Breaking up soil compaction with plants

I've heard you can break up compacted soil using plants with deep tap roots and by building up soil life and organic matter. Has anyone had successful experience using these methods?

We have 12 acres of sandy, in parts stoney, soil. It is mostly in pasture (with quite a bit of plant diversity) with 1 acre being converted into food forest. Although the topsoil dries out too easily in short droughts, percolation tests show that water is slow to drain (1 hour on average). We are on limestone, which should be very fertile, yet fertility is low. I think this is because a hard, compacted layer is blocking nutrients from reaching the topsoil. I would greatly appreciate any opinions on this situtaion.

Siobhan Lavelle wrote:I've heard you can break up compacted soil using plants with deep tap roots and by building up soil life and organic matter. Has anyone had successful experience using these methods?

We have 12 acres of sandy, in parts stoney, soil. It is mostly in pasture (with quite a bit of plant diversity) with 1 acre being converted into food forest. Although the topsoil dries out too easily in short droughts, percolation tests show that water is slow to drain (1 hour on average). We are on limestone, which should be very fertile, yet fertility is low. I think this is because a hard, compacted layer is blocking nutrients from reaching the topsoil. I would greatly appreciate any opinions on this situtaion.

Yes, taproots will break up compaction. You want something that can grow through the compaction and then let it die and rot in place. Daikon is a popular choice. I had a temperate yam (Dioscorea spp.) that died in our summer drought and rotted in place, transforming a roughly 2 ft. deep section of heavy clay into beautiful soil.

I'm not sure what you mean about how limestone soil should be fertile. Lime is primarily used to alkalize overly acid soil as well as secondarily to add calcium (and sometimes a fair bit of magnesium, depending on the makeup of the specific stone.) Most limestone soils, from my reading, are overly alkaline, which means most plants are not able to uptake nutrients. From what I've heard, trying to adjust the pH of lime-based soils is one of the most difficult things you could try to do. I know that Steve Solomon's The Intelligent Gardener includes a section on amending lime soils, but I skimmed that section since it doesn't apply to my situation.

Here's a great overview of pH's effect on nutrient uptake:

I've heard from plenty of people that it worked for them, and it makes sense to me: some plants are extremely good at getting their roots down deep and they can do the same work that a tool would do.

That said, here in Georgia I have extremely dense clay soil under a thin layer of topsoil, and nothing I've tried (even daikon) is able to penetrate it. I figured that maybe I was doing it wrong, but David the Good posted a video of a friend of his in Georgia who was having the same issue. Sure enough, she had my recognizably dense, orange clay, and she showed how daikon would just kind of sit on top and wither rather than punching down. She ended up having to use a broadfork to break up just enough of the clay to get moving.

So I think the answer here is that there are a number of plants that can break up compacted soil, but you can definitely have levels of soil compaction that are beyond their capabilities. Someday I am going to try the method (which I think is Paul's) where you dig, like, six-foot holes at regular intervals throughout your space and fill them with organic matter. This allows the remaining, compacted soil to expand naturally into the gaps you've provided, while being enriched by the organic matter and the worms, etc. it attracts. The obstacle, of course, is that you have to dig a lot of really deep holes in really hard ground.

Matthew DeAngelis wrote:
That said, here in Georgia I have extremely dense clay soil under a thin layer of topsoil, and nothing I've tried (even daikon) is able to penetrate it. I figured that maybe I was doing it wrong, but David the Good posted a video of a friend of his in Georgia who was having the same issue. Sure enough, she had my recognizably dense, orange clay, and she showed how daikon would just kind of sit on top and wither rather than punching down. She ended up having to use a broadfork to break up just enough of the clay to get moving.

I like most of David's work but felt that video was kind of disingenuous. If you follow the research that's being done in soil microbiology, such as the work done by Elaine Ingham, then what we're finding out is that the structure is created by the biology in the soil. Heavy clays are heavy because they're very fine particles, and in dead soil there's no soil life (and their waste products) to hold those particles apart from one another. It's compounded by a mineral imbalance between calcium and magnesium (which is why you generally should not add magnesium to clay soils from sources such as dolomite and epsom salts.) Digging will always increase compaction long term... fine clay particles wash into the air spaces and are compacted by the weight of rain or irrigation, organic matter is quickly metabolized and escapes as gaseous elements, and the soil life that creates the structure is killed either in whole or in part.

