Loosening subsoil

robbiemacAugust 13, 2011

I am prepping planting beds for next year. This particular bed is for flowers to attract pollinators and beneficials. It is 2' x 20' along one side of a raspberry row, and I will be doing an identical bed on the other side of the raspberry row. As a bit of history, nothing but weeds has been growing in this section of yard for many years. We've just kept it cut short and called it "lawn".

My original plan, and what I have done in other areas, is to till the top 6" or so and remove the loosened soil. The subsoil layer below that I loosen up with a digging fork to a depth of 6" and spread some compost on top of that. I then screen the rocks and debris out of the tilled "topsoil" and shovel it back on to the layer of compost. Then I begin adding in massive amounts of organic matter- grass clippings, autumn leaves, composted stable sweepings, and compost. By the following spring the bed is in better shape. Not great, but better. I then add more OM as I can, between plantings.

So I rototill this bed as deep as the tiller will go, which after I dig out the loosened soil is only about 5-6". Below this, the subsoil is as hard as concrete. Jumping on a digging fork, I can barely get the fork in about 4-5 more inches. And even that is a struggle. I tried a sledge hammer and a length of rebar, but that is very slow going as well. Any ideas on how to loosen up this layer of subsoil? This is the first time this area has been worked, and we have lived here over 25 yrs.

Thanks for any help you can give.

Rob Mac

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toffee-el(Z8b Sunset Z13 Elev 4650ft)

Jackhammer with Clay Spade.

My neighbors thought I was crazy for using an electric jackhammer to dig dirt. My back thanked me. It was late summer after 5-6 rain-less months, rototiller basically walked on the rock hard dirt. Jackhammer ruled, one of the best $60 per day tool in my experience.

    Bookmark   August 13, 2011 at 8:49PM
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Hadn't thought of that one. After I posted, I went back out with a pick and broke it up down to 5 inches or so. I then jumped on the digging fork and got it in, maybe a few more inches. I'll consider the jackhammer. Thanks.

    Bookmark   August 13, 2011 at 8:54PM
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toffee-el(Z8b Sunset Z13 Elev 4650ft)

Or you can wet the dirt.

    Bookmark   August 13, 2011 at 9:03PM
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val_s(z5 central IL)

I'm kind of wondering why you need to go so deep? If I'm reading you right, you're trying to go about 12" or more down. Yes?

If you're planting flowers, why are you worried about going so deep? For my gardens (veggies or flowers), I till about 6 to 8" then add my amendments and plant. I don't worry about what goes on below that. Nothing I grow goes that deep except for trees.

Just wondering.


    Bookmark   August 14, 2011 at 10:10AM
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dchall_san_antonio(8 San Antonio)

Plant alfalfa as a cover crop.

    Bookmark   August 14, 2011 at 10:31PM
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Activated Compost Tea will loosen sub soil. I didn't believe it either, but it does.
My plot had a layer of rock hard beneath a layer of good stuff, adding a soil drench of ACT made it much easier to get down there. But the no till brigade would suggest there is no need to 'till' it, provided there is sufficient drainage I agree.

    Bookmark   August 15, 2011 at 9:30AM
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toxcrusadr Clay Soil(Zone 6a - MO)

The pick or pick-mattock sounds like a good idea.

As for whether you need to, there is a long history in the literature of people double-digging and getting amazing results. Roots will penetrate below 6" if you give them a chance. It helps with drought resistance, and any kind of root crop - carrots, sweet potatoes, etc. - will benefit greatly.

You didn't say where you're located or what kind of soil you have, but I'm assuming clay?

    Bookmark   August 15, 2011 at 11:48AM
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toxcrusadr Clay Soil(Zone 6a - MO)

For anyone interested in why double digging makes a difference, there's a pretty good history of Biodynamic/French Intensive gardening here:


Task #1 in this system is double digging!

    Bookmark   August 15, 2011 at 5:54PM
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Thanks for all the responses. The lot that our house was built on was the last one built in this housing development. The builder used this lot to store all of the rock, sand, gravel, cement, block, heavy equipment, etc... So the "soil" before we moved in was all of that (except the equipment) mixed together and nicely compacted. Some areas are very sandy, some with a good bit of clay mixed in. We raised our 4 kids on it and all that entails (ballgames, digging bmx track, etc...). So now that the kids are grown, I am working on getting it productive. I am in southern NJ, zone 7A.

