# Overseeding this fall



## Danno99 (Aug 9, 2018)

Hey all,
This fall I will need to overseed quite a bit of my lawn.....I'm guessing about 2-3K. I've never had much luck with actually growing grass, so I want to ask a question or two.
The areas that need work currently have grass that's growing, it's just not growing very well. It's very thin in areas and a lot of it has a whiteness to it. My question is, before I seed those areas, the grass that's currently there has to be gone with first? I suppose I just can't throw topsoil on top of it and then throw done seed? If it has to be gone completely, do I just use something like Roundup first? Is there a better product to use? How long before I plant the seed should I use it?

Thanks!
Dan in NH


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## Harts (May 14, 2018)

Are you able post a few pictures?

It is not necessary to remove existing grass for an over seed, unless you have a weed issue or less desirable grass.

Take a look at the over seed guide. It will answer most, if not all of your questions.


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## Danno99 (Aug 9, 2018)

Pictures never really show the issue, I've found. Lets just say that it's not desirable. Should it be killed first? And how long after can I reseed?


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## Harts (May 14, 2018)

To be fair we can't comment on the current state of your lawn vis a vis reno vs over seed without seeing what it looks like. But certainly understand if you don't want to post pics.

If you are planning a reno, you really need to start now. Nuking your lawn needs to happen early on, giving you time to fallow and do a 2nd and maybe 3rd round (if necessary). It is possible to apply glyphosate and drop your seed the same day, but chances are you will miss a few spots and you'll end up with bad patches of existing grass

For example, someone who is planning seed down on Aug 15th, first app of round up would happen around now. Followed by fert and water to encourage existing weeds to grow. approx. 10-14 days later, a second round of round up would happen. Now you're into the beginning of August which gives you time to bring in any need soil to level the area.

Do you have your irrigation dialed in and know how you're going to water 3-5x per day? Have your sourced your seed?


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## Danno99 (Aug 9, 2018)

I'm going to try and post some pictures tomorrow. This spring I had some sprinkler heads replaced and now I'm pretty certain that I can hit every spot in my lawn now. 4 x per day @ 10 minutes is what I've done in the past, but I never got good results. It's always been way too sparse...maybe I'm just not putting enough seed? I think my soil is in good shape. I posted my results here somewhere and asked for comments, but didn't get any feedback.
Thanks for the advice. I'll try to post pix tomorrow.


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## uts (Jul 8, 2019)

Try posting the soil test here again.


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## Danno99 (Aug 9, 2018)

Here is my soil test and hopefully 3 pictures of weak spots in my lawn. The pictures may be deceiving because we're in the middle of a drought here in NH. My lawn has a continual cycle of going gangbusters in the spring, mowing twice weekly, but then when the heat sets in, you see what I get in the pictures posted.


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## ken-n-nancy (Jul 25, 2017)

Danno99 said:


> Here is my soil test and hopefully 3 pictures of weak spots in my lawn. The pictures may be deceiving because we're in the middle of a drought here in NH. My lawn has a continual cycle of going gangbusters in the spring, mowing twice weekly, but then when the heat sets in, you see what I get in the pictures posted.


I just commented on your soil test in a different thread, and then searched for other recent postings of yours to come across this one. It's not that I'm trying to stalk you, it's just that there aren't many other NH folks on here. Where specifically are you in NH?

It looks to me that your lawn is a typical northern mix. In particular, the fine fescue in a northern mix does great in New Hampshire climate during the spring and the fall. In the heat of July and August, however, the fine fescue goes dormant, which I think is much of your issue. There may also be a lot of _Poa annua_ and _Poa trivialis_ mixed in with your lawn, which will also turn brown in July and August.

I saw in a different posting that you have an irrigation system. Are you in a town that currently has watering restrictions, or are you still able to provide supplemental irrigation during dry spells?


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## g-man (Jun 15, 2017)

Do you have an irrigation audit done for your system? How many inches of water are you doing? How often?


