Help with Clay Topsoil

June 17, 2008 2:26 AM

The soil in my tiny yard is hard as concrete, but I want to grow a garden. Tips?

I got me a pick axe, and a box o' gypsum. I'm set to start hammering my little chunk of soil. Can anyone recommend some soil improvers or techniques for making awful topsoil vegilicious? I'm working a plot about 8'x15' and I'm an utter novice.

posted by maryh to home & garden (19 answers total)

Raised bed gardening could be your best bet.
posted by Daddy-O at 3:04 AM on June 17, 2008

Rent a small tiller. It will do a more uniform job of breaking and aerating compacted soil, than any manual tools, with a lot less work. Till in plenty of appropriate soil amendment. Test your amended soil, and correct pH problems. Add fertilizers appropriate to the kind of plants you want to grow.

Good gardeners quickly learn to think in seasons and years. You can't make great soil instantly.
posted by paulsc at 3:11 AM on June 17, 2008

Tillers will aerate, but only to like 6 inches of depth. Double digging is back-breaking, but works extremely well. When I lived in Silicon Valley, I rented a house with a backyard with great light, but the soil was like adobe clay. We ran a sprinkler for a few hours at night for a few days, keeping the area covered with black plastic during the day to take out the weeds/grass. Then we double dug. The resulting garden was spectacular. Totally worth the work.
posted by plinth at 3:47 AM on June 17, 2008 [1 favorite]

Esther Dean pioneered the no-dig method for gardens - here's a step by step how to.
posted by strawberryviagra at 5:03 AM on June 17, 2008 [1 favorite]

Don't break your back. Do as Daddy-O suggests or there is also the Square Foot Garden.
posted by JJ86 at 5:46 AM on June 17, 2008

If your soil is that hard, it is probably severely lacking in organics to "fluff" it up, and will not grow plants well. In fact, my bet is that it will return to concrete after your first rain.

Break your earth (necessary for drainage) but do not till. Build raised beds (at least 10-12" tall) over the broken earth and fill them with a mixture of compost and soil. (You can get these in bags or in bulk from your local nursery/Home Depot.)

Do you get a lot of rain? Mix compost 50/50 with potting soil. Do you live in an arid climate? Mix compost 50/50 with garden soil.

It's a bit late to plant by now, but if you got starts from a nursery, this method would let you have a garden this summer instead of next year.

The only other thing to do, if you don't want the expense of raised beds, is to till in a s***load of compost. And I do mean a s***load. The amount of compost you use is directly related to the amount of veggies you expect to get back.

If you're going to try and till your own soil also use (sparingly) a fertilizer that advertises that it includes microrhyzae, which over the years may help break up your soil naturally.

Also, plan paths and beds and never, never step on the soil of the beds. That will help avoid compaction too.
posted by GardenGal at 5:48 AM on June 17, 2008

I'd lean towards the raised beds as well, but if you don't go that route, double dig and amend with lots of compost. You'd also be well served to start composting your own plant wastes. Why pay to throw it away and pay to buy some back?
posted by advicepig at 6:38 AM on June 17, 2008

I wonder if the fungi perfecti method of soil improvement would help here. Would be an interesting experiment, anyway -- I'd go ahead and call them (after reading that page). They seem to have super-intelligent, informed people manning the phones, anyway, and could probably let you know if their products would help.
posted by amtho at 7:30 AM on June 17, 2008 [1 favorite]

We have the same problem in our garden. The soil is like rock. I think you can fix it. Get a Garden Claw or something similar. Mix a loose compost in - I like Cotton Burr compost because it's loose, chemical free, and provides good drainage. Add a topsoil with a lot of peat.

You might also try Lazy Man's Gold, which is supposed to aerate soil with a hydrophilic/hydrophobic action and increase beneficial bacteria. It's hard to tell if it's working because I've done a lot of stuff to the garden, but I figure it probably doesn't hurt, and things have been going well in the yard.
posted by walla at 8:21 AM on June 17, 2008

Short-term fix: Spend some cash to buy a truckload of topsoil. Or start doing some container gardening while you think about the clay problem.

