Aeration core depth and seed

Discussion in 'Turf Renovation' started by RigglePLC, Nov 5, 2016.

  1. RigglePLC

    RigglePLC LawnSite Fanatic
    Messages: 14,939

    A test was devised to compare aeration hole depth and seed germination. Depths of 1, 2, and 3 inches deep were compared. Four types of seed were sown: bluegrass, perennial rye, tall fescue, and fine fescue. The test was conducted indoors at about 65 degrees. Purchased, screened, loam topsoil was packed in a deep flower pot. A 3/4" soil probe was used to make the "core" holes. Unfortunately after seeding and watering, the holes tended to fall inward when watered in the next day or two. The holes were almost invisible after two days.

    At 8 days, rye was the first to emerge and tallest, a maximum of 3 inches tall from the one-inch deep core, 1.87" tall from the 2-inch depth, and 1.25 at the 3" depth.
    Tall fescue was second at 1.5, .37 and .37" tall.
    Fine fescue was third at .75, .75, and .75" tall.
    Fourth was Kentucky bluegrass. Surface applied was at .5". One-inch deep emerged to about .25" tall. Only a few shoots emerged. There were no signs of emergence in the 2-inch or 3-inch deep bluegrass cores.

    Last edited: Nov 5, 2016
  2. KLC Lawns

    KLC Lawns LawnSite Senior Member
    Messages: 294

    I do not over seed where I'm at but am always glad to see some research and helpful info posted. So much politics and " what should I do" topics on here that I'm always interested in learning something in depth on this site.
    Rick Engasser and sjessen like this.
  3. Methodical2

    Methodical2 LawnSite Member
    Messages: 112

    With respect to the KBG, wouldn't the fact that it takes upward of 3 weeks to germinate affect this test. I think using all of one type of grass seed type measured at the different hole depth would tell a better story. Thoughts.
    Wazee303 likes this.
  4. RigglePLC

    RigglePLC LawnSite Fanatic
    Messages: 14,939

    Thanks, Methodical. You are quite right, of course. 8 days is a short test. I was happy to see that at least some of the Kentucky bluegrass germinated at only 8 days. (Surface sown.) I am sure that it would take much longer to reach the surface if the bluegrass were buried at 2 or 3 inches deep. Perhaps this would add still more weeks to the already slow emergence time for bluegrass germination.
    Still, 8 days is a good sign. For the typical customer--however, they are probably not going to notice sprouts that are a half-inch tall.
    Is anyone else willing to try this over the next few weeks?

    What happens under your soil conditions?
    Last edited: Nov 20, 2017
  5. KerbDMK

    KerbDMK LawnSite Bronze Member
    Messages: 1,204

    I’ve always had a difficult time understanding the physical mechanisms involved in getting seed to grow out of plug style aeration holes. It always looks to me like most of the grass that sprouts out of the holes is located around the edges of the holes and not in the middle. I suspect those seeds are clinging to the side of the hole.

    It seems to me that any seed that falls to the bottom of the hole would have little chance for survival, since most seeds that end up buried deeper than two times their length will fail to survive.

    Then there are all the variables that go into how the seeds and soil from the plugs get into the holes. Some of the seed will fall directly into the holes but I think most are moved into the holes by wind and water. How and when the seed, and maybe some of the soil, finds its way into the hole will determine its chances of survival. All of that just seems to happen by chance.
  6. Methodical2

    Methodical2 LawnSite Member
    Messages: 112

    @KerbDMK I agree that's why I used to aerate and dethatch (this broke up the plugs) when we first moved into our home years ago and I did it spring and fall for the first few years until I got the lawn thick and healthy, however I found dethatching and seeding to give the best germination. I feel that scratching and loosening the soil allowed better seed to soil contact. I know my theory goes against the norm as most professionals suggest you aerate and seed. Here's my thought as to why they suggest aerating vs. dethatching is because it's less work; it requires no raking up the thatch (if any) or dead grass and they don't want to risk potentially damaging the existing lawn (aerating won't do this). I'm sure there are other reasons, but those are what I think are the top ones. They can aerate quickly, seed, fertilize and be done with it - I've seen them do it on my neighbor's lawn. I know many believe dethatching tears up the yard, but I found that to not be totally true from those years of dethatching; it actually opened up the lawn and exposed the soil better. My neighbors were even surprised that my lawn didn't look tore up after seeing all the dead stuff that was bagged after dethatching.

    Mind you this was my first home and I was new to all of this and the KBG was a tough grass to maintain without sprinklers, crazy summer weather, bad soil left by the builder with all kinds of crap buried in the lawn and heavy clay soil.

    Just One Man's Opinion.
    Last edited: Nov 20, 2017
    KerbDMK likes this.
  7. KerbDMK

    KerbDMK LawnSite Bronze Member
    Messages: 1,204

    You make many good points there. Seed to soil contact is the key, and dethatching and aerating will expose more soil than just aerating.

    I agree that the reason more people just do the aeration and overseed is because it’s a quick, easy, and an economical way to do it for both homeowner and LCO. There are lawns like fine fescue that need to be aerated rather than dethatched because dethatching rips the fine fescue right out of the ground.

    LCO’s could offer to dethatch and overseed too and that would work just fine for many cool season lawns, but aerating and overseeding has just become the accepted norm. Around here all the LCO’s are doing a semi-dethatching in the spring and aeration and overseedings in the fall. It’s what works and sells well for them and that’s what they offer their clients.
  8. RigglePLC

    RigglePLC LawnSite Fanatic
    Messages: 14,939

    Very good points Methodical and Kerb.
    It would be interesting to compare germination after aeration, with germination having the cores removed.
    And with germination having the cores applied, but no holes.
    Just count the number of new germinating sprouts on one sqft.
    You are not busy this week, right?

    I think you are right. Cleaning up a few hundred pounds of dead grass after a dethatch operation or vertical mow is a lot of labor hours. Aeration is quicker. And some guys just love machines--even if they are expensive and costly to repair.

    Good point about the seed catching on the sides of the aeration holes. Suppose as a test, one could send some seed to the bottom of the hole, through a glass or plastic tube.

    If you are making money with aeration--fine.
    If you prefer applying double seed, its quicker.
  9. KerbDMK

    KerbDMK LawnSite Bronze Member
    Messages: 1,204

    I’ve been giving the idea about the seeds seeming to always congregate along the edge of the holes some more thought, and I’m starting to think that it’s the surface tension of the water as it seeps into the soil that draws the seed to the edge of the hole. Grass seed floats and maybe this is what helps to keep the seed from being buried too deeply.
  10. Patriot Services

    Patriot Services LawnSite Fanatic
    Messages: 15,802

    Brother, I've been asking this same question myself for years. Aeration is not the proper prep for seeding. I use slit seeders period. Puts the seed at proper depth in near perfect distribution. I don't even dethatch as that provides protection and moisture retention. I don't aerate our sandy soil anyways and irrigation damage is almost guaranteed. We do a lot of hybrid Bermudas, Zoysia and even Bahia this way. Cuts way down on labor and as I said the coverage is always excellent.

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