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## bernstem (Jan 16, 2018)

My first thought is that your lawn looks very dry. I second an irrigation audit. It will also be important to know what your irrigation is doing during an overseed.

A couple more questions: 
- Can you post pictures of the lawn from farther back so we can see most of the front/back in a single picture?
- How much shade do you have?
- Do you know what type of grass you have?


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## Danno99 (Aug 9, 2018)

Hi all,
I will post more pictures tomorrow. When I've planted grass I've just gone with the New England Mix. I'm currently in Pelham NH and there has been a drought and limited watering. When it's ok to water, I usually go with an hour per zone twice a week. I've never done the tuna can thing, but I'm guessing that this is close to what I need.
I have zero shade. I cut down all the pine trees in an attempt to get rid of the moss in my lawn. I've put down over a ton of lime over the years but still get lots of spots here and there. 
Yes, I agree that the soil looks dry. Even with good weather the top of the soil is grey, but when I pull out a core, it looks really decent. 
When I post more pictures tomorrow I think it may be more obvious that I just don't have a thick enough lawn. You'll see some crabgrass, some white clover, some bald spots, lots of thin areas, etc. This is the reason why I posted on how to Overseed in the Fall. Thanks all, I'll post pix tomorrow.


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## Danno99 (Aug 9, 2018)

I've added a few more pictures. As you can see I have issues with weeds were my lawn meets the street, patches of clover, and thin bare spots. There is a watering ban at the moment and we're in the middle of a heatwave here. I haven't mowed in 2 weeks because the grass isn't growing. You might say that my grass is dormant and you're probably right, but it usually stays like this til the end of the season and doesn't bounce back. I really believe that I just need a thicker lawn for one, but always strike out when I try to seed in fall, around 2-3 week of September here.


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## Danno99 (Aug 9, 2018)

Here's my lawn on May 30th. I've given the dogs the few first feet for peeing, hence the bare spots, but you can see a deep dark green grass and then a lighter grass, and now 6 weeks later you can see what it looks like in my previous post.


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## g-man (Jun 15, 2017)

September is way too late for seeds in NH. I think the first week of August is more appropriate.


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## Harts (May 14, 2018)

+1. In the Toronto area we aim for the middle of August. I suspect your fall seedings have failed because there simply wasn't enough time for the grass to establish before winter.


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## Danno99 (Aug 9, 2018)

I've always thought that the time to seed in the fall is when the temperature changes from hot to cooler? Cool season lawns? The temperature here in the first week of August is going to be the same as it is right now, and that's brutally hot days?? I'm sure Toronto is cooler, but is there anyone here (ken-n-nancy) that live in this area that can confirm?
Also, I posted my soil results earlier, and can I just assume that my soil is ok and concentrate on other things?


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## doverosx (Aug 7, 2019)

+2 . I've had wild success and transformation in a short time simply by selecting the right time to seed. I seeded mid-august. The extra time that the last years warmer fall really helped grow things well and I took advantage of the N blitz.


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## Danno99 (Aug 9, 2018)

Ok, if you say mid august is the right time, then my questions still apply from my original post. If I could link it I would, but it might be further up here? I was asking if I needed to nuke unwanted grass before reseeding and what the timetable was?


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## edixon88 (Jun 18, 2020)

Danno99 said:


> I've always thought that the time to seed in the fall is when the temperature changes from hot to cooler? Cool season lawns? The temperature here in the first week of August is going to be the same as it is right now, and that's brutally hot days?? I'm sure Toronto is cooler, but is there anyone here (ken-n-nancy) that live in this area that can confirm?
> Also, I posted my soil results earlier, and can I just assume that my soil is ok and concentrate on other things?


Piggybacking on this question about overseed timing. I'm in NJ so I know I'm probably at least 1-2 weeks behind OP, but it stays close to 90 until Sept here, so I assume waiting until 1-2 weeks into Sept would be ideal?

