how deep?

atoner – posted 30 July 2003 18:16

How deep does the soil need to be free of rocks and compacted soil to allow good grass growth? The depth of a core aerator, around 4″? I’m getting ready to seed a 1-year-old yard and need to know if I should really tear it up or just rely on the aerator to show me the way.

Thanks,Adam

Dchall_San_Antonio – posted 31 July 2003 10:40

If you have 4 inches of anything on top of rocks, you’re doing better than many people. If you have 4 inches of rocks on top of larger rocks, then I would call in the scrapers to have it replace with a landscaper’s mix of sand, clay, and humus.

I’m a believer that you can work with anything except rocks. Clay, sand, and everything in between is workable with organic methods and materials.

I also believe that if you concentrate on building great soil, your turf will look better than you expect with maybe a little hand work needed on the weeds.

How do you build great soil? I think these three things are the keys. I’ll list them in order of importance.

Begin to water deeply and infrequently. Deep watering develops deep, drought resistant roots. It also opens up soil “pores” that allow water to move even deeper into the soil at the next irrigation.

Mow the grass high. I always suggest welding the mower deck at the highest setting because there is never a reason to scalp a lawn. Welding it there prevents the well-meaning neighbor kid from coming in and dropping the deck on you while you’re on vacation. Tall grass develops deep roots, too. It also shades out weed seeds and shades out weeds that require full sun. None of this applies if you want to have bermuda, bent, or centipede grasses.

Fertilize with protein based organic fertilizers. Compost is not a fertilizer. Corn meal, alfalfa pellets, cottonseed meal, coffee grounds, corn gluten meal, soy meal, canola meal, milo meal, and even wheat flour are all protein based organic fertilizers. These materials feed the soil microbes and allow them to develop the soil structure and tilth you are looking for in your soil.

When you use the first two methods and throw in the organic fertilizer, you get a super improvement to your soil that will give you a super improvement in your turf.

As a caveat to the above, if you use chemical pesticide, herbicide, and/or fungicide on the lawn, will negate the value of using the organic fertilizer. On the plus side, if you use the organic fertilizer, you may not need the herbicide, pesticide, or fungicide. If you think you do, then write back.

atoner – posted 31 July 2003 12:03

Thanks for the reply. My yard was a bit odd this year. About half of it grew good grass (mostly bermuda) with roots that extended inches into the clay. Other parts of the yard, including most of the back, didn’t grow grass well at all. I dug down there and found that the clay is very hard just an inch or less into the soil, and is even worse when dry. It seems the roots just didn’t grow deep, which is why the grass in the back is now not growing and in fact dying.

The yard is free of rocks in at least the first inch of soil. Beyond that, some areas are clear down to 4 inches or more, but some areas have a lot of small rocks or bigger rocks. I’m doing some manual core aerating in the yard, mainly to find the big rocks so I can pull them out.

The problem with the back yard is that the soil is so dense that water doesn’t soak in, and aerating is impossible unless the soil is wet.

Dchall_San_Antonio – posted 04 August 2003 13:18

Since you have dense clay, then you cannot water deeply, yet.

Since you have bermuda, you should be mowing as close as 1/2 inch, so mowing high is out.

You’re left with organic fertilizer. If you could actually mulch parts of your soil with an inch or so of compost every few months, that would really go a long way to softening the clay. I’ve read about a guy who swore on the use of plain sawdust to soften his clay. He started out with cerami quality clay and 12 years later had soil he could sink his arms into the elbows. I don’t expect you to go 12 years, certainly the guy was able to grow things much earlier than 12 years. The only point of that is that organic matter ON TOP OF THE SOIL will do everything you want, sooner or later.

Sawdust is well known in the organic community as a horrible mulch. Well, this guy proved that adage wrong. It depends on what you’re trying to do with it. He just kept his veggie beds covered year round with an inch or two. He never tilled it in, just let it sit on top.