Domesticated roots won't infiltrate to the depth that wild roots will be able to. Letting weeds grow is often the simplest solution. If nothing is growing there and you're not adding organic matter to feed microbes, and you're not adding the microbes themselves, then the daikons aren't going to get much of anywhere. You need more than one year if you're not importing anything. The first season of daikons needs to be chopped and dropped to feed the soil and over a few seasons they'll build up the organic matter and soil life. The idea isn't to grow daikons once and then give up; you grow daikons until you get them to the desired depth and then you plant your desired crop. There's a faster option, but that requires a certain level of training with a microscope. That is to brew an aerobic compost tea and then check it for the correct ratios of bacteria, fungi, protozoa, etc. and then apply that as a spray or drench on the offending soil. You still need organic matter for them to it, but this inoculates the soil with the right species in the right ratios to create a healthy soil environment which then creates the structure that allows for better air and water infiltration, plus all of the symbiotic relationships between plants and soil life.

I prefer the slow and steady approach because it's less finicky, but if you have a microscope and the skills and patience to put it to work, then that's certainly an option.

Here are some case studies that show the results of balancing the biology:



It doesn't go into the process, but there are lots of lectures to go into more depth about the science and process.

Wow, thanks Mathew! A lot to unpack here, but I'll certainly be giving daikon another try and I'll study the video in detail. I have mostly been layering (not digging in) organic matter in an attempt to build up a layer of topsoil, so I think I'm headed in the direction you suggest. I have a microscope, although not the requisite training, so taking a look can't hurt. But the slow and steady approach is more to my taste, so I'll keep at it.

I don't think that particular video was disingenuous, I think she was doing the best she could. It is hard, sometimes, to not feel frustrated when you cannot get your soil to cooperate.

Matthew DeAngelis wrote:Wow, thanks Mathew! A lot to unpack here, but I'll certainly be giving daikon another try and I'll study the video in detail. I have mostly been layering (not digging in) organic matter in an attempt to build up a layer of topsoil, so I think I'm headed in the direction you suggest. I have a microscope, although not the requisite training, so taking a look can't hurt. But the slow and steady approach is more to my taste, so I'll keep at it.

Hey Matthew! It's great that you already have the microscope and can start looking, and it certainly sounds like you're doing a lot of things right. Here's the first part of a class to help identify the different organisms in the soil under the microscope:

I don't think that particular video was disingenuous, I think she was doing the best she could. It is hard, sometimes, to not feel frustrated when you cannot get your soil to cooperate.

And I certainly don't think she was being disingenuous. David has a very particular strain of anti-science philosophy which, in general, I think is actually pretty justified... there definitely is a lot of corporate science that revolves around selling products regardless of whether it's based on good research. But then he'll post videos like this as an "example" of science not working when in reality he just didn't do his due diligence... or worse, he knows it's BS and is actively courting an anti-science viewership. I've definitely seen that in some of his more recent livestreams. In general I think his work is great, especially all of his work on composting and propagation, as well as his newer stuff on biochar/terra preta. I'm also glad to see him promoting Steve Solomon's work, as Steve wrote the bible on growing vegetables in my bioregion which I've been using for the past 15 years (though I don't understand David's need to rebrand Steve's work and make things more confusing than they need to be.) But Dave's been very resistant to the latest soil science and has done his share of work to discourage people from doing some things that would be beneficial to their soil... though he's not wrong about some of those things being difficult at his scale with his available resources. All in all I think his work is a net positive, but things like this make me cringe precisely because they end up getting repeated. But you can't have the good without the bad, so it is what it is. At the end of the day even his worst advice is still generally better than conventional agriculture, so I'm willing to look past the occasional video that misses the mark. If he's encouraging people to grow food, that's the most important thing. There are other people I've stopped following because they've repeatedly misrepresented the research just so they can claim that it doesn't work; David's the only one that creates enough good content to outweigh the bad.

I only watched bits of the videos because I have a metered internet connection so I'm sure I've probably missed something. I am also anything but anti-science but I don't apply it at all in my garden. At least not in an analytical way. I've never had a soil test for ph or anything else. I take the route that the soil itself in a real way is alive and I'm careful not to kill it but instead, feed it.  I suppose it is science to understand that microscopic things eat dead plant material and turn it into soil and nutrients for other plants but I don't have to know their names or understand their processes. A lot of things that I might see or read about would in all likelihood be beneficial but it doesn't matter because if it involves acquiring inputs not available on my property or following some specific instructions, I know I'm not going to do it. I don't have the money and time to waste on such things when all I want to do is grow a garden.

My soil is also a fairly heavy clay although at least in the older garden, not as heavy as it used to be. I use diakon or rather an adapted landrace of radish in general as well as turnips as winter cover crops, tillage and soil improvement, and have for several years. I don't "chop and drop" as that implies "picking up" first and I think that is a waste of time and energy.