_*Pasting OP's original question to bump it for him as well, not trying to hi-jack his thread:*_


Danno99 said:


> Hey all,
> This fall I will need to overseed quite a bit of my lawn.....I'm guessing about 2-3K. I've never had much luck with actually growing grass, so I want to ask a question or two.
> The areas that need work currently have grass that's growing, it's just not growing very well. It's very thin in areas and a lot of it has a whiteness to it. My question is, before I seed those areas, the grass that's currently there has to be gone with first? I suppose I just can't throw topsoil on top of it and then throw done seed? If it has to be gone completely, do I just use something like Roundup first? Is there a better product to use? How long before I plant the seed should I use it?
> 
> ...


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## M32075 (May 9, 2019)

I think using a northern mix seed is the problem. It's has a high count of PRG and fine fescue that is not going to look good in high heat or drought conditions. I would totally stop watering let nature take it's course. Let what ever can't survive the summer conditions die off you don't want it anymore. Come late summer de thatch and put down a quality tall fescue that can tolerate heat and drought.


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## bernstem (Jan 16, 2018)

You don't need to kill off the rest of the grass unless you want to change the grass type. You can cut the lawn low and seed into the short grass. If you have a lot of fine fescue going dormant in summer and then coming back in fall, you cannot kill it with roundup while it is dormant, but would need to wait for it to green back up for the round up to be effective. I still think that the problem areas of the lawn looks dry. Have you done an irrigation audit?


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## ken-n-nancy (Jul 25, 2017)

Danno99 said:


> I've always thought that the time to seed in the fall is when the temperature changes from hot to cooler? Cool season lawns? The temperature here in the first week of August is going to be the same as it is right now, and that's brutally hot days??


Well, there's a lot of different opinions about this (as you've surely already seen, both from reading elsewhere and reading here). The answer is also somewhat dependent upon the cool-season grass type being sown. Some cool season grasses germinate and develop very quickly (e.g. perennial ryegrass (PRG)), while Kentucky bluegrass (KBG) is infamous for being slow to germinate and very slow to develop.

The goal in choosing a fall seeding date is to have as much time as possible for the grass to develop before winter, without going so early that the baby grass suffers from summer stress right after germinating. PRG goes from seed to practically mature grass in about 4 weeks, while KBG doesn't really even approach being like mature grass until like 8-10 growing weeks, in my experience.

By the way, I think the real problem in New Hampshire with the onset of winter isn't as much the cooler temperatures in mid-fall, but the fact that we run out of daylight. Sept 21 is the autumn equinox. That means the day length and amount of sunlight available to the grass is the same as it was on the spring equinox (March 21). Nobody in NH would have dreamed of growing grass on March 21. Plus, the days rapidly get shorter in mid-September, and my experience is that by Oct 15th, there isn't enough sunlight left in New Hampshire for grass to grow much at all. (Just for perspective, on Oct 21st, daylight is about the same duration and intensity as it was on February 21st.) As a reference point, average first frost in my area is Sept 26th. Frost won't kill grass seedlings, but "average first frost" is a good indicator of when significant growth slowdown takes place. So, you really want as much time as possible for the grass to grow before that time. Seeding on Labor Day only gives about 3 weeks before Sept 26th. August 15th is about 6 weeks, which is a huge difference.

I've done two major renovations with KBG-only grass in New Hampshire. For the first one, I sowed seed on 9/9/2015. The grass didn't grow enough to need mowing before winter. It all seemed to survive, but was real slow to get started in the spring. My first mow was on 5/9/2016.

For the second one, I sowed seed on 8/24/2018. The extra 2.5 weeks made a huge difference. My first mow was on 9/21/2018, although that was only in the sunniest areas. The partly shaded areas were first mowed on 9/27/2018. Growth stopped around 10/22/2018.

My perspective is that what one really wants is for the grass to germinate at a time when the temperatures are just starting to get cooler. If you have irrigation, you can seed a little earlier, since you can regularly deliver water to the just-germinated grass seedlings, even if it is hot. Having to nurse the baby grass through a couple hot days in late August isn't too bad. (If we were talking about baby grass just germinating on July 1st, that's a whole different story.)

