Improving clay soil on the cheap

I am curious whether anyone here at Permies has had good success improving heavy clay soil with spending a lot of $$$ on it.

It's generally understood that to improve clay, you have to add a lot of organic material. But it's a challenge to produce enough compost to keep my small raised-bed garden of good soil, much less the massive quantity needed to convert a large area of clay.

I have experimented with blending in dry brown leaves a year ago, but haven't seen any difference in that area. I don't think the leaves break down quickly enough.

I added some partially-rotten wood to a small area of clay to see if it could form a mini-hugelkultur, but it hasn't had any impact. It may take much longer, so not very practical for me.

If you wanted to turn a fairly large backyard area of heavy clay into productive soil as quickly as possible with minimal investment, what approach would you take?

Without knowing your goals, I would pile a foot or more of wood chips on every area possible.  Depending on what you want to grow, I have heavy clay soil and most things grow just fine in it.  An annual garden is a different story.  The best thing for that, again, is wood chips.  When you want to plant it, you can pull back the wood chips, put some good soil or compost in the trench or hole or whatever, and plant directly in that.  It will take some time, but will create really beautiful soil.

The best way to start new gardening space and soil amendment is required is horse manure. If you google horse boarding and your town in the search something always comes up, even for NY City. And it's always free.

Look at the product before you go ready to haul some. Only take aged/composted manure. Never get horse manure with wood chips or shavings in it. And test it to make sure a mixture of say 4 parts your soil and one part the manure will germinate seeds. If there's wood in it the seeds won't germinate and it may also have herbicides in it.

If you direct seed into your soil never add any wood chips to it as the seeds won't germinate.

The lawn I converted to a garden had a 1/2 inch of sod and nothing else in it. I dug in 3 inches of manure with a spade. It works best if you do two passes. My clay took another inch over the next 2 years and it now looks like fairly decent loam. I don't recommend planting root crops and leafy crops in freshly manured soil. But if if you do it now, it'll be ready next spring. So do the areas you might plant the root crops and leafy stuff first.

I have done what you are wanting to do. In fall I dug it all up about a foot down to break up the concrete-like clods and pick the rocks and chunks of pure white clay out. Then I mixed in a lot of caca de caballo. I mounded it up and covered with wood chips, filling in the low parts with chips to make the beds only look 4 inches high or so. Following that I planted a "soil builder mix" (From Peaceful Valley Farm Supply, shout out) in the beds and turned all that under the next spring. It was pretty heavy still the first year but I grew some stuff. Toms, lettuce and squash grew fine in the clay. Cukes and peppers were ok. Good mulch and the perfect amount of watering goes a long way in my experience.  Since then, I have been adding a little compost and worm castings as I produce them and it seems to be working as God intended.

Total cost was like $10 for seeds and whatever the gas was to grab the free manure from a neighbor.

Or... You could spend $100 on 2 yards of compost and turn that in. I did this too in another spot and the results were about the same. The soil was looser, quicker but the growing result after the first year were pretty similar.

Also, a Fiskars digging fork is worth it's weight in gold in heavy clay.

Good luck! Don't dig wet clay!!!

I can tell you a lot of things that didn't work and something that seemed to help.  Heavy clay soil, virtually no organic starting.  Shale rock about 18 inches down.  Soil pH 8 to 8.5.  High sodium content.

Tilled tons of straw in, many truck loads of manure, added gypsum by the truck load, grew green manure and tilled in.  Many hundreds of pounds of soil sulfur, copper sulfate, ammonium nitrate added.  Did this for about 25 years.  Soil when we started freshly tilled soil that was basically waterproof.  Run a garden hose for 12 hours and it soaked about about 1/2 inch.  By the end in freshly tilled soil it would soak out a bit over a foot in 12 hours but still had poor adsorption.  Still beats to powder and the color was almost the same.  Shale rock is a bit over 2 feet down now as frost freeze thaw has made more soil(using the term loosely)   Soil pH is still high 7's.   Did all the "right" things.  Some improvement but not great.

