After seeding your lawn — whether reseeding it entirely or overseeding existing turf — timing when to mow it for the first time is critical. Newly seeded grass is still in a delicate growth stage, and you don’t want your hard work and effort to go to waste by mowing at the wrong time.
Timing that first mowing shouldn’t be based on a number of days, weeks, or even months. Instead, it’s best to watch and wait until the grass is three to four inches tall and then mow…unless of course you are growing a low growing grass type then things change a bit.
Grass grows at different rates depending on the type of grass you planted and the climate conditions when you plant. Some lawns may reach 3-4 inches in height and be ready to be mowed in two to three weeks. Others may take up to two months. Hence, why it’s not in your lawn’s best interest to follow a strict timeline after starting new seed.
But why is it important to let your new grass get this tall before mowing?
Waiting until the grass is three to four inches tall gives the roots time to establish themselves in the ground. If you mow too early, you can pull the blades of grass out of the soil entirely instead of cutting the tops off since the root system isn’t fully developed yet. Mowing too early also compacts the soil, impacting early root establishment. This compaction from the lawnmower keeps the roots from growing outward and down through the soil profile.
FYI – I use a product around this time called CytoGro on my baby grass to stimulate faster and deeper root development. You can read more about how it works here.
There are however ways that we can start cutting the grass sooner; although this will mostly apply only to those people looking to maintain shorter cut grass and those who are willing to buy special equipment which we will touch on later in this article.
No matter what though, it’s also crucial to not let the grass get too long before cutting it for the first time. Removing too much height at one time depletes the grass’ stored energy reserves, significantly weakening the turf.
For overseeding this is of particular concern because the established grass can easily outpace the baby grass in growth speed. There are ways to deal with this though which I will cover further into this article.
When your new grass is three to four inches tall, it’s time to mow, but do so carefully to avoid damaging the young sprouts.
Related Reading: How Long Does Grass Seed Take To Fully Grow?
Using a Reel Mower Instead Of A Rotary Mower Changes Things
If you are using a standard rotary mower you should allow the lawn to dry for a day or two beforehand. Dry grass blades don’t get tangled together when you’re mowing, and they are cut by the mower instead of torn. Also, make sure the mower’s blades are incredibly sharp, remove no more than one-third of the height, and turn carefully to avoid pinching the turf and pulling it from the soil.
Unless you are using special equipment like a reel mower or you are dealing with an overseeded lawn, waiting until the grass has reached this recommended height and mowing carefully, you allow the root system to establish and minimize the amount of stress the grass experiences. Thus, keeping it healthy and thriving.
I even made a full video discussing this concept which I’ve embedded below. Alternatively you can see the following post for more on timing your grass seed application in the fall.
I’ve got a lot of extra information on seeding and overseeding here if you want to dive down that rabbit hole.
Some Basics Facts To Keep In Mind
Now, there are some basics that you need to keep in mind before you jump into mowing new grass. The ideal time to mow your new grass depends on several things that I’d like to go into in greater detail below.
Type of Grass: The type of grass is one of the main things you might want to keep in mind. This is so because the right time to mow a grass varies from one grass to another. As such, you need to be really careful about which grass you’re using and what’s the right time to do it for your grass.
Grasses like perennial rye or any of the fescues will germinate quickly and grow tall in just 2-3 weeks so these grass types need to get mowed earlier than slower growing types like Kentucky Bluegrass, Zoysia, or Centipede.
Because quick growing grass types will need to be mowed earlier before roots are deep you will want to make sure you you are using a stronger mower that has a faster blade speed and make sure the blade is actually sharp. This will prevent the baby grass from getting uprooted.
I also advise my readers to consider applying a root growth stimulant product like RGS or CytoGro around seeding or shortly after germination to encourage more substantial root development as early as possible.
Desired Height Of Cut: For many grass types like Turf Type Tall Fescue up north or St. Augustine down lawn cut height is usually on the high side. If you’ve seeded a fescue lawn or sodded a St. Augustine lawn then it won’t make sense to do your first cut at 4-inches when your ultimate desired height up cut is four inches.
