Heyo,

My question is how to amend clay or clay heavy soil. I've had a garden for 3 years in the north Houston TX area with mediocre results. I've got about 2-3 inches of top soil and then a thick layer of heavy soil that goes down several feet. I want to know how to build top soil out of the clay. Will heavy mulching do this? Any info would be appreciated. Thanks.

Del

Do you have a back-hoe?

Do you see white spots on the soil? Do you know the pH?

Definitely heavy mulching with have excellent results. I'd also recommend growing as much green manure as you can, especially plants with deep roots. Comfrey has been an excellent soil builder for us.

It's a small suburban lot,... I couldn't do a back-hoe though maybe some smaller equivalent. I don't see white spots in the soil and the is somewhat acidic but not greatly acidic. My pH meter show slight acidity. What top soil is there, is healthy and supports a good cover of vetch and clover.

I was speaking tongue-in-cheek. When it is dry, the clay here is either rock-hard, and you need a jack-hammer to penetrate it or when it is saturated, it is like thick, heavy gumbo, and a back-hoe is necessary to dig it up. We don't amend ours here in NE Mississippi, we just dig it up and move it to a landfill.

Hi Del,

You can amend each planting hole with a mix of native soil and compost for now and slowly work toward composting/mulching other areas as materials are available. Raised beds comprised of a mix of native soil and compost etc., or hugelkulture swales are alternatives as well.

Lol,.. I completely missed the humor in your comment! But your right, the clay is a mess when wet and when dry. Thanks for the info. Chelle, I've been doing exactly what you said in mixing native soil with mulch in pockets. It's a slow process.

It is a slow process to break clay down so that you can mix organic material into it.
I have used gypsum which is sometimes marketed as "clay breaker".
I put it on and after about a year---the clay is somewhat softened to about an inch.
I kept repeating this while adding organics---takes a long time to make good soil from clay!

CarolineScott said:...---takes a long time to make good soil from clay!

It does, but in the meantime you can easily garden above it.

Del, are you mixing wood mulch in the planting holes or compost?

I'm mixing in standard miracle grow "gardening soil". No wood chip mulch.

I had the grand idea that IF I could use a commercial tiller, I could break the clay up. Wrong. The tiller almost killed me (figuratively) and did not budge the clay. That's when I decided it was far easier to go up rather than down. I now have a nice raised garden in that area.

Del said:I'm mixing in standard miracle grow "gardening soil". No wood chip mulch.

Compost would probably be better than potting soil, and far cheaper, but I'm glad to hear that you're not doing what I did; when I first started out gardening in gluey-slime/brick-hard clay I killed innumerable plants by mixing wood chips in the planting hole.

What clay needs most is huge amounts of compost, like 50-50 clay and compost, mixed well.

You also have to KEEP feeding several more inches of compost every year to keep it from reverting back to clay. As the compost decomposes, the soil will subside and be tempted to go back to being soupy, pudding-like clay.

But who can afford an 8" layer of compost over their entire garden?
Plus another 2-4" every year?

My theory is that clay-plus-not-ENOUGH-compost can be greatly imp[roved by a little grit, coarse sand, bark chips, and fiber. They help the heavy soil stay "lofted" after some tilling every year or two.

I like to add coarse grit and fibers as well as compost, to help give some "structure" and help roots and worms prevent the clay from reverting. Grit can be crushed stone or very coarse sand , or coarse Perlite if you're rich. For "grit and fibers", I like shredded bark, for example ground-up bark mulch or nuggets. Coir would probably also be good.

Many people give clay-plus-sand thumbs-down. They say it makes concrete. Well, that's true! The problem is that clay needs COMPOST and lots of it. Without that, clay is hopeless. But if you can mix in SOME compost, ALSO adding some sand, fibers and grit help to keep the clay-and-compost from becoming pudding again.

I have another theory that fine roots growing deeply into this partly-amended clay help a lot in maintaining an open structure. Maybe, once you get enough openness and air into your clay, fungi grow mycelia which might also help to stabilize the clay and prevent it from slumping and filling all the tiny air channels.

I don't think that soft, gooey, flowing clay soil is suitable for no-till practices. You have to amend that clay and develop enough soil life and root penetration to support the clay and keep it open and aerated for "no-till" to work. (My opinion, anyway.)

While I am improving a bed over the first 2-4 years, I "fluff it up" once or twice the first year, once the second year, then again in a year or two more, depending on how many bags of compost I bought and spread over those years. Kind of like a very deep and through broad-forking, but usually with some mixing to get another inch or so of compost down into the root zone.

After "fluffing it up" like a souffle, to get as much open space and air as I can into the soil, I firm the surface back down to try to reduce the amount of slumping and "elluviation" that replaces the deeper air channels with anaerobic clay.