In 2007 mom developed health problems and the only garden crop I got in that year was potatoes.  Grew them in clippings to make picking easy.  The second clipping burial I mowed the cheatgrass and a few other weeds and used those clippings to bury the potatoes about a foot and half to two feet deep in clippings.  ((Side note apparently I mowed at exactly the right time as I got no cheat grass from the clippings the next year plus it didn't regrow where mowed and by having cleaned the garden of it there was NO cheatgrass the next year.))  Mowed main lawn grass another time and increased burial depth later in the summer.  While harvesting the potatoes scattered the clippings over a path about a dozen feet wide.  Was too busy with moms health to grow a garden the next 4 years.  So I mowed the weeds and watered was all.  Any place the mower hit the clippings from off the potatoes I let it scatter them that much more.  Had a few patches of lawn grass creeping in from the sides.  Left it unmowed till the grass seeds were ripe and then mowed it such that I scattered the seeds but mowed all the weeds a number of times.  Repeat mowing pattern protecting grass till ripe and then mow to scatter seed but mowing everything else on a regular basis and keep watering.  By 2012 the lawn grass has basically taken over the entire garden.  It is far healthier than the lawn in spite of getting nothing but water and no mowing till seed ripe.  Weeds had basically disappeared.  But the real change was in the soil.  It was far darker, had cottage cheese texture(I didn't understand the value of this yet), had earth worms for the first time ever.  But the most noticeable change was I would easily break the damp shovel full up with my hands as the roots were all that was holding it together.  Back in 2007 that would have been mud that was almost unbreakable in the shovel full.  Other interesting thing is the soil pH now is testing 7.3-7.4  The plain and simple fact was I did more in 5 years of mostly benign neglect and weed control with the mower combined with stopping tillage than in 25 of working my butt off at it with much expense.

So in about 2013 or 2014 I got to the first modern soils sciences class.  Pushing no till, bio diversity of plants, carbon building etc.  Now I understood the value of the "popcorn" texture in the soil.

The old timers in this area always said to improve clay soil plant sugar beets.  I always thought it was an old wives tale till I got to those classes.  Now I understand those deep roots are the tillage tool to break up the soils.  And more importantly to provide a pathway for moisture to enter the soil.

Still need to play with biochar as an amendment.  Will it help.

So if I was starting in new heavy clay that grows basically nothing.  I would do all my tillage to mix in soil amendments, contouring & swales etc the first year and simply try and grow anything that will grow including weeds.  Year 2 I would finalize any soil contouring but would try to disturb as little soil as possible and throw the soil building cocktail of seeds at it with a heavy concentration on deep rooting stuff like sugar beets, daikon radishes, turnips etc.  Add a nitrogen fixers and grass seed etc.  Raised beds I would build hugelkulture into them knowing they are going to settle over time with the same soil builder cocktail.  Current thinking to try for soil amendments.  Straw just to help get it water penetration first year, wood chips for sure.  Try biochar in a few places.  Charge the wood chips and the biochar by tilling it in the manure pile ahead of time.

To me, "on the cheap" means anything I can get for free.

Some possible "free" organic matter would be veggie scraps, grass clipping, leaves, wood chips, and coffee grounds.

Look for people putting those out as trash.  Homeowners and restaurants.

Try Chip Drop for wood chips.

Also consider mushrooms growing for soil health.

I don't know what area you are in, but here in Texas, autumn leaf season is about to start. Farther north I'm sure it's already begun. Tons of free organic matter, neatly bagged up on every curb, free for the taking. It won't fix the problem immediately, but it will definitely help.

It seems to me with soil improvement, "fast" usually isn't cheap, and "cheap" isn't usually fast. Obviously, raised beds full of compost will allow you to plant  right away, while improving the soil underneath, but that won't be cheap. Lasagna or back to Eden type methods can be free or very cheap, but not super fast. But if you are in the Northern Hemisphere, and just heading into winter, you still might be able to get a good jump on a lasagna garden that would be ready to plant into in the spring, with minimal purchased inputs. It all just depends what is available for free where you are. I can get pretty much unlimited free pumpkins right now from local pumpkin patches.. I got a few truckloads for ourselves and our animals, but now am wondering if I should go get some more for composting, to go along with all the fall leaves I'll be collecting.  

