Clay and gravel and rocks, oh my!

alexislsApril 4, 2012

I am embarking on a major renovation of a garden that has been neglected for many years. And I'm faced with a particular challenge in one of the planting beds that is about 3x15 feet in size.

First I had to dig out the 6 dying Arborvitae - after I did that, it looked like I'd have nice soft soil to plant perennials in. Silly rabbit!

Turns out, there was only an inch of good soil that sat on top of a four inch layer of landscaping rock which sat on top of a sheet of visqueen. And it's likely been like that for multiple decades.

So I picked out more than 150 lbs of rock (basically everything larger than a nickel) and pulled up the plastic in shreds and then what did I find? Slick grey and yellow clay full of pea gravel. Ugh.

No wonder the trees were dying.

So now what? I have a truck load of good compost that I was planning to work in with a tiller before I discovered the clay/gravel. Should I proceed with mixing it in? Or should I dig out as much of the clay as I can, and replace it with a compost/topsoil mixture?

Since there aren't any plants in the bed, I figure now is the time to "do it right" but I'm not sure what that is.


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tropical_thought(San Francisco)

I am not sure, but I would say remove as much clay as you can. I have heard that from other people who have clay soil.
They say if you amend the top layer of clay you could have a bath tub effect in which the water will drain to the clay and then stop there rotting out the roots. Therefore, they suggest these things called french drains or you can make trenches or both.

    Bookmark   April 4, 2012 at 9:34PM
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Till the compost into the clay/gravel you have and that will, eventually, cahnge the soil you have into something workable. Digging out as much clay as you can will not do much, especially since the soils I have seen in Maryland are mostly clay, except along the shoreline.
You want to end up with soil that is abnout 6 to 8 percent organic matter. It may take 3 years to change that clay that holds too much water, but it will change.

    Bookmark   April 5, 2012 at 7:55AM
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tropical_thought(San Francisco)

Don't decide what to do until you search for clay soil here and the forum and read what people who have clay say about it. Kimmsr and I both have sand soil. I believe in hands on experience rather than following a set of classical rules on gardening. I think you can improve the soil that is clay with organic matter if you are going things like annuals, but if you are growing deeper rooted things like trees you need drains. Or you can also select plants that "like to grow in clay". You can search for a list of plants that like clay soil. Most of the heart break happens when people see a certain plant and they want that plant even though it is not right for their conditions. It is better to grow plants that like the soil you have then try to make a radical change to the soil. A huge change in your soil is costly and time consuming. You could start out with a few plants that like clay, then slowly improve the soil over time. Another big mistake is landscaping a whole garden at once. Try one bush or plant, see how it does, adjust and improve your soil, get another plant, until you reach your goal.

    Bookmark   April 5, 2012 at 8:29AM
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toxcrusadr Clay Soil(Zone 6a - MO)

You can go one way or the other here, and there are trade-offs to each. Amending the clay will eventually make it workable but it will take several years. It is less work and expense to do it that way. Or you could dig it out and replace it, more work and more expense up front but you get to the goal line faster. You'd have to find somewhere to get rid of the clay.

Is your whole yard like this under the topsoil? Gray and yellow clay? It does sound like horrid stuff.

The 'bathtub effect' that Tropical mentioned can happen with either approach. Whether you lighten the surface clay with amendments or replace it with a lighter soil, if there is clay underneath it may not drain very well. If you have plants that are sensitive to soggy roots, it's good to plant them a bit high and mound soil up around the root ball. If you're planting trees and shrubs make a wide dished hole instead of a deep one.

    Bookmark   April 5, 2012 at 10:13AM
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Thanks for your responses!

Fortunately, most of the soil in the garden while heavy, is quite workable and I think will be pretty good after a generous dose of compost. Since I'm starting with a clean slate, I'm going to till in about 8 inches of compost this year and then amend on top going forward.

It seems like it's just this spot that is particularly bad - I'm guessing that's why a previous owner just gave up and covered it with plastic and landscaping rock. Of course, that just starved the soil underneath and made it worse.

I think I'll try to get as much out as I can this year. While the clay could eventually be improved, all that gravel is going to be a problem forever.

As for planting, I'm going to start with an oakleaf hydrangea and a native wild senna and see how they do.

