How To Overseed A Lawn: In The Fall or Any Other Time Of Year

By Brian Mounts | Aug 19, 2021
how to overseed a lawn

Overseeding a lawn in the fall is one of the best things you can do for the health and thickness of your turf. The fall is the optimal time of year to grow grass from seed and it’s the best time of the year to push new growth in your existing grass.

The steps outlined below are going to work for an overseeding project at any point of the growing season, Spring, Summer, or Fall but if you can wait until late August to late September then your chances for success are going to be greatly increased.

With that being said overseeding a lawn is fairly straight forward.

To properly overseed a lawn you want to spread grass seed evenly across your lawn space ensuring you get seed-to-soil contact. Apply starter fertilizer and cover with peat moss to retain moisture and protect the seed from wind and animals. Lightly watering the seed a few times a day is all that is needed to get it to germinate and depending on the grass type this can happen in less than 1-week.

However there are many optional steps that you can take to improve germination rates, improve even coverage, encourage deeper rooting, and stop animals from disturbing the seed bed.

I’d like to cover those optional steps and provide some extra detail on how I overseed for nearly perfect germination…but first I’d like to show yo a video I made on this topic which I’ve embedded below.

In the video you saw every major step I took to overseed an existing lawn but there was a lot of detail that I wasn’t able to cover. Although the space I demonstrated was small all steps I took are applicable to large lawn areas as well.

Overseeding Q&A – Yes! You Can Grow Grass Reliably From Seed

Have a close look at the frequently asked overseeding questions below to learn a lot more about overseeding an existing lawn successfully.

How Early In The Fall Can You Overseed? – For cool season lawns best practice is to overseed at least 6-8 weeks prior to average first frost dates. Many cool season grass types like Perennial Rye, Bluegrass, and the Fescues can withstand mild frosts even in the seedling phase but they will grow better and stronger when started early. Many northern locations can successfully overseed as early as mid-August just fine.

How Late In The Fall Can You Overseed? – You can overseed as late as temperatures stay high enough to support germination. I have sprouted cool season grass seed in soil temperatures as low at 45 degrees which can be found in many norther lawns well into late October. The later into the season it gets the fewer sprouts you’ll get and the thinner the grass will be going into winter but if you experience mild winters this may be better than dormant seeding or Spring seeding.

Can You Just Sprinkle Grass Seed Onto The Lawn? – You can just put grass seed directly onto the lawn and walk away but your germination rate will be extremely low without preparing a seed bed, watering deliberately, protecting the seed, and fertilizing the new grass. In most cases sprinkling grass seed onto the lawn without taking any other steps is a waste of money but in the right climate this might work just fine. Places that get regular rain or drizzle in the fall, especially those places with humid air, may fair better with lazy seed sowing.

Is Overseeding A Lawn Without Aeration A Bad Idea? – If you choose to take many of the optional steps to over-seed your lawn but ultimately don’t want to use liquid aeration or run a mechanical core aerator over it then your overseeding project will likely do just fine, but with one issue – rooting will be weaker. Both liquid and core aeration allow for grass roots to reach deeper into the soil resulting in grass plants that are stronger and better able to resist stresses throughout the year.

Can You Walk On The Lawn After Overseeding? – Yes, you can walk on the lawn and the new grass will still sprout and grow just fine. Your footsteps may damage some of the new seedlings but not enough to make a big difference over the long run. Walking on the seedlings may also disturb their placement on the seedbed resulting in slow germination of the disturbed seeds. For this reason it’s best to not walk on the lawn during the germination period if you can avoid it but if you have to walk on it it will be fine for the most part.

Can You Use Too Much Grass Seed? – You should always follow label rates for seeding new or existing lawns. Each grass type will require a certain amount of space between seeds and if you apply too much seed then the sprouts will be crowded and will compete for space, nutrients, and water resulting in a weaker lawn. As the lawn matures and thickens up naturally too many grass plants can be wasteful because the weakest will usually die off leaving you with a somewhat bumpy lawn. Thin even seed spread is what you want; there is no need to over sow grass seed.

Will Overseeding Kill Or Prevent Weeds In The Lawn? – Overseeding a lawn will not immediately kill off weeds but as summer fades and cooler fall temperatures take hold new grass will fill in bare spots on the soil where weeds used to be. In subsequent year there will be less space for weeds to grow and you will likely have fewer weed in the yard and more desirable turf grass.

Do You Have To Rake In Grass Seed? – You should always rake in grass seed if you haven’t taken the time to dethatch your existing lawn prior to spreading seed. The reason is that raking helps improve seed-to-soil contact which is necessary for seed germination. Dethaching is a more aggressive form of raking and when done prior to seeding will create grooves in the existing lawn, thatch, and soil that grass seed can settle into. Dethatching is best but if you can can’t run an electric dethatcher over your lawn space raking in the grass seed is your next best alternative.

How Can I Make Grass Seed Germinate Quicker? – When overseeding a cool season lawn you will always get fastest germination rates at the end of summer when soil temps are the highest. To improve the speed of germination at this time of year you’ll want to sow your seed onto a deeply watered surface and then cover with pre-moistened peat moss or coconut coir, products that are very good at retaining moisture. Lastly, covering the entire area with crop cover will limit evaporative moisture loss due to wind and result in stable moisture levels in your seed. When seeds stay evenly moist and undisturbed by foot traffic form people or animals they will germinate quicker.

What Grass Seed Grows The Quickest From Seed? – If you are seeding a new lawn or overseeding an existing lawn and short on time then planting Perennial Rye will give you the fastest grass sprouts of all grass types. In ideal situations it’s not impossible to see baby grass in as little as three days. For warm season climates Bermuda grass can germinate in just under a week and establish itself in another 10-20 days depending on soil temperatures.

Do You Have To Overseed Every Year? – The vast majority of people do not need to overseed their lawns every year. Only a select few grass types really need to be overseeded annually. Most fescues and annual rye grasses benefit from annual overseeding and damaged Kentucky bluegrasses can benefit because they don’t spread into weak spots fast enough to recover on their own. Most warm season grass types are rarely overseeded. Exceptions to this rule might be Zoysia and Centipede which are both slow growers however thin spots of these grass types can usually be repaired through better cultural maintenance and fertilization.

Do You Overseed Or Fertilize First? – For fast germinating grass varieties like Tall or Fine Fescues and Perennial Rye it’s best to overseed the lawn and fertilize on the same day. This is because you want to put grass seed down and have the fertilizer become plant available in the soil at the same time. For slow to germinate grass varieties such as KBG, and most warm season varieties it can be beneficial to overseed and then wait a few extra days before applying starter fertilizer. It’s never a good idea to fertilize ahead of overseeding because the fertilizer will simply push new growth from existing grass and a lot of the fertilizer will either be used up (or lost) by the time germination roots finally reach into the soil from your seed.

Do You Overseed Bermuda or Zoysia Grass Types? – Usually you don not need to overseed Bermudagrass or Zoysiagrass lawns because the grass types are capable of spreading horizontally and filling in bare spots in a lawn on their own. If large damage occurs and/or a lawn owner does fertilize their lawns enough then overseeding once every 2-4 years may be acceptable. For large blemishes in a warm season lawn overseeding can be much more difficult of a repair compared to installing sod in the damaged areas – for this reason many owners of warm season grass types never overseed and instead fertilize throughout the year and repair lawn spaces with sod as needed.

There’s So Much More To Lawn Care

If you are overseeding then you probably care a lot about your lawn just like I do.

Take a look at my other lawn care guides and make sure to see my full guide to growing grass from seed to make sure your projects in the lawn are successful!