One cool thing I read about recently, that I'm excited to try, is vermicomposting trenches. Basically dig a trench, layer in worm bedding and compostables, add some worms, layer on insulating straw, etc, on top, and let it sit. When it's all composted down, you can plant either directly in, or next to the trench. This the blog I read about it on; he explains it better than I. https://www.redwormcomposting.com/large-scale-vermicomposting/the-vermicomposting-trench/

And this is a truly awesomely inspiring thread by Bryant Redhawk on how he used straw bale gardening on top of clay to not only be getting crops the first year, but also improving the clay soil underneath while he did it. https://permies.com/t/108953/improve-clay-soils-growing-year.  Whether this is practical for you will depend if you can get herbicide-free straw cheaply where you are. Or there may be a variation that works for you where you are; great stuff to read no matter what; gets those mental wheels turning

Also, depending what your goals and resources are, you might want to just focus on improving one smallish area at a time. Doing a small area well and getting a yield will be much more satisfying and productive than spreading your resources too thinly over a large area, and not seeing good results.

Lila Stevens wrote:
It seems to me with soil improvement, "fast" usually isn't cheap, and "cheap" isn't usually fast.

Like most everything.  Fast, cheap, good.  You can have two of them.  

TIMEFRAME is important.
In permaculture, we usually look at our soil amending plan on the scale of years, not just a couple seasons.

Like Lila said: Fast usually isn't Cheap. Additionally 'Cheap' doesn't mean 'Low Effort'  - Doing something in a short amount of time isn't quite the same as doing it 'easily.'

You mentioned leaves & rotting logs. Both of those are high-carbon and decompose slowly. They help soil structure and water retention and make healthier soil in the long run and ARE important, but if you ONLY put carbon in an area, and not corresponding nitrogen to help break it down quickly, it'll be sooooo sloooowwwwww to decompose.
They need other good rottable stuff to go fast. Stuff that turns sludgy and nasty smelling when it rots. That's the green stuff you gotta mix with your browns, so your soil can feast as fast as it can.

It's about feeding the life in your soil - not feeding your plants. You feed the soil, the soil feeds your plants.

The soil life is what eats rocks and slurps up organic stuff and poops out nutritious plant food.
Feed the worms, the fungus, the beetles and protozoa. Feed the bacteria!
Your friends in the soil enjoy manure. They LOVE decay and fermentation. They feast on things like rotting meat and plants.

Make them a cozy home for them with a big pile of woodchips -  it's insulated from the cold and scorching heat, and holds the moisture in after it rains, so they don't shrivel up.

Cultivate your soil ecosystem - spoil them with rottable goods like you'd spoil your pets with treats!
Get a big barrel, fill it with water, and let green weeds FERMENT for weeks, then treat your soil to some tasty sips!
Rotting meat and spoiled leftovers? Bury it.
Found a dead animal? Bury it.
Stale dogfood? Bury it.
Rain-spoiled hay from a local farmer, coffee grounds from a local cafe

Your neighbors left out leaves and lawn trimmings? Swipe them, chop 'em up, and bury them. Or just pile them in a big heap where you want to garden. Turn the whole garden into your compost pile for a year.

Become someone who LOVES seeing rot and fungus and decay, because that means you found something you can feed to your yard!

Congrats you've adopted several trillion individual life forms. They're your pets now, and they have a nifty side-effect of making plants grow real good.

Feed your babies.

Hey that is a really important point. I didn't include it originally but I douse my clay with compost tea every year just to be sure I got what I need in there. Maybe that's why I can grow veggies in soil that I can't "stick my arm up to my elbow in". I am up to a finger now though which is better than when it was close to pickaxe-proof.

Toko Aakster wrote:TIMEFRAME is important.
In permaculture, we usually look at our soil amending plan on the scale of years, not just a couple seasons.

Like Lila said: Fast usually isn't Cheap. Additionally 'Cheap' doesn't mean 'Low Effort'  - Doing something in a short amount of time isn't quite the same as doing it 'easily.'

