Does moss kill grass?

No. Moss is opportunistic and colonizes bare ground where grass already failed. Finding moss tells you the growing conditions stopped suiting grass, not that the moss attacked it.

Does moss mean my soil is acidic?

Not necessarily. Low pH is one possible cause, but shade, compaction and poor drainage are more common. A soil test costs very little and stops you liming a lawn that did not need it.

What kills moss in a lawn?

Iron sulfate products blacken moss within days. That is cosmetic though. Unless you change the conditions that favored it, the moss returns within a season.

Can grass grow back where moss was?

Yes, once you rake the moss out and fix whatever caused it. Bare patches need overseeding, ideally with a shade-tolerant fine fescue if shade was the underlying problem.

Moss Instead of Grass: What Your Soil Is Telling You

Moss is a symptom, not a cause. It does not out-compete healthy grass or poison it. It moves into ground the grass has already vacated. So the useful question is never how to kill the moss. It is why grass stopped growing there.

The five conditions that favor moss

Usually more than one is in play.

Shade. The most common by a distance. Grass needs roughly four hours of direct sun minimum, and most lawn mixes want considerably more. Moss is perfectly happy with less.
Compaction. Hard soil restricts roots and holds water at the surface. Moss has no real root system, so it does not care.
Poor drainage. Low spots, heavy clay, or a lawn that stays wet for days after rain.
Low fertility or low pH. Grass is fussy about both. Moss is not.
Mowing too short. Short grass thins, lets light reach the soil, and hands moss the opening.

Diagnose before treating

Test the pH. A soil test is the cheapest useful thing you can do here. Grass prefers roughly 6.0 to 7.0. If your pH is fine, skip the lime, because liming a lawn that did not need it makes other nutrients less available and creates a new problem.

Check the light. Watch the area over a full day. Under four hours of direct sun, no grass seed fixes this permanently, and you are choosing between pruning for light or accepting a shade planting instead of turf.

Push a screwdriver in. If it stops short in moist soil, you have compaction, and that is solvable: when to aerate.

Look at where water sits after heavy rain. Standing water for hours means drainage is the real project.

The order that actually works

Fix the conditions. Prune branches for light, aerate compacted ground, improve drainage, correct pH if the test says so, feed if the lawn is genuinely underfed.
Kill and rake out the moss. Iron sulfate, then physically remove the dead material. It comes up easily because it has no roots.
Overseed the bare ground immediately. Moss leaves bare soil behind, and bare soil grows whatever arrives first. Timing in when to overseed a fescue lawn, watering in how often to water new grass seed.
Mow higher from now on. Three and a half to four inches shades the soil, and it is the simplest long-term moss suppression available.

Choosing seed for shade

If shade is the cause and you cannot remove it, the seed matters. Fine fescues, meaning creeping red, chewings and hard fescue, tolerate shade far better than Kentucky bluegrass or ryegrass. They are also lower-maintenance, which suits areas under trees where you are already competing with roots for water.

What to do next

If moss keeps returning to the same spot, the underlying condition was never addressed. A recurring problem in a fixed location is worth digging into properly rather than reseeding annually: why the same patch thins out every year.

And if the lawn feels soft underfoot as well as mossy, you may be dealing with two problems at once: why is my lawn spongy.