In my mind, August 15th would be a good seed-down date in Southern NH for a KBG lawn with irrigation. The grass should be well-germinated by August 25th, at which time days are getting markedly cooler, but there's still about 5 weeks left before average first frost and significant growth slowdown. That's enough time to let the grass develop enough to be mowed few times. August 25th is also still early enough that if there were washouts from the initial seeding, there's also hope that reseeded areas would develop enough to be mowed before winter.

Actually, I think the biggest challenge with a mid-August seeding of KBG in New Hampshire isn't the heat, but the likelihood of late August thunderstorms. Ideally, you want zero rain from seed-down until you have widespread germination of the grass. For PRG, that's only about 4 days. However, for KBG, that's about 10-12 days. Summer thundershowers aren't usually that many days apart in New Hampshire. I was very fortunate in my 2018 lawn renovation to have nearly zero rain from the day of seed-down for about 3 weeks.


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## dport (Oct 13, 2019)

bernstem said:


> You don't need to kill off the rest of the grass unless you want to change the grass type. You can cut the lawn low and seed into the short grass. If you have a lot of fine fescue going dormant in summer and then coming back in fall, you cannot kill it with roundup while it is dormant, but would need to wait for it to green back up for the round up to be effective. I still think that the problem areas of the lawn looks dry. Have you done an irrigation audit?


Any issue adding 1-3 inches of topsoil over existing grass and then reseeding? I don't have undesirable grass, but I have undesirable soil and I want to improve it. No need to kill off existing grass even in this scenario?


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## ken-n-nancy (Jul 25, 2017)

dport said:


> Any issue adding 1-3 inches of topsoil over existing grass and then reseeding? I don't have undesirable grass, but I have undesirable soil and I want to improve it. No need to kill off existing grass even in this scenario?


If you want to be sure that none of the existing grass survives the addition of the topsoil, such as because you are changing grass types, it would be wise to first kill off the existing grass. Other than that, adding topsoil over the existing grass and reseeding can work fine. This approach is actually commonly done by landscaping companies, even without first killing the existing grass.

However, there are some things to watch out for...

It is important that the existing soil surface not be compacted or a radically different soil type, or there can be problems with water accumulating on top of the old soil, making a soggy mess and causing trouble for root penetration into the old soil.
If the old grass is sufficiently thick, dense, or with a significant thatch layer, the subsequent decomposition of this organic matter when under the soil can rob the new grass of needed nitrogen.
If the old soil surface is not level, then even if the new soil is spread uniformly at constant density, subsequent settling of the soil can result in the new surface being bumpy or uneven.
If the old grass is not buried deeply enough, some kinds of grass (bermuda springs to mind) can grow back through a shallow layer of new soil. If you wanted to eliminate all the old grass, this may be a problem.

That said, the above approach is what was used for the regrading and installation of our new front lawn in 2013.


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## ken-n-nancy (Jul 25, 2017)

Danno99 said:


> ... My lawn has a continual cycle of going gangbusters in the spring, mowing twice weekly, but then when the heat sets in, you see what I get in the pictures posted.


It's really hard to tell from photos, but I highly suspect that the dormant (dead-looking) grass in the above photos is likely _Poa trivialis_. I would guess given your description of lawn history that there is also likely a significant amount of _Poa annua_ in the lawn. This probably isn't what you wanted to hear, but overseeding will not eliminate those grass types from your lawn, and if they are there now, _Poa trivialis_ and _Poa annua_ will continue to be present there next year, even after any overseeding you do this year.

This speculation on my part is also supported by the very light color of most of your lawn in the picture that you posted showing more of the lawn (quoted below). I think most of that light green, now brown (dormant) grass is _Poa trivialis_, as the spring coloring and recurring annual response to summer heat sure seems like _triv_ to me.



Danno99 said:


> ... you can see a deep dark green grass and then a lighter grass, and now 6 weeks later you can see what it looks like in my previous post.


