mattie g
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Amending Soil - Reducing Heaviness of Red Clay-ish Soil

Firstly...if this is in the wrong sub-forum, I wouldn't be upset if a mod moved it. So move away, if needed!

Mainly, though, this is a question about amending my soil to ameliorate its heaviness (it contains quite a bit of red clay). What I'd like to do is get a top layer (6" or so) that is somewhat similar to the soils that people shoot for in raised beds. Unfortunately, with the garden landscaping laid out the way it is, I can't make raised beds, but I do have sections cordoned off for my vegetable gardening use. These areas are separated from the rest of the ladscaping by bricks that have been pushed partially into the ground.

Right now, the top couple inches of the soil is fairly loamy, but once you dig down below that, it gets pretty hard. My tomatoes and peppers have done pretty well for the most part, but that's partially due to the fact that I fill my (oversized) transplant holes wit habout half compost and half native soil. When I sow directly (peas, carrots, beans, herbs), however, I have a little less luck. Also, last fall I decided to plant garlic in a place that I hadn't planted it before...and those garlics are now developing some rotting issues that I think I can at least partially "blame" on the soil. I'd like to amend so I can rotate plantings as much as possible.

So, what do folks suggest? How should I go about amending my soil to get that nice loose stuff that I see in so many how-to videos and the like, without building raised beds? And is it even possible to do so?

imafan26
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Just keep adding compost and mixing it into the soil. I also have heavy clay but it is not hard. My vegetable garden has been amended for years with leftover potting soil from the pots, compost, and now I add some vermicast from worms.

Over time the soil will improve.

If you have an area cordoned off, try lasagna or sheet mulching building up the beds. It is a permaculture technique where you don't necessarily dig down, but build up instead. You do not need to build a planter box as you can just hill the sides up instead. This way you will be planting in well aerated and well drained compost. No till also disturbs the soil web the least, over time the mulch will decompose, but you will just keep adding compost every year. It also helps to plan your vegetable bed so you minimize walking on it that way it won't compact as much.


https://www.plantingjustice.org/resource ... etmulching

mattie g
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Thanks, imafan.

This spring, I added some compost and old potting soil to my vegetable sections, and was planning to continue doing so. I'm glad to hear someone back up that idea, so I guess this is a good option to move along what I'm trying to accomplish. I don't want to disturb things too much, but I'm not opposed to removing some of the heavier sub-soil and replacing it, if necessary. I'd simply be moving that soil to another part of the yard that could do with a little building up.

I'll look into the sheet mulching.

An interesting side note on the soil in my garden...The previous owners of our home built a playground area for their kids, which we turned into our current garden. The playground had been mulched with large wood chips, which had started to break down by the time we moved in. It also had a sandy area for a small sandbox that had plastic sheeting under it. Then there's an area at the back of the garden by the fence that is under the branches of some neighbors' trees. That section of the garden has deep, rich, black-as-night soil. It's really gorgeus stuff - I'm sure it's benfitted from the leaves that have fallen there over the years. In the little section where the sandbox used to be, there's a mixure of that black soil and sand that has probably produced better than any other area for me. That side of the garden is something I won't be messing with anytime soon...other than to add some compost and compost tea here and there!

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TheWaterbug
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I have heavy clay as well, and I think the other posters have it right--organic material, and lots of it.

I saw the banner ad for soildirect.com at the bottom of this forum, and I'm considering trying an order for later this fall, after my pumpkin harvest. I can get 10 cu yards of compost, delivered, for $458 in my area, which is $1.70/cu ft.

That's way less than what I've been paying for bagged soil (typically $2 - $3 per ft) and it includes delivery, which is worth a lot in time, trouble, and the absence of injuries to me.

The key questions are whether they'll deliver down the horse trail into my garden, as opposed to dumping in on the street, and the quality of the soil. They sell samples for $10, but I have no idea how large the samples are. I have an email in to them with some questions, so I'll update the forum if they come back with answers and/or if I get samples.

They also offer "forest blend mulch" and "amended topsoil (flower vegetable mix)" for $471 or $510 for 10 cu yards, but if the compost is good I'd rather have that.