You mentioned leaves & rotting logs. Both of those are high-carbon and decompose slowly. They help soil structure and water retention and make healthier soil in the long run and ARE important, but if you ONLY put carbon in an area, and not corresponding nitrogen to help break it down quickly, it'll be sooooo sloooowwwwww to decompose.
They need other good rottable stuff to go fast. Stuff that turns sludgy and nasty smelling when it rots. That's the green stuff you gotta mix with your browns, so your soil can feast as fast as it can.

It's about feeding the life in your soil - not feeding your plants. You feed the soil, the soil feeds your plants.

The soil life is what eats rocks and slurps up organic stuff and poops out nutritious plant food.
Feed the worms, the fungus, the beetles and protozoa. Feed the bacteria!
Your friends in the soil enjoy manure. They LOVE decay and fermentation. They feast on things like rotting meat and plants.

Make them a cozy home for them with a big pile of woodchips -  it's insulated from the cold and scorching heat, and holds the moisture in after it rains, so they don't shrivel up.

Cultivate your soil ecosystem - spoil them with rottable goods like you'd spoil your pets with treats!
Get a big barrel, fill it with water, and let green weeds FERMENT for weeks, then treat your soil to some tasty sips!
Rotting meat and spoiled leftovers? Bury it.
Found a dead animal? Bury it.
Stale dogfood? Bury it.
Rain-spoiled hay from a local farmer, coffee grounds from a local cafe

Your neighbors left out leaves and lawn trimmings? Swipe them, chop 'em up, and bury them. Or just pile them in a big heap where you want to garden. Turn the whole garden into your compost pile for a year.

Become someone who LOVES seeing rot and fungus and decay, because that means you found something you can feed to your yard!

Congrats you've adopted several trillion individual life forms. They're your pets now, and they have a nifty side-effect of making plants grow real good.

Feed your babies.

Well said Get excited about all of this, and your soil will get better and better over time.

Dan Fish wrote:Hey that is a really important point. I didn't include it originally but I douse my clay with compost tea every year just to be sure I got what I need in there. Maybe that's why I can grow veggies in soil that I can't "stick my arm up to my elbow in". I am up to a finger now though which is better than when it was close to pickaxe-proof.

I'd say that is amazing progress. I have some areas of my land that are hard, hard clay. Getting it to where I could poke a finger in would be amazing. Luckily I have sandy portions too, and those are what I am currently improving and gardening in. Now I want to see what I can do for the clay parts, just for fun.  

This pile cost me 0 $.

Thank you for all the suggestions. I will keep thinking about this and experimenting in small areas.

To those who suggest getting "free" manure or other local products for "the price of gas", there seems to be an unspoken assumption that we own, or have access to, a pickup truck or small trailer. We don't. Buying fertility in quantity generally involves us paying for delivery.

We have a small, highly productive garden of raised beds, where we grow intensively in highly improved soil, an approach to Mel Bartels square foot gardening. But we could grow much more if we could utilize some of the native clay outside the small intensive garden.

We get 150+ bags of raked leaves just from our own land every year, and dump them in a large pile to decompose. The upper layers provide a source of leaf mulch, and the lower layers leaf mold. But it still produces relatively little leaf mold, enough to supplement our small, highly improved garden beds, but not enough to impact an area of hard clay.
The same goes for our kitchen scrap and grass cuttings compost pile. Excellent stuff to keep small beds productive, not enough to make over hard clay.

It takes an awful lot of added fertility to keep any garden productive, especially one where food is grown intensively or on clay.

We're in Vermont, so heading into winter and won't be doing any more soil work until spring.

Best wishes to everyone who made suggestions.

Yeah If you can't get material you are well and truly hosed with trying to improve bad soil. There is no magic pill or technique that I am aware of, especially for free. It's all in the bulk.

Hey Lila, thanks for the encouragement. Also, I bet the clay will make better garden soil once you get it "adjusted". Lots of minerals and water capacity after you do a few million hours of heavy labor hahaha.

Yes, the problem is the need for bulk. Initially I thought it was just a matter of adding copious leaves and partially rotting wood to a small area, and waiting a year or two. But the small area I treated doesn't seem to have improved.