Wish me luck!

    Bookmark   April 5, 2012 at 11:01AM
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tropical_thought(San Francisco)

I am not sure about gravel. Some people like some gravel, it can improve drainage, if it is not too big or too small in size. If you take out some clay and the clay is mixed with gravel you will take out some gravel, right? Some companies sell gravel to amend clay soils, a clay soil conditioner.
Tur face is used on the garden web in some potting mixes like Al's gritty mix.

Here is a link that might be useful: Tur Face

    Bookmark   April 5, 2012 at 11:21AM
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toxcrusadr Clay Soil(Zone 6a - MO)

Gravel laden clay sounds like a pain in the butt. Don't blame you a bit for wanting to dig it out of there. :-]

    Bookmark   April 5, 2012 at 3:17PM
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LesIsMore1(4/5 - Colorado)

Deja-vu, totally. I'm in Colorado though, so my 'clay' might be alot different than yours. Still, I think you got the 'major renovation' part right...though you didn't specify a time frame. I take it, you have intentions to plant there this spring, or sometime within the next half-decade? If so, the way I went about it may not appeal to you very much.

In my case, the 'rocks' in there were the same 'landscaping rocks' that were in my driveway. (somebody else did this, it wasn't me) Initially, came to this soil fourm for help...(4 years ago, I think) that was before I found the 'landscaping rock layer' but that didn't phase me. By then I was well into corrective measures per advice I got here...which, the general consensus was, to start getting as much organic matter into that area as possible. Knowing it would take a long time, thats what I did. Kinda. The whole yard, front and back...had issues, so theres alway been plenty to work on - but this spot was the worst.

Technically, I did dig everything and all. (Still am, my long/narrow priblem area is 3x the size of its a process I deal with in phases...and, erm...its pretty hard on my shovels, I've broken a few in this area) But after I dig it out, I run it through my sifter...landscaoing rocks get dumped in the driveway, where... I have an eerie feeling, they originally came from, along some point in history.

Then whatever is left thats not rock, gets sifted again...more like, busted into chunks with heavy irin mallet...until it's eventually able to fall through 1/4" screen. After that, I sift compost (along with whatever other ammendments I think it might need) ...right into the same wheelbarrow as the clay. Mix it all around really well, ends up being rougly 40% compost. Dump it back in the hole where I got it. Mulch it, thick: 6-10 inches deep, chipped forest slash, aged. Fines sifted out first. Grab another couple buckets, sift, and repeat.

(I try to dig a 3-5 foot strip out all at once, load it all into buckets as I go. Takes a while, and by the time I'm sick of it...another batch of compost is about ready to come out of the to speak. Then I sift, and sift...until all buckets are empty again. I do between 10-15 feet a year, adding to the new retaining wall as I go...Not stopping till I get to the end.)

I know some people might think I'm crazy for doing it this way, there are much faster ways. But...I'm actually quite happy with the results I'm starting to see, this will be summer #4. This soil there isn't red anymore, its lighter, dark black...slightly porous, so actually drains now! But not too much...holds moisture too, just not like a bathtub would. I doesn't hurt my shovels anymore, or my dog's feet. (they insist on heavy machinery involved...just me and my dogs. Hands, paws)
, and an assortment of badly abused shovels, etc.)

But thats me, and I live on forested land. It's never been farmed, except fir me and my I tend to believe there's good minerals in this dirt, naturally I wanted ti keep it.

If that sounds like more effort than you wish to put forth? Think of this as a 'careful, do not try this at home' commercial. It's heavy labor. It's a... 'you'll never get the dirt out of those clothes where they aren't full of holes' kind of thing. Although... not a bad workout, which can be a bonus.


    Bookmark   April 6, 2012 at 12:40AM
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I have worked in gardens in Indiana (clay), Ohio (clay), Tennessee (clay), Georgia (clay), South Carolina (both clay and sand), Texas, (shale), and other places in the USA and correspond with people all over the world and have never found anything other that organic matter to be of help in making any soil better.
Organic matter mixed in clay opens up the pore spaces between the soil particles so water, nutrients, and plant roots can move around easier, as well as making the nutrients that get held onto by the clay soil particles more readily available to the plants.
Organic matter in sandy soils fills in between those soil particles so that moisture and nutrients are held in place for plants to use. The same thing happens in gravel soils.
The current issue of Readers Digest has an article, "13
Things your Landscaper won't tell you" that tells you to do the things I have been telling people to do far many years now.