Dillbert
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it is possible to "transform" a heavy clay soil into some super-stuff.

actually, given the higher mineral content of clay, it's more advantageous to start with clay than for example sand.

which is not to say it is a quick or easy "fix"- nor is started in pure sand, for that matter.
the traditional approach is add lots of organic matter and lots of sand, and double dig. the problem comes in at the interpretation of "lots"
if you're going to add sand, you need to add the whole hog. a loam soil is on the order of 70%+ sand, balance is clay and silt. those percentages are by dry weight. so if you heft a shovelful of clay - what, 15-20 pounds,,,, you need to add, and mix in well, 10-14 pounds of sand per shovelful.
the average garden has a lot of shovelfuls - it requires tons of sand - not a few bags from the big box store. I layered out 3 inches of sand, tilled that in, layered on another 3 inches of sand, tilled that in. repeat next year . . . . it will take 2-3 years to see a major difference.

you can also sprinkle on 5-10 pounds/1000 sq ft of gypsum to aid in 'chemically' breaking down the clay.

"double dig" - in order to get more amendments deeper into the soil, you amend the top layer, scoop it aside, then amend the 'not improved' layer below that. then pile everything back together.....

digging / tilling in organic matter is extremely helpful. again, it takes a lot of organic matter. stuff like grass clippings, fall leaves, mushroom soil, etc decompose rather rapidly into (essentially) dust. depending on what you can easily/economically get your hands on, finding "sufficient organic matter" can be challenging. I use my own grass clippings (and leaves) but I don't have a chem lawn service - I could easily get 4-7 times as many grass clippings, but I choose not to use the chemicized lawn residuals in my veggie plot. your mileage may vary....

your question struck me because earlier I was digging a hole for a transplant and the delineation of "good stuff" to clay was in-yo'-face clear. see the pix - not the same spot - this has about 4" of "good stuff" on top of (my yellow) clay. it has taken five seasons to get this far. this fall I'll scoop the good stuff onto a 'raised row', till in organic matter on the clay pathways, re-level it all. with a tiller, one can only get about 3" into the 'hardpan / clay" at a pass. after tilling the soil is all fluffed up - so that 3" of clay becomes 5-6" of fluffed up clay; then till 4-6 inches of organic matter into the fluffy 5-6 inches of clay, makes things better, but there is not "overnight perfect."
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mattie g
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Thanks for that, Dillbert. Very, VERY interesting! In addition to what I mentioned above, I was wondering if removing some clay and adding "other stuff" like sand and organic matter, then mixing back in, would work. I remember hearing that having clay as a base can be a good thing, so I'm starting off on a decent footing. And since my available vegetable gardening space is fairly limited, it shouldn't be terribly back-breaking or overwhelming to get the process going. I don't have a tiller, though...but with the small space it probably isn't really necessary.

I'll try to remember to take a picture and post what my soil looks like right now. It'll be cool to look back as I work on it.

Very interesting responses so far. I'm all ears for more!

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TheWaterbug
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mattie g wrote:And since my available vegetable gardening space is fairly limited, it shouldn't be terribly back-breaking or overwhelming to get the process going.
How much space do you have?

mattie g
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TheWaterbug wrote:
mattie g wrote:And since my available vegetable gardening space is fairly limited, it shouldn't be terribly back-breaking or overwhelming to get the process going.
How much space do you have?
I don't have exact measurements, but a guesstimate would put whole old playground at around 18'x18'.

HOWEVER...my total vegetable gardening space is about 1/3 of that. And I'd probably only try to amend about 2/3 of that 1/3 ( :P ), since, as I mentioned, the area near the back has soil of pretty high quality.

God...how I wish I had that whole old playground area to work with...

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TheWaterbug
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mattie g wrote:I don't have exact measurements, but a guesstimate would put whole old playground at around 18'x18'.

HOWEVER...my total vegetable gardening space is about 1/3 of that. And I'd probably only try to amend about 2/3 of that 1/3 ( :P ), since, as I mentioned, the area near the back has soil of pretty high quality.
So that works out to 72 sf, which sounds entirely manageable.

If you wanted a 4" layer to work into that, that's 24 cu ft, which will fit in a lot of cars.

I bought some bagged compost and some organic garden soil for $7.87/3 cu ft., which is $2.62/cu ft.

I haven't compared the two to see how different they are.

Here in Los Angeles we can also get free mulch, but you have to have some decent way to contain and transport it. Lots of cities offer this same type of stuff. Note that I refer to it as "compost" in that thread, but it's better described as mulch, because it's pretty coarse, but it should break down after a year or so.

