Introduction
There seems to be a lot of interest here on the forums for an overseed guide so I'm going to give it my best shot. Keep in mind, this is primarily for TTTF or PRG lawns. Some of these ideas will work with KBG but that's a totally different animal so someone with more KBG experience could do a separate write up for that. I'm no professional and this guide is comprised of techniques I've tried over the years and has worked very well. Every lawn is a little different so slight adjustments or changes might need to be made for each individual situation but this should be really close for anyone overseeing a TTTF or PRG lawn.
First let me say this. One of the most important things you can do for your lawn is a soil test. I won't go into a lot of detail here but if you're going to put effort into making your lawn better this is the easiest and cheapest way. If the soil does not contain the proper balance of nutrients nothing else you do will make it any better. Guessing here is only going to cause pain, suffering and bad results.
Seed selection: I start with good quality seed that is 100% free of weed seeds. No sense in starting out with weeds. Yes, it will cost a little more but will be well worth it come next spring when you have a beautiful weed free lawn. There are several well known companies that sell [https://thelawnforum.com/viewtopic.php?f=9&t=9400]quality seed[/url]. I've had good luck with The Hogan Company. With coated seeds, you are paying more for less seeds (50% seeds/filler), so must of us avoid them.
Overseed:
First thing to do is cut the existing grass low. The term "low" is relative to the HOC where you normally keep your lawn. During the summer months I stay between 4" to 5" so for me 2.5" to 3" is what I consider low. If you keep your lawn at 3" then you may want to go down to 1.5" for the overseed. The idea here is to throw the existing grass into shock which will slow or stop growth for a week or two. This will give the seeds time to germinate and get some height so it is able to compete with the existing grass. If you have a bagger you can do this in a single cut bagging and removing the clippings. Without a bagger, you will need to make multiple passes lowering the cut with each pass until you reach the desired height. Hopefully you know your mower well enough to know how much grass it can remove at once without leaving excessive clippings. At this point the grass will likely be pale and stemmy looking. That's ok because in a few weeks it's going to look amazing!
Aeration: Some folks don't believe in aeration while others go completely overboard with it. If the soil isn't compacted then you probably don't need to aerate. I have had certain areas where the soil was easily compacted. Typically what I do with those areas is make one pass with the aerator, then spread a light coat (1/4" to 1/2") of compost, then make two more passes with the aerator. Outside of extremely bad cases this make a huge difference with problem areas. It's been years since I've aerated the entire lawn. Instead I only do the problem areas.
Fertilizer: There is really no need to drop fertilizer at the time of an overseed, especially anything with nitrogen. Everything the new grass needs for the first few weeks of life is contained in the seed. At this point you have cut the existing grass low in an effort to slow its growth so the new seedlings can catch up. Adding nitrogen at time of seeding will give the existing grass a boost causing it to outgrow and try to choke out the new seedlings. Don't do it! Even Milorganite can cause this issue. The only exception would be organics such as alfalfa or soybean meal which take two to three weeks to kick in and cause top growth. I do add 0-25-25 at time of seeding. Normally I do 1 lbs of 0-25-25 per 1k at time of seeding which helps promote root growth. This is fine, just don't put down any nitrogen. If your soil test shows that P and K are high skip this step.
Seeding: The typical overseeding rate of TTTF and PRG is 4lbs per 1k. What I do is first hand seed any small bare spots and then use the spreader. I will completely skip any areas where the grass is already thick. No sense in putting seed down where you don't need it. I use one of those over the shoulder bag type spreaders. With this spreader I can easily regulate the amount of seed coming out. I go a little heavier in really thin areas and lighter in the areas that don't need as much. The key is to maintain a good thick turf but not so thick that it chokes itself out. As mentioned at the beginning, a good quality seed is best.
Pressing the seed into the soil: Seed to soil contact is extremely important to good germination. After spreading your seed it's time to go over it and press it into the soil. If you have a really small lawn, get the family out and have them walk over the newly seeded area. For larger lawns, you can rent a lawn roller and go over the area with that. You can also go over the lawn with a riding mower using the tires to press the seed in. The goal here is to press the seed into the soil no matter how you do it.
Water: In order for seed to germinate it must have sunlight and moisture. Moisture is the key word here. You don't want to drown the new seed. Watering lightly anywhere from 2 to 5 times per day just enough to keep the seed moist. Temps, humidity, and the amount of direct sunlight on the seeded area will effect how quickly the seed and soil dry out. If you get this right and keep it moist you should start seeing germination in 5 to 7 days. Keep watering this way for 2 weeks which is when germination should be complete.
First Mow: Following this guide your first mow should be about 2 weeks after seeding. In my experience, the new grass is up to about 3.5" at this point and I will cut it back to 3". Make sure your mower blade/blades are razor sharp. While the new seedlings are about as tall as the existing grass the roots are still developing and can be quite shallow. The first cut is going to pull up a few seedlings but a dull blade will pull out even more. Also be very careful when making turns as the slightest mistake can do damage. This is also the time to back off on watering. Slowly wean the new grass off by watering once a day to every 3 or 4 days depending on temps.
Fertilizer: After the first cut is when I slowly start fertilizing. For this I use urea. It's relatively inexpensive and by this time the temps are generally cool enough that you don't have to worry about burn. First and second app is 1/4lbs nitrogen per 1k a week apart. Each app has to be watered in with at least 1/4" of water. Mow as needed. After the first two nitrogen apps you can incease it to 1/2lbs nitrogen per 1k every two weeks.
I hope this helps some folks out and prevents some of the common mistakes. Trust me, most of what I've learned was done the hard way with a ton of mistakes and some of them were pretty costly.