I used the pick for a bit- that worked but was tough going. The past 2 days we've had off-and-on soaking rain. When I went out this morning to do more work on it, it was still wet and loosened up with one jump on the fork.

My reason for going that deep was nicely put by toxcrusadr. I figure if I do this once, then keep adding organic matter each year, I should be ok.

    Bookmark   August 17, 2011 at 12:56PM
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You could do all that work and it is a lot of work and an article in Organic Gardening magazine compared the results of "double digging" versus just piling organic matter on the soil and found that after three years there was no difference. There will be an immediate difference, but long term none in reality.

    Bookmark   August 18, 2011 at 6:41AM
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There will always be a contingent declaiming "digging" or "tilling", convinced of their rightness.

Being the lazy sort, the idea of avoiding work has practical appeal.

Being a practical sort (and wanting to eat) I decided to try both methods and observe over the years.

Areas of double digging with the addition of organic matter are now over a foot of topsoil.

Areas of no-till that had organic matter piled on top have developed about an inch of topsoil. It is virgin soil below, in some cases anaerobic if I explore a few inches.

Both produce crops. The deep dug will grow anything, closely planted(provided sufficient rainfall or watering).
The no-till will grow shallow rooted plants with wide spacing, i.e., tomato,squash, melons, greens. It seems some plants send roots wide if they can't go deep.

Would your soil have the same results? Dunno.

Most of the people I personally know practicing no-till are using land their forefathers cleared with axe, plow and kids hauling off rocks.

Soil types and rock vary so much just within this county that I couldn't make a blanket statement outside of my driveway.

    Bookmark   August 18, 2011 at 7:49AM
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toxcrusadr Clay Soil(Zone 6a - MO)

You've hit the nail on the head alphonse, especially that last bit.

    Bookmark   August 18, 2011 at 10:23AM
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Good post!


    Bookmark   August 18, 2011 at 7:04PM
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toxcrusadr Clay Soil(Zone 6a - MO)

I'll tell ya a story about how much difference it makes to aerate clay. I dug clay topsoil (not very good topsoil) off the surface inside my new pole barn in order to fill a certain corner with gravel. About 20-25 wheelbarrow loads. I made a new flower bed by layering this about 2" deep (and some of it was big bad dry clods) with 4-6" layers of a mixture of leaves and grass clippings, plus about 5 gal. of last year's ash and cinders from the outdoor firepit. A lasagne bed.

Left it to cook over summer, it's still about a foot high. Unbeknownst to me, the wife planted vegetable seeds in the mound. Currently there is the largest zucchini plant I have ever seen, growing in this stuff. It gets some water but not as regular as the official vegetable garden.

Now I've been amending the clay soil in the garden for 20 years, and it doesn't grow anything like that. I have to think it's the aeration, room for roots to grow provided by the compost layers, and of course the fertilizer value of the decomposing compost.

I may dig up the darn garden and make lasagne beds next year since it works so well.

    Bookmark   August 19, 2011 at 12:05PM
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Just about every planting bed that I have made on this property I've done in this manner. One of the reasons for doing so is the amount of rock/stone that I have removed from the "topsoil" layer. I was able to dispose of one very large pile of stone, and another pile is now quickly forming- all from being screened out of the "topsoil". I see it as a necessity. Plus it is keeping me "young"!

Rob Mac

    Bookmark   August 19, 2011 at 10:24PM
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toxcrusadr Clay Soil(Zone 6a - MO)

robbie, you must be in one of those areas plagued by Swimming Rocks. You take them out and more rocks swim in there underground when you're not looking. Or the same ones if you didn't take them far enough away. :-]

    Bookmark   August 22, 2011 at 10:25AM
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Alphone, "They" tell me that Organic Garden magazine said:
You do not have to double dig or have 12-16 inches(30-41 cm) to grow vegetables.
This is to get Urban Knight to start to grow organic gardens.
I agree with you & have double dug for 30 something years.
You can grow vegetable on top of an A-frame house, but why would you, if you can double dig ONE TIME & add compost every Spring & Fall?
My OGM book says a pepper plant will grow 48 inches deep(122cm) X 84 inches wide (211cm).
That is a single plant, I planted 12 this year in a raised bed, that was only 26 inches deep(66cm).
I am still making peppers & should get more on into late OCT.

    Bookmark   August 25, 2011 at 8:43PM
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Last time I checked, roots do indeed go well past 12" for most plants. Here is a good reference with diagrams.