Of course there are caveats about what's actually in municipal mulch, but you'd have the same concerns about most bagged product, unless you want to pay $10/bag for certified organic stuff or make your own.

mattie g
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Waterbug,

Yeah...I think I can get a good amount of material into my small SUV. There's a nursery around the corner from me where I get my bagged soils and composted materials. They also carry sand and all other kinds of gardening necessities, so I can get everything I need from there.

Since I do make my own compost (on a fairly small scale) and have a leaf shredder and plenty of lawn clippings, I'll have a good amount of home-grown organic material to work with.

I'm thinking I'll probably start doing some serious amending this fall. I'll plant my garlic in the sandy-ish area with the high-quality soil, so I won't have to worry about taking up a plot that needs some work done to it. The back (really good soil) part of the garden gets fantastic fall and winter sun, so I'll plant my fall crops there, and the rest of the garden will get the royal treatment. At that point, I'll start thinking about what to do for long-term amendments throughout the whole garden.

Edited to add: We have access to free mulch here in my county, but I haven't taken advantage of it yet. I'm just not completely comfortable with what might be in it. I should ask around to see if any of my neighbors utilize the service.

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One of my garden plots was clay and sandstone. Construction and landscaping of the house stripped off the upper soil layer and after forty some years of it being a weed fields the was still only two inches of topsoil over the clay/rock some of the clay veins were was blue gray just like modeling clay.


I mixed in about six inches of half composted hardwood chips (lots of nitrogen was added to quick compost it) and I planted a heavy cover crop of winter rye after the first season. That was five years ago I think. Now the soil is like coffee grounds with clay marbles mixed in and I can till it when it is fairly wet. I mulch heavily with fall leaves covered with grass clippings which helps a little but the wood chips realy changed the soil. I did it all without a tiller, but that really would have helped break up the clods.

Wood has calcium which interacts with acidic clay particles, and lignin which breaks down into humic substances which also coats clay particles and keeps them from sticking to each other. The wood and nitrogen feed soil fungus which exude various chemicals that also help the soil structure at a microscopic level.

For soil conditioning wood chips are ultra concentrated compared to compost from soft vegetation, and soft vegetation doesn't have the high concentration of lignin which is the hard part of wood. The down side is that it might take a year to adjust the nutrient balance.

imafan26
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Be careful adding sand, if the proportions are not good and the sub soil under the part that you dig does not drain well you will end up with cement.

I tried adding perlite, since it is lighter than sand. It worked for drainage but when combined with clay it forms hard chunks. Compost and organic material actually work better. However, by sheet mulching you will save yourself a lot of work because you really don't have to dig as long as the soil there does drain.

It was a playground before so the soil may have been more compacted there than the other areas of the yard so the soil may be harder there than in other spots.

18x 18 is a nice size garden. Mine is 8x16 ft about half of what you have, but I plant in more than one spot in my yard and I have more than one garden to take care of. I keep most of the bigger plants in pots and use the garden for plants that can be grown closer together.

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jal_ut
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Be careful adding sand, if the proportions are not good and the sub soil under the part that you dig does not drain well you will end up with cement.
I keep hearing this, but will not believe it.

The three main ingredients in all soils are clay, silt and sand. If your soil is leaning more toward clay, it can certainly be helped by the addition of silt or sand. My soil is quite heavy with clay and silt. The thing I can tell you is never work that kind of soil if it is wet. If you do it will make bricks, or in other words it gets very cloddy and the clods do not break up quickly. It is working the soil when too wet that is the problem, not the addition of sand.

Add lots of organic matter and some sand and it will help.

mattie g
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imafan26 wrote:It was a playground before so the soil may have been more compacted there than the other areas of the yard so the soil may be harder there than in other spots.

18x 18 is a nice size garden. Mine is 8x16 ft about half of what you have, but I plant in more than one spot in my yard and I have more than one garden to take care of. I keep most of the bigger plants in pots and use the garden for plants that can be grown closer together.
That's a realy good point in regards to the soil compaction, imafan. Very, very good point, and it would help explain why the "back section" near the fence has much more porous soil.