Getting rid of _Poa trivialis_ isn't a challenge to be undertaken lightly. It's a lot of work and only really worth it if you're a fair bit "lawn crazy." An alternative is to just appreciate its advantages (low maintenance required, looks good in spring and fall, comes back in the fall even after appearing dead in the summer) and have it be part of your lawn -- at least it's green for half of the year. That approach works for most of my neighbors.


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## dport (Oct 13, 2019)

ken-n-nancy said:


> dport said:
> 
> 
> > Any issue adding 1-3 inches of topsoil over existing grass and then reseeding? I don't have undesirable grass, but I have undesirable soil and I want to improve it. No need to kill off existing grass even in this scenario?
> ...


Great, thanks for this. I have clay with occasional rocks as my main soil type. I did add some top soil last year, but looking to add even more this year. Appreciate the points on different soil types.


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## ken-n-nancy (Jul 25, 2017)

dport said:


> ken-n-nancy said:
> 
> 
> > It is important that the existing soil surface not be compacted or a radically different soil type, or there can be problems with water accumulating on top of the old soil, making a soggy mess and causing trouble for root penetration into the old soil.
> ...


There are things that one can do to mitigate a "soil horizon" from developing when putting new soil on top of a clay-rich soil -- getting deep penetration of large cores can help a lot. This is typically be done by a deep, widespread aeration. Personally, I think that standard approach could be potentially improved by taking really big, deep cores -- such as those with a ProPlugger set to a 6" depth. However, that's not a technique I've ever tested, as I don't have any first-hand experience with growing on clay soil here in sandy, rocky New Hampshire! However, the "really big cores" approach would seem to have merit. The idea is to allow water penetration down through the denser areas.


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## 603fish (Apr 16, 2020)

Just to add on to this as another southern NH guy planning an overseed. Mid-June I had 150 yds of fill brought in to level my backyard, and just had an irrigation system put in so my grass is in pretty rough shape. I plan on overseeding (90% TTTF/10% KBG) on the weekend of August 15th. There may be a few days that get too hot before Labor Day, but most likely not enough to kill a lot of the new grass. As @ken-n-nancy had mentioned, our problem will likely be thunderstorms washing away seed, so I'm planning on putting peat moss over the seed in the bare spots where washout might be an issue.


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## ken-n-nancy (Jul 25, 2017)

603fish said:


> Just to add on to this as another southern NH guy planning an overseed. ... As @ken-n-nancy had mentioned, our problem will likely be thunderstorms washing away seed, so I'm planning on putting peat moss over the seed in the bare spots where washout might be an issue.


Having done renovations of some portion of the lawn most years in the past eight years, washouts are definitely the biggest threat for lawn renovations in New England, presuming the use of automatic irrigation which is great for keeping just the surface of the soil moist.

Getting seven days of no rain after seed-down is a fantastic blessing (for an irrigated lawn) -- and one that we have basically no control over, so it's really just a matter of prayer!


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## Danno99 (Aug 9, 2018)

Hey all,
I appreciate all the great advice that I've gotten here.
I believe that @ken-n-nancy had the most sage advice as they live nearby, and while I guess I didn't want to hear that Poa trivialis is my issue.....I don't know anything about it, but I'm guessing it's a bitch to get rid off.....I will try and take care of what I can this fall and try to tackle Triv some other day.
Thanks again everyone.
Dan in Pelham NH


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## ken-n-nancy (Jul 25, 2017)

Danno99 said:


> ... I will try and take care of what I can this fall and try to tackle Triv some other day.


Dan, if you haven't already read it, a really good read is g-man's Cool Season Lawn Guide. It has all the info you need to make your current lawn the best it can be. In particular, the guidance for the Fall Nitrogen Blitz can really take a lawn to the next level in the fall.

After getting your current lawn in tip-top shape is the time to think about potentially renovating your lawn to change the grass type -- if at that time you think it's something you want to do, you'll have the experience to make it a success.


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