    Bookmark   April 6, 2012 at 6:54AM
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toxcrusadr Clay Soil(Zone 6a - MO)

Clay really can be quite nutrient-rich, it just holds onto those nutrients so tightly that plants don't grow that well.
I'm hoping to see some richness from mine, although I've been working on it for 20 yrs and it still doesn't grown gardens like my friends in the silty river bottom can.

    Bookmark   April 6, 2012 at 10:17AM
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tropical_thought(San Francisco)

I found this link, I don't agree with everything it said, like the gypsum may or may not help, and I am not a fan of compost tea, when you can use real compost, which is much better. If you look around you can find similar opinions and "plants that like clay", surprising roses like clay, and so do coral bells, which I grow a lot. Even certain trees like clay. The university sites are good. I looked up trees that like clay and I got a list for Texas trees that like clay from the university, so you can find it your neck of the woods. Don't give up!

Here is a link that might be useful: clay soil guide

    Bookmark   April 6, 2012 at 11:21AM
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LesIsMore1(4/5 - Colorado)

I discovered something interesting the other day... speaking of clay.
Shopping for big rocks all last week, and noticed various types of clay on one of the pricelists. About fifty bucks for a yard of 'grey' clay, but almost eighty bucks for a yard of 'red' clay.

This seems strange to me...since red clay seems rather abundant in my area. Planning to call them next week, just to find out why the red stuff is so expensive... if it's about supply, or if the red is somehow more superior. Unless someone here knows...

Where I'm from (Red River of the North) the clay is mostly black/gray... but some of the most fertile farmland in the world is found up there, so I would have guessed that the red stuff would be cheaper. I suppose the word (clay) means different things to different people, depending on where you are...but is there such a thing as yukky clay? it that clay becomes yukky, in the absence of that organic matter that would make it easier to work with. Makes me wonder...

    Bookmark   April 15, 2012 at 4:25PM
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"Shopping for big rocks"??? You have to buy them??


    Bookmark   April 15, 2012 at 5:09PM
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I just planted an apple tree in a reverse "bathtub", I dug out the hole in an ocean of sandy gravelly glacial till and lined it with a material that is about 50% clay and silt, with some granite dust mixed in and a couple buckets of compost. I think the tree-ling is going to like that much better than sitting there gasping for moisture and nutrients.

    Bookmark   April 15, 2012 at 5:54PM
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tropical_thought(San Francisco)

pnbrown apple trees like sandy soil with organic matter that is well drainage. You are saying you took your good soil and made it bad? If you wanted to plant a mangrove tree it would like a reverse bath tub. This has to be another joke, of course, I can't really tell, but why work so hard if you soil is ideal sand to begin with for an apple tree. It all depends on what you want to grow.

    Bookmark   April 15, 2012 at 6:24PM
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tishtoshnm Zone 6/NM

In my area, apple trees grow just fine and dandy in clay. Growing them in sand would be a huge mistake as the clay helps to stabilize them better in the high winds and since my area is dry, the clay holds onto the water better.

For the OP, if that was my spot, I would double dig it, sieve out as many rocks as possible and amend it according to the needs of the soil. Since my clay is alkaline, for me that would be with peat moss, gypsum, and lots and lots of compost. Good luck.

    Bookmark   April 16, 2012 at 1:01PM
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toxcrusadr Clay Soil(Zone 6a - MO)

pn, I think I follow your logic: I'm guessing the sand and gravel drains SO well in your area, AND maybe you live in a dry area so you don't get that much rain to begin with. So you added a little clay and silt to give the soil around root ball a chance of retaining water and nutrients a bit better.

It depends not only on 'what you want to grow' but your local conditions, and I've read enough of your posts that I am pretty sure you know what you're doing. :-]

Regarding Les's post just before that, I can't figure out why anyone would pay good money for red clay in the first place, unless they're making bricks. Heck, I've got some clay here I'll GIVE you if you'll come get it! I hate the stuff.

    Bookmark   April 16, 2012 at 5:18PM
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