If only I could garden all of that 18x18 (or whatever the real dimensions are). In reality, I can only garden in about 75-100 sq ft of that, as my wife and I designed and set out some landscaping that takes up the rest of the whole old playground. To be fair, though, we planned that out before I really got the itch to garden like I do now!

mattie g
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jal_ut wrote:I keep hearing this, but will not believe it.

The three main ingredients in all soils are clay, silt and sand. If your soil is leaning more toward clay, it can certainly be helped by the addition of silt or sand. My soil is quite heavy with clay and silt. The thing I can tell you is never work that kind of soil if it is wet. If you do it will make bricks, or in other words it gets very cloddy and the clods do not break up quickly. It is working the soil when too wet that is the problem, not the addition of sand.

Add lots of organic matter and some sand and it will help.
I figured that out the hard way last fall, and ended up with some really big unbreakable clods sitting on top of my soil as it dried out. I took a hammer to a bunch of it to break it up, and eventually rains helped to break the rest of it down over time. I vow not to do that again.

While I'm curious about what imafan said about adding sand, my experience in this garden is that the sandy area I mentioned in one of my posts tells me that the sand isn't a bad thing for this soil.

I'm thinking I'll go with digging/tilling in organic material along with some sand, then I'll layer some leaves and grass clippings on top to overwinter. Hopefully by next spring things will have loosened up fairly well.

mattie g
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TZ -OH6 wrote:One of my garden plots was clay and sandstone. Construction and landscaping of the house stripped off the upper soil layer and after forty some years of it being a weed fields the was still only two inches of topsoil over the clay/rock some of the clay veins were was blue gray just like modeling clay.

I mixed in about six inches of half composted hardwood chips (lots of nitrogen was added to quick compost it) and I planted a heavy cover crop of winter rye after the first season. That was five years ago I think. Now the soil is like coffee grounds with clay marbles mixed in and I can till it when it is fairly wet. I mulch heavily with fall leaves covered with grass clippings which helps a little but the wood chips realy changed the soil. I did it all without a tiller, but that really would have helped break up the clods.

Wood has calcium which interacts with acidic clay particles, and lignin which breaks down into humic substances which also coats clay particles and keeps them from sticking to each other. The wood and nitrogen feed soil fungus which exude various chemicals that also help the soil structure at a microscopic level.

For soil conditioning wood chips are ultra concentrated compared to compost from soft vegetation, and soft vegetation doesn't have the high concentration of lignin which is the hard part of wood. The down side is that it might take a year to adjust the nutrient balance.
I've been using hardwood mulch the last couple years, then digging it into the ground in the fall. Perhaps I was doing something positive to start the amendment process without even knowing it...

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TheWaterbug
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TheWaterbug wrote:I saw the banner ad for soildirect.com at the bottom of this forum, and I'm considering trying an order for later this fall, after my pumpkin harvest. I can get 10 cu yards of compost, delivered, for $458 in my area, which is $1.70/cu ft.

That's way less than what I've been paying for bagged soil (typically $2 - $3 per ft) and it includes delivery, which is worth a lot in time, trouble, and the absence of injuries to me.

The key questions are whether they'll deliver down the horse trail into my garden, as opposed to dumping in on the street, and the quality of the soil. They sell samples for $10, but I have no idea how large the samples are. I have an email in to them with some questions, so I'll update the forum if they come back with answers and/or if I get samples.

They also offer "forest blend mulch" and "amended topsoil (flower vegetable mix)" for $471 or $510 for 10 cu yards, but if the compost is good I'd rather have that.
So I'm taking one for the team :D

Soildirect (finally) answered my email, and samples are shipped by USPS in an Ziploc freezer bag in a USPS flat-rate box. $10 is a lot of money for less than a shovelful of dirt!!! Well, I suppose they have to pay a buck or two for postage.

Anyway, I'm curious, so I bought one sample each of the 3 varieties listed above, and I'll report back with findings when I get them.

On a related note, I broke open those 2 bages of 3 cu ft. Kellogg's Organic Garden Soil for Flowers and Vegetables and the "N'Rich Compost" to compare. They look absolutely identical. The usage directions on the bag are identical. I wouldn't be at all surprised if they are actually the same product in two different bags, just to get more shelf space.

The texture is also very, very similar to that of the free municipal stuff. If I'm feeling up to it I may get a few bags of the free stuff on Friday afternoon and takes pictures of the three, side by side by side.



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