All that is just my quirky way of dealing with clay. I don't think it is widely believed to be effective. In fact, "sand-plus-clay" is heresy to many. Frequent deep tilling is considered barbaric by many, and destructive to soil structure by most. I just thnik that they are desperate measures designed to mitigate the effect of only buying 1/2 or 1/3 as much compost as the clay really needs, to turn into soil rapidly.

(Deep-rooted cover crops are probably the long-term inexpensive solution, if the roots go deep and leave lots of organic matter down there.)

Shredded bark fibers and small bark nuggets of all sizes below 0.2 inches would be better than wood chips or sawdust, for mixing into clay. Bark lasts longer, doesn't encourage nasty fungi, and doesn't cause as much nitrogen deficit (if any). I like pine, fir or hemlock bark!

"Heat-treated bark" sounds good to me, I just haven't ever seen it at the cheap places I shop.

Wood chips are great as top-dressing mulch. It will still break down over several years and release humus and soluble humus breakdown products to contribute organic matter to the bed.

I agree about raising a layer of amended soil ABOVE the clay. That way, you can garden successfully the first year, if you can afford enough soil. Water and soluble organics will leach down out of the raised bed, into the deeper clay layers, and soften the clay and attract worms. Over years, the root zone will grow deeper and deeper.

My subsoil is sub-clay, and SO impervious that I can't dig planting holes and amend them. If I do, they fill with water and make pure, anaerobic clay mud slurry. They take 2-3 days to drain, which means the roots have been drowned for almost that long.

I have to dig drainage trenches (slit trenches) to allow the "floor" of any below-grade hole to drain down to some lower spot in my yard, if I wnat to grow anything other than anaerobic batceria in those holes.

But if your subsoil drains ("perks") in an hour or so, you can probably do it in your yard.

Yep, you could do all that,
or just slap a raised bed on top and get to gardening.

That's what I'm talking about!

Some county landfills make compost and either sell it cheaply by the truckload, or give it away (but you have to load and transport it yourself). I'd check with your County Extension first, for the best source of a large amount of compost. Here they make fabulous compost and give it away for the taking. In Salt Lake City, where we made a garden out of a baked clay moonscape at my daughter's using 30 pickup loads of compost, it was $25 to fill the pickup - two scoops of their front-end loader.

The big thing about adding any natural amendment (anything that was ever a plant) is that it's made of cellulose fibers. Those fibers act like tiny sponges once incorporated into your soil, expanding when they get wet and contracting (to leave little air pockets) when they dry. What clay soil lacks is those air pockets. It's made of particles so fine they settle together and don't leave any gaps.

Compost is the best, because it's already partially broken down, so it's not stealing nutrients from the soil around it to decompose. Mulch decomposes faster if it's on the surface, and the fibers filter down into the soil eventually to add those fabulous fibers to the mix. You should always use lots of mulch, to keep your clay from baking into a giant brick whenever it's sunny.

Green manure, of the right type (usually a nitrogen fixing legume) tilled in adds lots of fiber but takes a little while to break down. I'd be tempted to do that in the summer and let it 'rest' while the heat and rain do the decomp job. From what I've been hearing of Texas summers lately, you don't want to do too much gardening in summer anyway.

I appreciate all the info. It's interesting to hear the different approaches. After 3 years of various methods (raised rows, raised pockets, tilling(which nearly killed me also)) my produce isn't really improving. My suspicion is the clay and acid levels. With the very thin layer of top soil I have, I can make cowpeas and okra but everything else is generally of poor quality. It could be my poor gardening techniques but it's more fun blame the wretched clay. Thank you all for your advice.

I found this forum and site by listening to a permaculture podcast (Permaculture voices) that had Dave on as a guest. It's quite a good little community you all have here. Thanks agian.

I am faced with the same problem with clay in Huntsville. When my father in law built the house in 1973 (next to a lake), the lot was a swampy area and he had 150+ truckloads of clay hauled in. When we moved in to the house 7 years ago, i found two to three inches at best of topsoil. As I have worked on building up the soil, I have brought in several truck loads of mushroom compost from Madisonville, mulch from several other sources and started a hugel swell. When I have to dig down into the clay I will also add expanded shale to attempt to loosen it up some, in addition to mulch. It is a constant work in progress. I have eliminated 50% of my turf grass area and am mulching and building raised beds. I have been in the process of converting to an edible landscape design after hearing Dave the first time two years ago at Arborgate.

My advice like the others in to heavily mulch with good organic materials. It won't happen overnight, but it should continue to improve with time and effort.

We live in Kingwood (9a) and have treated our soil with Lime for several years. It is like baby powder and went on very easily. There was one area that was particularly bad. We tilled in lime and compost. It's still the hardest area in the yard but manages to grow Dwarf Monkey Grass instead of lawn. We continue to add compost and Mulch every year. It works it's way into the soil eventually and we've noticed the difference. The youngest raised bed we have is 8 years old. The soil there is getting better and better.