# When to mow new grass for the first time

> When to give newly seeded grass its first cut: the one-third rule, the walk test for firm roots, mower height and weight, and what to do after the first mowing.

Canonical: https://lucernel.com/guides/when-to-mow-new-grass
Last updated: 2026-10-21

Type: Guide. Publisher: Lucernel.

## Short answer

Mow new grass for the first time when it is about one-third taller than the height you want to keep, for example just before it reaches 4 inches if you mow at 3 inches, and only once the seedlings are rooted well enough to stand back up after you walk on them. Use a light, sharp mower and never take more than a third of the blade.

- **Choose this if:** Measuring with a ruler once a week is enough for a small seeded patch.
- **Choose the other option if:** Lawnzo helps when you want the first cut, watering and the next feeding planned from the day you seeded.

## Side by side

| | Ruler and memory | Lawnzo |
| --- | --- | --- |
| Mowing height for your grass type | Partly, you look it up | Yes, grass-specific |
| One-third rule applied as you log | No | Yes |
| Weather check before mowing | No | Yes, keep, delay or skip with the reason |
| Seeding, watering and feeding in one plan | No | Yes |
| Journal with photos | No | Yes |

## The one-third rule

Penn State Extension advises mowing newly established turf when the grass is no more than one-third higher than the cutting height you want. If you plan to mow at 3 inches, begin just before the grass reaches 4 inches. Taking off more than a third at once stresses young plants.


## The walk test

Height is not the only signal. New grass has to hold the weight of the mower and of the person pushing it. Penn State suggests walking onto the new turf and looking at your footprints: if the grass plants move back upright, you can probably begin mowing. If they stay flat, wait, or you risk trampling seedlings into the soil.


## How to make the first cut

- Use a light mower with a sharp blade, so it cuts cleanly instead of tearing or pulling seedlings.
- Mow when the grass and soil are dry.
- Turn slowly and avoid sharp turns on the new area.
- Keep watering lightly after the cut until the lawn is established.

## After the first mowing

New lawns often need more food than the starter fertilizer gave them. Penn State notes that an application of ½ lb of nitrogen per 1,000 sq ft, four to eight weeks after the starter fertilizer, helps thicken new turf. Our free lawn fertilizer calculator turns that rate into pounds of your product.



Disclosure: Lawnzo is made by Lucernel, the publisher of this article.

## Frequently asked questions

### How long after seeding can I mow?

Until the grass is one-third taller than your cutting height and the seedlings spring back when walked on, which usually takes a few weeks depending on the grass and the weather.

### How short should I cut new grass?

Never more than a third of the blade at once. If you keep your lawn at 3 inches, cut just before the grass reaches 4 inches.

### Should I fertilize after the first mow?

Penn State suggests ½ lb of nitrogen per 1,000 sq ft four to eight weeks after the starter fertilizer.

### Can I mow wet new grass?

It is better not to: wet soil and seedlings tear and rut more easily under a mower.

### Is Lawnzo available?

See the official app page for current availability and pricing.

## Our pick: Lawnzo, what to do for your lawn, and when

From the day you seed, Lawnzo plans watering, the first cut at the right height for your grass and the next feeding, and checks each job against the forecast.

- Grass-specific height and the one-third rule
- Weather checks that keep, delay or skip a task
- A journal of every job with photos

[See how Lawnzo works](https://lucernel.com/apps/lawnzo)

## Sources (checked 2026-09-26)

- [Penn State Extension: Lawn establishment](https://extension.psu.edu/lawn-establishment)