Looking at descriptions of top quality loam soil, the optimum balance seems to be large quantities of organic matter, fair amount of sand, and a small amount of clay. So starting with the clay is sort of upside down.

I was hoping to find a way to improve clay with small amounts of quality additives, but if it's about quantity rather than quantity, I'm just not in a good place to do that.

Lots of good suggestions above, adding leaves, organic matter and the like. Things that have worked for me is to stop tilling. I'm not sure exactly why that worked but the difference was rapid and pronounced. Also, someone mentioned beets. I haven't used beets, but turnips and daikon radishes planted late summer and left to rot the next spring help a lot. Also very helpful but maybe a bit distasteful in some circles are deep rooted weeds like thistles, dandelions, burdock and mullein, let them grow up big, then chop and drop.  All very cheap and very effective but it does take time.

It sounds like you want good quality soil as soon as possible with little cost. I have 10x area bigger than my garden with very poor clay soil to improve, I wish I could do that too! But like the old saying " good, fast and cheap, choose two" we have to trade depending on what the priority is.

As in the raised bed garden, you get quality in less time by putting lots of resources. When it comes to the bigger backyard, you will have to bring in large quantity of organic matters from outside, being wood chips, manure or compost like others suggested.  No double that's costly and labor intensive.

I am wondering if you could take a slower step and make use of the land while you source organic matters to build up fertility. Here are several things I am doing in my yard that maybe related to your situation.

1. Grow the plants that will survive in poor soil for food or biomass. In my case they are sunchoke, sorghum, sweet potato, goji berry and mulberry.
2. Encourage native plants and wildflowers to provide habitats for beneficial insects. They help a lot with pest management in the main garden.
3. Use the area for squashes and pumpkins to sprawl. Since the leaves kept the soil underneath moist I saw clovers slowly replacing grass and add fertility to the soil.
4. Sow a mixture of ground covers so there are roots growing in the soil and feeding soil microbes year round.

Clay soil is very productive once you get the organic matters in and the healthy soil food web going. It takes time and efforts but it's totally rewarding.

About the lack of a truck to get manure. By the way it costs me $42 to rent a pickup to get to and from my barn for manure. That price is before the prices of everything went crazy.

This year I decided to get some fresh manure to add to my leaf pile to test how that would speed up the composting from something less than a year and a half. I got 5 bags of manure in heavy contractor plastic bags and hauled them on top of the car. The last time I did that was the spring of 2021 for my hot frame and that time I got 9 bags. I worked with a guy who told a garden story of his dad. Every spring his dad went and got manure which he shoveled into the trunk. His story finished with: "I knew when the smell started to dissipate that it was time for the next load".

There's also the possibility of borrowing a pickup or a car and trailer. Change your shoes before you get into someone else's vehicle after loading.

Any organic matter you dig into clay will improve the soil. I've dug in a limited amount of uncomposted leafs. Even the big thick oak leafs off the Pin Oaks which come down in spring can be dug into clay. I checked a map and decided you're too far to go to the coast to get sea weed. So what about 4 or 5 gallon buckets of coffee grounds from Starbucks stores. I've never done it but some say they "Will" give you used coffee grounds if you ask. One more thing. Your kitchen scraps; my mother always dug it into the ground all winter. She stacked bags, the ones they give at the produce dept, with the kitchen scraps. They froze and when the ground thawed enough to dig them in; she did. You're probably going to have longer frozen ground periods; but by spring most of what you dug in will have disappeared into the soil. In the summer you can either dig them into rows or into new ground under development. Or compost it with pulled weeds and grass clippings.

Dan Fish wrote:Hey Lila, thanks for the encouragement. Also, I bet the clay will make better garden soil once you get it "adjusted". Lots of minerals and water capacity after you do a few million hours of heavy labor hahaha.

That's a very good point. I'm locating my new compost heaps right on top of some clay this fall, because it is convenient to my goat and chicken pens, so it will be fun to see how and when the actual soil beneath starts improving. If the soil gets nice eventually, I could use it as a planting area.