For tall growing grass types it may be best to wait until the grass is approaching 6-inches or when it is showing signs that it wants to lay over on itself and then cut it back to four inches so as to abide by the 1/3 rule.
On the other hand lawns like Zoysia, Perennial Rye, or even Bermudagrass can easily be maintained at one inch in height so you might not want to wait until these grass types grow much past two inches before you start cutting them back.
These lower cut grass types may require a reel mower to maintain the ultimate desired height of 1-inch and a reel mower will be the least likely to damage root systems or baby grass blades in their earliest states of maturity so this is where it pays to have the right equipment up front.
I personally don’t mow with reel mowers but I do know that the more blades on your reel the better. Without spending thousands on a fancy reel mower a good starter reel mower will be much lighter than gas-powered options and they will be much better for baby grass blades anyway.
If I were to buy a basic reel mower for low cut baby grass I’d go with this 7-blade Earthwise for the better cut quality and the low price.
Time Of Year: The time of the year is also another major thing that plays a role into your first cut.
If you planted grass seed in thee early Spring then the grass is going to be well suited for fast and efficient growth so you can easily cut the baby grass a little earlier and fully expect it to deal with the trauma of running the mower over it. The same can be said for the end of summer from late August through early October.
On the other hand grass that is sprouting going into summer (with the exception of warm season grass types) are going to struggle through the heat so you want to make sure you let those grass blades grow as long as possible before you stress them out with the first mow.
At the end of fall in the November timeframe it may also make sense to not cut the grass early either because all grass will naturally stop growing on it’s own this time of year as sunlight levels drop significantly and soil temperatures cool off.
The grass in mid-to late fall needs all the leaf blades possible for photosynthesis to put on the most substantial root systems possible before winter sets in.
Related: See this post for more answers to your lawn winterization questions.
How Long After Planting Grass Seed Should You Wait To Fertilize?
Many lawn care professionals recommend applying a starter fertilizer to the seed bed or overseeded lawn at time of sowing. In fact I always add fertilizer when I put seed down but I always choose to apply organics that break down and enter plant systems slowly so the timing is usually just right for seeds to germinate and grow for a week before they start using the starter fertilizer I apply.
Balanced fertilizers that include Nitrogen, Phosphorus, and Potassium with an emphasis on Phosphorus are key to the establishment of new grass from seed. My preferred starter fert at time of seeding is Lawn Box’s Fall Fix which is a 5-5-5 which I put down on at a high rate to get enough NPK into the soil prior to germination.
If however you didn’t apply fertilizer at time of seeding and your baby grass is just starting to grow then I advise applying a faster acting starter fertilizer that is also balanced.
Yard Mastery has a starter fert that is a 12-12-12 and is based on Ammonium Sulfate, a much faster acting source of nitrogen, Sulphate of Potash, an organic source of Potassium, and plenty of Phosphorus to help roots develop. I also love that micronutrients are included as well as a small bio-solid component that will help feed microbial life in your soil.
Even if you don’t opt for either of those products it is very important to add some fertilizer to your new grass soon after it starts growing so make sure to hit up your local big box store and get something because that will be better than doing nothing at all.
Rhizomatic and stoloniferous grass types need fertilizer to grow roots, shoots, and all of their lateral stems which bunch type grasses need plenty of nutrition to thicken up and fill in gaps in a lawn between sprouts.
If you are going into winter or into summer make sure to opt for a fertilizer that is heavy on P and K and has a touch less N because overgrowth going into periods of dormancy is usually a bad idea.
Don’t Forget To Mow With The Sharpest Mower Blades Possible
One thing you might want to keep in mind is that your lawnmower needs to have sharp blades when doing this job. As I mentioned above a few times newly germinated grass still isn’t mature and too much force (from a mower) can still actually uproot them.
If your lawn mower doesn’t have sharp blades expect a few grass plants to get uprooted when you mow resulting in unnecessary damage to your new turf.
Sharpening the blades yourself is really easy and fast if you own an angle grinder but you can also look into getting a blade sharpener drill attachment because most people have drills but only some people own angle grinders.
Here’s a simple mower blade sharpener bit meant to be used with your run of the mill hand drill. You can price out this cheap and handy accessory through this affiliate link.