Tomatoes - 4 Ft deep

Spinach - 3-4 Ft deep

Strawberry - 3 Ft deep

Even the very shallow vining plants like watermolon or cucumber will achieve depths of 2 Feet plus.

I say do it once and go for it. I have done it for my raised beds (dug 2 Ft below 1 Ft raised beds) and have had pretty good success.

    Bookmark   September 14, 2011 at 1:17PM
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I have pure clay soil and have been adding newspapers to the soil this year. I rip thin strips and bury them and break up the dirt on top. I try to leave some newspapers peeking out to act as a wick for the rain.. The difference in my soil already is truly amazing. The spade goes in like butter in some rows! The worms populations are increasing in those rows like crazy too. They must love newspapers?

I was shredding some this morning and I hit 2 rows that were so odd. The soil seemed fluffy like whip cream? It didn't weigh much and was finer crumbles than the other 30 rows. I think I hit the magical percentage mark in those rows. Maybe they got up to the desired level of 20% organic matter?

It's hard because my garden is 125 feet long and 20 feet wide. It's too much to try to amend this much of an area. Several years, I added 90-100 garbage bags of leaves and tilled them and that did help a lot. Now they don't allow folks to put bagged leaves at the curb and I have none to steal:) And I'm getting too old to rototill because it hurts my arms.

I laid down plastic for the first time this year and started amending the soil ONLY where the rows would be. I left 12 inches of soil between each plastic row and planted the veggies between the plastic. So the plastic is only being used as a weed barrier that I walk on. I will just keep adding more newspapers every year. They decompose almost the same that leaves do (1% difference in decomposed nutrient analysis)

Newspapers are free too and I can bring them home from work by the bushels.

    Bookmark   September 14, 2011 at 4:29PM
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Nevermore44 - 6a

There's nothing like having to dig a hole with a pitch fork and a spud bar! I once used a paddle bit on a drill to "dig" out holes for a bunch of lavender⦠which doesn't mind the cruddy soil once it gets going. You just get odd looks from the neighbors.

My yard is 100% fill clay⦠with many area having the actual gray clay. When i first moved it, it was just sod on top of the fill. Over the years i tried just added compost to the planting wholes and mulched. Most things do okay, but once it gets too dry, I get huge cracks and the plants start to suffer if I don't water a ton. Once summer rolls in and things dry out, I also can't really add a plant without it being a good workout to get a nice hole dug⦠not fun.

So for the past few years, I have been going section by section to amend more deeply. First I move the top 6ins (that I have made better over my years) to the side⦠Then I completely remove 6in of fill below that. It is amazing that regardless of where I dig⦠I will always get a large rock that I have to remove⦠Gotta love fill!

I then add in compost/manure back in with the original top 6in and mix. It is so nice to be able to dig in an area and the shovel doesn't just stop like hitting a brick wall. I had been buying the compost/manure from HD on sale⦠but I just recently found a small township that collect and compost leaves from their residents and then offer back to them for compost/mulching. I stopped by the leave dump to check it out⦠it was 20 feet high and twice as wide. Most of the bottom stuff was nice and composted too. So assuming the residents aren't using them as quickly as they are collected, I contacted the admin folks and they said that I could take as much as could⦠so I am set for compost and mulch for now.

The hard work at the start is so worth the benefits you get later⦠not just in the plants growing better (which apparently might not be long lived)⦠But also less watering.. And it's much easier to add/divide/move plants from that point on.

So my main point is that if you live by an area that does collect leaves⦠ask where they are going! I would think that most places can't get rid of them fast enough for free⦠Kinda like tree trimmers giving away chipped wood.

    Bookmark   September 14, 2011 at 5:49PM
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On a large scale no till farming, they can use plant root systems to aid in breaking up hard-pan. Tillage radish and annual rye come to mind. You can do a search on no-til sustainable farming and get more ideas. On a small scale the same can be done by alternating rows every year.
You can install raised beds and or use other ideas posted above.
Before I would go to the jack hammer, which works very well with a spade bit, you should do a perc. test on the soil. The reason is that certain clays will not let water drain through. So what can happen is that you just end up digging a bog garden of sorts.
You can do the perc. test by simply digging a hole and filling it with water. When it is absorbed or not fill it again and see how long it takes it to naturally drain away into the surrounding clay.

    Bookmark   September 16, 2011 at 2:30PM
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