May,

I am trying to get sunchokes started out there. It remains to be seen if they can survive the voles. :-)

The area in question doesn't even grow good grass, so it's probably nutrient-poor as well as dense and heavy soil.

Straw and livestock manure. I farm on heavy, clay muck. If you farm, Cathy, you need a truck, even if it's a small farm truck. I drive a small beater farm truck for hauling small loads and small livestock. If it gets punched by a cow, I don't cry.

Would it make sense to buy a bunch of sand and fork it into the clay?  I seem to recall sand is cheap.  In theory, it seems like that may move your soil closer to balance, and if you do that along with organic matter, it may help your sand turn into good solid loam.

Cathy,

I have heavy clay as well and I had to amend it to get decently workable ground.

My solution was not so terribly expensive but did require some work.  I trimmed a LOT of weed bushes and ran them through a chipper.  Those chips I then inoculated with mushroom spawn, specifically Wine Caps.  The mushroom compost did absolute wonders for the clay beneath.

The mushroom part of the process is not so terribly difficult and if you like, I can give you a few pointers.

Eric

Don't add sand, it just makes things worse. You're starting to make the recipe for concrete. Organic matter is the key. Trust me, I have buried my tractor 6 feet down in cold muck and dug it out by hand. Learn to work with the clay.

The lack of truck definitely makes things harder. I don't have a lot of "normal" things, but I do love my little pick-up truck!

If there is a mushroom farm or other source of free compost nearby, there may be someone with a dump-truck making their living by delivering the goods to gardeners and farmers. It may be less expensive than you think. It would depend on distance.

Since your intensive beds are working well for you, you might just consider extending those out gradually, resources permitting. If your clay won't grow grass well, it probably won't grow cover crops well enough to help. But if you can improve it enough to grow cover crops, that would gradually help it get ready eventually to grow veggies. But yeah, it'll either take time or money.

On a positive note, at least you have soil! I used to live on the Big Island of Hawaii. The part I lived in had literally an inch at best of "soil" (actually mainly broken down plant matter) on top of asphalt-like lava. So there was no "improving" the soil; there was just building up on top of it, mainly with soil and compost purchased elsewhere, if you wanted to have enough to plant much food. So I'm now very grateful for both my sand and my clay here in Texas.

M Smythe,

We are not farmers, market gardeners, or homesteaders.

We live in a small town with a fairly large yard, and I try to grow as much our food here as I can. It has more in common with suburban gardening than farming or rural homesteading.

Hi Cathy, I started as a gardener, now am a farmer. A lot of things work the same from big to small. ❤️ If you can, try to source or produce organic matter to make that dirt living soil. Next year I'm putting in a fruit orchard, so like you, I gotta coax this clay into compliance.

The Most Important Thing About Clay:  do not expose it to the sun.

So organic mulch, mulch, mulch, 5"-6" maintained at that depth.  You can grow it yourself, and mow it when it's shin height....chopping it off and dropping it in place.  Wood chips, leaves in the fall from neighborhoods.

These things bring in worms that will "till" your clay soil for you.

I just can't say enough about how good clay soil is for nutrition in our plants (with minerals) and ability to hold water for the plants.

There are seed mixes for improving soil; oats, field peas, alfalfa...collect your local vetch seeds (they fix nitrogen), and native plants that will act as ground covers.    Mow these when mature, saving some for collecting seeds for next year.

Burr clover is not good if you have dogs and cats out in your garden, the burrs cause them problems in their ears and noses.   Otherwise, burr clover is great.  I have some that shows up voluntarily.  I don't let dogs or cats into the garden because the birds are doing a fantastic job on getting the bugs.

Tilling creates a hard pan layer at the depth of the blade of the tiller, pounding it into solidity, down where you can't see that it's happening.  You don't need to till if you mulch and bring in worms.

