michigan

Tips for seeding lawns in September - Turf

Below is the Michigan‑specific, research‑based breakdown you’ll appreciate.

What to do first in a lawn that is now ~50% crabgrass

Crabgrass is an annual that dies in fall, but in Michigan it leaves behind a dense mat of seedheads that will re‑germinate aggressively next summer unless controlled.

Because your lawn is heavily infested, renovation without killing crabgrass first will fail. Aerating and slit‑seeding into live crabgrass simply gives the crabgrass more space and light.

Step 1 — Kill the crabgrass

For Michigan, the most effective and safest approach is:

Use quinclorac (Drive XLR8 or a quinclorac‑containing combo).

It is the only selective post‑emergent that reliably kills mature crabgrass.

Safe on Kentucky bluegrass, perennial rye, and tall fescue.

Works even on large, tillered crabgrass.

Avoid glyphosate unless you are doing a full‑kill renovation. You’ve been
cautious with herbicides near trees and wells, and quinclorac is the correct
selective option here.

Timing

Apply quinclorac now, while crabgrass is actively growing.

Expect browning in 7–14 days.

More information at this link:

Pain in the grass: Crabgrass - Turf

Step 2 — Aerate

Once the crabgrass is dying or dead:

Core aeration opens the soil, improves seed‑to‑soil contact, and helps recovery from snow mold thinning.

Aeration alone is enough for overseeding if the soil surface is not crusted or compacted.

Given your snow mold + thatching + bare dirt patches, aeration is absolutely appropriate.

Step 3 — Seed

After aeration:

Broadcast seed over the aerated lawn.

Rake lightly or drag a section of chain‑link fence to improve contact.

Apply starter fertilizer (you prefer organic—Espoma Organic Lawn Starter is a good Michigan‑appropriate option).

Is slit‑seeding necessary?

Not required, but here’s the nuance:

When slit‑seeding adds value

Large bare areas (bigger than 1–2 ft²)

Soil surface is smooth and hard

You want maximum establishment in one season

You’re renovating >30–40% of the lawn

When aeration alone is enough

You have many small bare patches but not large dead
zones

Soil is already loosened from thatching

You’re overseeding Kentucky bluegrass or perennial rye
(both germinate well with aeration)

Given your lawn is 50% crabgrass, you likely have large open areas once the crabgrass dies. In that case, slit‑seeding will give you a denser, more uniform stand and reduce weed invasion during establishment.

If budget or time is tight, aeration + overseeding will still work—but slit‑seeding is the higher‑success option for a lawn this thin.

Michigan timing (critical)

August 15 – September 15 is the ideal Michigan seeding
window.

Soil is warm, nights are cool, and weed pressure drops.

Crabgrass will die soon anyway, but killing it now prevents seed production and gives your new turf a head start.

Your best sequence (Michigan‑optimized)

Apply quinclorac to kill crabgrass.

Wait 7–10 days.

Core aerate.

Slit‑seed the worst areas; overseed the rest.

Apply organic starter fertilizer.

Water lightly and frequently until established.

Apply pre‑emergent (prodiamine or dithiopyr) next spring to prevent crabgrass from returning.