The turnips and radishes are self seeding in my garden and pretty much always there in various stages of growth. During the growing season I just hoe off the tops of any that are in the way and or mulch over them. The turnips are winter hardy so in spring I hoe the tops off any offending plants and let the roots rot, the rest flower. I eat a lot of the seed pods and just let the rest scatter as they will.

The radishes are not winter hardy so I plant them in early spring and let many of them go to seed as well. Those that volunteer in late summer or early fall and not in the way of something else are left to grow on into winter. More are also planted at the same time or sooner. I've found that for the best soil improvement they need time to grow to some size before winter freeze kills them out so they are often planted right in the grow beds among and under other crops that are about to be harvested anyway. After the radishes freeze the corn stalks, bean or tomato vines or what ever else is just hoed off or pulled up and left to lay on top. In spring what ever is left is just raked into piles that act as mulch/compost between planting rows and it all starts over. The bare ground between is hoed into rows for planting, there is no "tilling" involved. That's all very general of course, sometimes as in the case yesterday I may rake a whole grow bed clean and plant carrots or something. In that case all the stuff raked up is just piled in a different grow bed and something else planted in it later.

Turnips and radishes are powerful tools for improving soil and have been about all I need but in the case the soil is too compacted for them to be effective and I know this may sound nutty but I would recommend dandelions and burdock. They both have very powerful roots. Dandelions are easy to control, they resent being hoed off level to the ground and they simpley can not tolerate even a light mulch. Burdock has the advantage of providing great amounts of green mulch which can be used against itself as  well as other weeds. My back garden is only about five years old and one whole corner of it had been a burdock patch for years. The soil in  that corner is black and fluffy, where the rest of it is the same typical clay as the rest of the place.  

As a disclaimer my whole gardening area is less than 1/2 acre so my practices may not be suited to larger operations. All of the work is done with a shovel, a couple different kinds of hoes and a couple different rakes. Labor is minimal, far less than years ago when I used powered tillers and kept everything neat and tidy. As a not insignificant bonus, production has increased by 100% or more as well over my old practices.

(Add) Siobhan Lavelle, I see you are in Ireland. I suspect you have dandelions but maybe not burdock but there are probably other weeds with powerful taproots you might utilize. Such things are often considered bad and can most certainly be so, but by watching their life cycle it isn't hard to learn how to control them and use their very tenacious qualities to your advantage. Also your talking about 12 acres, some of what I do might give you some ideas for a vegetable garden but don't know how it would work on such a large area. I only maintain along with the garden about two acres total, the rest of my land is mostly steep hilly woods where I plant grapes, berries and nut trees, I don't have livestock except the occasional chicken or turkey.

Mark Reed wrote:

(Add) Siobhan Lavelle, I see you are in Ireland. I suspect you have dandelions but maybe not burdock but there are probably other weeds with powerful taproots you might utilize. Such things are often considered bad and can most certainly be so, but by watching their life cycle it isn't hard to learn how to control them and use their very tenacious qualities to your advantage. Also your talking about 12 acres, some of what I do might give you some ideas for a vegetable garden but don't know how it would work on such a large area. I only maintain along with the garden about two acres total, the rest of my land is mostly steep hilly woods where I plant grapes, berries and nut trees, I don't have livestock except the occasional chicken or turkey.

Hi Mark,

Yes dandelions and burdock both grow here. There are already a good few dandelions, silverweed and other wild plants with deep tap roots growing in the pasture. It seems the land is working to heal itself. I will maybe try adding burdock, turnips and daikon radishes through mineral licks for the cows. I just checked and cows eat all of those plants, which will keep them under control. I guess the turnips and radishes, being annuals, will rot themselves but the burdock won't die for a long time. I wonder if there is a point in me adding burdock if I can't mulch it on the entire 12 acres. Will it have the remedial effect if it's left to live on?

I imagine burdock if left on it's own would eventually go a long way in improving the soils but I'd be hesitant to turn it loose on such a large area. It's easy to use and control in patches of a few hundred square feet but if it got well established, reclaiming several acres from it might be a bit difficult. I didn't know cows eat it so if that's the case it might stay in check. Otherwise assuming it colonized large areas when it came time to use the area for something else about the only way to control it might be to mow it down repeatedly.  

I wonder if cows really like it and if it is good for them or if it's just something they will eat if hungry enough. We have deer, which will munch turnip or radish to the ground but I've never know them to eat burdock.