Bring in nature by feeding it with a deep, rich mixture of organic matter.  That feeds the soil, which will feed your plants

Yes, it will be difficult to improve a large area of clay soil quickly, without having truck loads of organic matter being brought in.
Last year we took 4 acres of depleted and compacted clay soil farm land out of the all too typical corn, soybean, winter cover crop, corporate rotation plan, and started converting it back into a more natural permie food forest. One free source of organic matter I have not seen mentioned yet is the left over, or used mash from small local breweries and distilleries. One of our local micro-brewers produces about 500 gallons of wet used rye, barley & corn grains per week, that they are quite happy that I come haul away for them.  I tried composting this spent grain all by itself in piles, or in my compost bins made from pallets stood upon their ends to make a container, but that did not work. The spent grain that did not ooze between the pallet slats decomposed slowly because it was not mixed well with other types of decomposing material. I also tried just spreading an inch or two thick layer upon the ground, but it still decomposed slowly and did not appear to be attractive as food for the birds, deer, or other local fauna. I did find though that when I tilled the spent grain into the clay soil it broke down very quickly. The small size of the individual grains that were already inoculated with a variety of yeasts, were pretty much decomposed within two weeks during the summer months, and about three weeks in the winter. After tilling the grain in about 3 times over last winter, the beds were soft and fluffy and produced good garden crops this past summer, and seem to be set now for future no till plantings.

If I had access to spent grains, I'd use it to feed pigs and let them rototill the clay before planting. They manure and turn the dirt over real good. Make sure tight fencing and don't let them into your pasture. They can do a lot of damage fast. I have pigs so I seen how quick they work.

The quickest way to start to improve any soil is mow the weeds and leave the mowings right where they were cut off.  Don't use a bag on the mower.  I let the weeds grow until just before they form seeds, then mow them.  That starts a thin layer of organic matter that then can be added to with wood chips (as opposed to bark chips.)  

Have you looked into the Back to Eden style of gardening?  Very helpful as far as bringing back fungi to the soil.

I add granite sand to my clay and it's done a great job for the last 30 years.  Granite sand is a 10-year source of potassium as well.  The only kind of sand that shouldn't be used is sand from an ocean beach because it has salt on it.

I wouldn't say it's crucial to add it, unless you are trying to plant something that just doesn't want to be in clay.  I avoid all of those types of plants   because they just get too fussy.  But plants that do well in clay take off as long as there's compost and thick mulch.

The only thing that makes clay worse is when it dries out.  Doesn't matter if it has sand or organic matter in it, if it's dry it's hard as a rock.  But the easy fix is get it wet again, and thickly mulch it, keep the sun off of it.  As soon as it's damp the worms will come up and happily work their way through it.

I'm wondering what the minimum amount of Organic Matter mixed into the soil will produce good crops in raw clay. OP has the problem of not having a truck or the money to pick up even free OM. Different crops are going to require more or less OM. Beans and peas will require less than tomatoes or peppers; and much less than corn.

Let's suppose we haul 9 bags, which I've done, of manure on top of the car. That'd be 12 cubic feet if the bags are a foot high, Spread out over a garden plot an inch thick would cover 144 square feet of garden or a plot 12 feet by 12 feet. The question is how well crops would grow in a plot with that little OM. I've grown Country Gentleman corn in an un-dug clay plot with no digging and no fertilizer at all. The crop grew very poorly, but that was a crop of corn which requires lots of fertilizers.

I'm guessing that a plot with an inch of manure dug in would grow an excellent  crop of beans and peas and nice crops of things like tomatoes lettuce, spinach, zucchini, cucumbers and winter squash . And also garlic. German Red garlic grows in the field next door where I planted the Country Gentleman corn. It grows small bulbs but we dug in an inch of manure to our new virtual plot. I wouldn't try to grow carrots or corn in this plot.

plant mino... radish they have very long roots to improve soil.

I haven't read all of this thread, but I did skim it.
Hopefully this  hadn't been suggested.
How about a pond?
A pond on the area of clay soil would take labor and or money but it could be an ongoing source of biomass for years to come.
Cattails and duckweed or azolla  wil make a lot of biomass.
Left to their own devices, they will actually fill in the pond itself.
A big shallow pond or a lot of small shallow ponds is what I might try.