There seems to be a lot of interest here on the forums for an overseed guide so I'm going to give it my best shot. Keep in mind, this is primarily for TTTF or PRG lawns. Some of these ideas will work with KBG but that's a totally different animal so someone with more KBG experience could do a separate write up for that. I'm no professional and this guide is comprised of techniques I've tried over the years and has worked very well. Every lawn is a little different so slight adjustments or changes might need to be made for each individual situation but this should be really close for anyone overseeing a TTTF or PRG lawn.
First let me say this. One of the most important things you can do for your lawn is a soil test. I won't go into a lot of detail here but if you're going to put effort into making your lawn better this is the easiest and cheapest way. If the soil does not contain the proper balance of nutrients nothing else you do will make it any better. Guessing here is only going to cause pain, suffering and bad results.
Seed selection: I start with good quality seed that is 100% free of weed seeds. No sense in starting out with weeds. Yes, it will cost a little more but will be well worth it come next spring when you have a beautiful weed free lawn. There are several well known companies that sell [https://thelawnforum.com/viewtopic.php?f=9&t=9400]quality seed[/url]. I've had good luck with The Hogan Company. With coated seeds, you are paying more for less seeds (50% seeds/filler), so must of us avoid them.
Overseed:
First thing to do is cut the existing grass low. The term "low" is relative to the HOC where you normally keep your lawn. During the summer months I stay between 4" to 5" so for me 2.5" to 3" is what I consider low. If you keep your lawn at 3" then you may want to go down to 1.5" for the overseed. The idea here is to throw the existing grass into shock which will slow or stop growth for a week or two. This will give the seeds time to germinate and get some height so it is able to compete with the existing grass. If you have a bagger you can do this in a single cut bagging and removing the clippings. Without a bagger, you will need to make multiple passes lowering the cut with each pass until you reach the desired height. Hopefully you know your mower well enough to know how much grass it can remove at once without leaving excessive clippings. At this point the grass will likely be pale and stemmy looking. That's ok because in a few weeks it's going to look amazing!
Aeration: Some folks don't believe in aeration while others go completely overboard with it. If the soil isn't compacted then you probably don't need to aerate. I have had certain areas where the soil was easily compacted. Typically what I do with those areas is make one pass with the aerator, then spread a light coat (1/4" to 1/2") of compost, then make two more passes with the aerator. Outside of extremely bad cases this make a huge difference with problem areas. It's been years since I've aerated the entire lawn. Instead I only do the problem areas.
Fertilizer: There is really no need to drop fertilizer at the time of an overseed, especially anything with nitrogen. Everything the new grass needs for the first few weeks of life is contained in the seed. At this point you have cut the existing grass low in an effort to slow its growth so the new seedlings can catch up. Adding nitrogen at time of seeding will give the existing grass a boost causing it to outgrow and try to choke out the new seedlings. Don't do it! Even Milorganite can cause this issue. The only exception would be organics such as alfalfa or soybean meal which take two to three weeks to kick in and cause top growth. I do add 0-25-25 at time of seeding. Normally I do 1 lbs of 0-25-25 per 1k at time of seeding which helps promote root growth. This is fine, just don't put down any nitrogen. If your soil test shows that P and K are high skip this step.
Seeding: The typical overseeding rate of TTTF and PRG is 4lbs per 1k. What I do is first hand seed any small bare spots and then use the spreader. I will completely skip any areas where the grass is already thick. No sense in putting seed down where you don't need it. I use one of those over the shoulder bag type spreaders. With this spreader I can easily regulate the amount of seed coming out. I go a little heavier in really thin areas and lighter in the areas that don't need as much. The key is to maintain a good thick turf but not so thick that it chokes itself out. As mentioned at the beginning, a good quality seed is best.
Pressing the seed into the soil: Seed to soil contact is extremely important to good germination. After spreading your seed it's time to go over it and press it into the soil. If you have a really small lawn, get the family out and have them walk over the newly seeded area. For larger lawns, you can rent a lawn roller and go over the area with that. You can also go over the lawn with a riding mower using the tires to press the seed in. The goal here is to press the seed into the soil no matter how you do it.
Water: In order for seed to germinate it must have sunlight and moisture. Moisture is the key word here. You don't want to drown the new seed. Watering lightly anywhere from 2 to 5 times per day just enough to keep the seed moist. Temps, humidity, and the amount of direct sunlight on the seeded area will effect how quickly the seed and soil dry out. If you get this right and keep it moist you should start seeing germination in 5 to 7 days. Keep watering this way for 2 weeks which is when germination should be complete.
First Mow: Following this guide your first mow should be about 2 weeks after seeding. In my experience, the new grass is up to about 3.5" at this point and I will cut it back to 3". Make sure your mower blade/blades are razor sharp. While the new seedlings are about as tall as the existing grass the roots are still developing and can be quite shallow. The first cut is going to pull up a few seedlings but a dull blade will pull out even more. Also be very careful when making turns as the slightest mistake can do damage. This is also the time to back off on watering. Slowly wean the new grass off by watering once a day to every 3 or 4 days depending on temps.
Fertilizer: After the first cut is when I slowly start fertilizing. For this I use urea. It's relatively inexpensive and by this time the temps are generally cool enough that you don't have to worry about burn. First and second app is 1/4lbs nitrogen per 1k a week apart. Each app has to be watered in with at least 1/4" of water. Mow as needed. After the first two nitrogen apps you can incease it to 1/2lbs nitrogen per 1k every two weeks.
I hope this helps some folks out and prevents some of the common mistakes. Trust me, most of what I've learned was done the hard way with a ton of mistakes and some of them were pretty costly.