If you haven't already, I'd also spend some time crawling the internet and learning more about your specific clay to see if there's something of use in there.  I watch market garden after market garden, townie after suburbanite battle to improve our clay soils without realising that our particular clay is an actual godsend.  It will hold water for forever as long as it doesn't dry out (read: isn't exposed to the sun and wind), and it holds nutrients for just as long.  I was just getting ready to double dig our clay when I learned about this.  Since then my tactic has changed and we've started building on top of it.  I brought in 10 trailer loads of sheep manure, and am 4 loads in to a pile of 30 loads of horse manure.  The sheep stuff was from a wool shed that hasn't been cleaned out in 30 years.  It's just magic.  The horse manure isn't as well rotted, but I'm tossing it directly onto a couple of our terraces with the worst of our soils and will plant a carbon cover crop to get us through summer before moving on to vegetables next spring.  Also we added several trailer loads of sheep's wool - the bottom fell out of the wool market here so we got it for the incredible price of the time to clean out a different wool shed - and wool is easy to compress and fit in a car.

That said, I realise that a pickup or trailer aren't available to you and that makes it difficult.  If you've got the money to spend, it's possibly worth seeing what the towing capacity of your car is and adding a trailer hitch so you can hire one occasionally.  When we moved to our acre all we had was a BMW 3 series hatchback.  I've hauled more in that thing than its rated for, including 1000kg of water, and I don't recommend that, but most cars do have towing capacity of some kind.  

Also, if you're in a small town that suggests to me you're likely surrounded by farms without needing to travel long distances.  Whatever it is that they're farming around you there will absolutely be byproduct that they're disposing of already.  If it's near enough, multiple trips in a car is totally possible.

Three other things:

In areas where I haven't added manure, I reckon the single thing that's helped my soils is that we don't own a mower and, at 2 years in, only just bought a scythe last week and only to make dropping buttercup flowers much easier.  Defo you can see soil fertility by what grasses have come up and how well they're doing.  Some of them aren't doing well but now that we've gotten through most of our spring boom I can say confidently that they're doing much better than last year.  The worst of these places are getting covered in horse manure in the next couple of weeks so I won't be able to compare next year.  We broadcast some daikon seeds shortly after we moved in and the first summer we had one pop up.  Last year we had three.  This year they're dotted all over the landscape.  We just let them go to seed and do their thing.  Also dock might be a great resource for you.  I brought in comfrey at first because I was supposed to, then I watched my land and watched the way that dock changes everything around it and what soils it grows on.  I'd never have worried about comfrey if I know then what I know now.  Sooner or later we'll start the chop and drop process, but that's probably another year from now.

I'd also use whatever community message boards, social media groups, or any other hyper local digital communication in a 30 mile radius and see if anyone has a trailer load of manure and/or downed trees or branches that they'd deliver for petrol + a 6 pack.  Or, as someone else mentioned above, there is bound to be someone who has a pick up or flatbed that's just trying to make a living and you could probably workout with farmers for them to load the manure with a tractor so it shouldn't take *too* long.

Also...humanure.  We're not there yet ourselves.  We're in a bus with a 400L blackwater tank and I find it a bit criminal, really, that once every 3 months I haul all those minerals off to a local dump station for RVs.  I'm still creeped out by the idea, but I'll also get used to it.
We're just not there yet, infrastructurally.  When we reno the bus after the rain stops we'll add a flush vermicomposting system.

And, as someone mentioned above, azolla or even duckweed.  Grow them in a bathtub, grow them inside, grow them wherever you can fit them.  That'll go a long way.

All of that said, when we bought the property two years ago, anything greater than a few mils of rain would run down our hill and drain onto the road.  Last year we only had two rain events where there was any run off from the terraces.  In this last week we've had about 10 inches of rain and our soils have soaked up every drop of it with no signs of run off except for down the drainage channels next to the wood chip drive.  Before next winter we'll bore out some soaker holes and stop that altogether.

PS - I did not intend to be so long-winded when I started this....

PPS - I just remembered another possibly viable option.  My sister in Austin has a neighbour with a community compost pile.  Those who choose to participate just bring their compostables directly to the compost pile in her backyard.  The owner doesn't even have to do the collecting work.