Longer-term: Read up on permaculture and composting. Try to understand how your soil became so barren. It sounds like you need to capture water. Do you get huge downpours that wash all organic material away and then hot sunny weather that just bakes the soil into concrete? As has been said, renewing the fertility of the soil is a process that will take years - but will become a self-regulating system - so you don't have to do this again.
posted by kamelhoecker at 9:58 AM on June 17, 2008

If you do a digging project what you're looking to add-in is called a "soil amendment", and a landscape supply company near you may even sell a custom mix of exactly what the soil type in your area needs. It's not topsoil, for clay it's going to be course organic material--mostly manure probably, wood bits, etc. that will blend with the mineral rich clay to form a perfect garden soil. Maybe call these guys. I've amended a clay front garden and it's back breaking, but the result is amazing--be sure to dig deep. You'll need to have the stuff delivered by the truckload.
posted by tula at 10:36 AM on June 17, 2008

Oh - you needed to read the steps in the link post that answered your entire question:

This is a recipe for a No-Dig Garden as developed by Sydney gardener Esther Dean in 1970’s which is basically a garden above ground made up of layers of organic matter that rot down into a nutrient-rich living soil. It is much like making lasagne adding one layer upon another until the desired thickness.

The bed will break down into a nutrient-rich soil, so it will need to be kept topped up with fresh layers of organic matter. Why dig a garden the conventional way when there are millions of worms willing to do the work for you.
posted by strawberryviagra at 3:42 PM on June 17, 2008

If you've got a yard of dense clay like I did you've got to dig. It's nothing to do with convention; it's a matter of density and giving the worms head start.
posted by tula at 5:03 PM on June 17, 2008

a head start.
posted by tula at 5:04 PM on June 17, 2008

If the soil is as bad as you say, but you want veggies this summer, do raised beds. Otherwise you will be doing far more work than is necessary digging and amending and wasting water trying to loosen your soil. In the fall, disassemble your beds, spread the soil, and spread a 4" laver of good compost, then sow alfalfa seeds. Alfalfa has a very robust root system that helps to break up clay, improve water and air penetration, and provide nutrients (particularly nitrogen) to soils. In the spring, rent a tiller and till the alfalfa into the soil, along with the compost.

Gypsum will not help with drainage in clay soil unless that soil is sodic (contains sodium). You would need a soil test to determine if your soil contains sodium. Sodium causes clay particles to disperse, and gypsum solves this problem when the calcium in the gypsum (CaSO) takes the place of the sodium on the clay particle, and allows the sodium to leach away. If you don't have sodium in your soil, it's likely that calcium already exists on those receptors on the clay particle, and the additional calcium from gypsum won't do anything to improve soil aggregation. I know garden centers will tell you otherwise, but they just want to sell gypsum. To improve drainage in clay soil by increasing aggregation of the soil particles, add organic material.
posted by oneirodynia at 8:51 PM on June 17, 2008 [1 favorite]

June 12 Los Angeles Times has an article:

How do his veggies grow? The no-dig way

The article describes a garden made by layering hay, fertilizer stuff and compost. Over time, the mixture breaks down, but he gardens in it from the start.

I recall a similar article in Mother Earth News or Organic Gardening (can't remember which) in which whole bales of hay were used as pre-built raised-bed gardens. Holes were chopped into the bales, and soil added as if they were pots. Plants put into these holes would spread roots throughout the bale. Eventually breaks down into compost. Over time, and several seasons' of added bales, the result is a raised bed of compost/soil.

These two methods avoid dealing with the lousy soil altogether, and let you plant in a self-supporting medium above the soil. Gradual decomposition and leaching leaves an area of good soil for future gardening.

Disclaimer: Never tried these myself.

Here in southern New Mexico, I work at the state university. Our experimental farm has such amazing soil. I once hit a big clod of dirt that had dried on the side of a furrow. It made the shovel ring like a bell. Very hard stuff.
posted by DanYHKim at 11:10 AM on June 19, 2008

Coffee grounds are really good for compost and creating new organic matter. Just dump them on in, might do some good for your soil.
posted by RobertDigital at 1:30 PM on June 19, 2008

This is what I do with my unyielding clay soil, which I can't dig more than an inch or two into with a shovel. No pickaxe needed.
Make an itty, bitty depression in the ground. (about quart size, maybe)
Fill with water.
Wait for water to be absorbed.
Dig out the moistened soil.
Fill with water, repeat.
Always, always wait until all the water is absorbed to dig -- otherwise, Bad Things happen to soil, and it gets weird and lumpy.

I don't know anything about the raised bed method, but for bigger plants/trees you will need to dig down.

You'll also need to mix something with the soil. People above seem to know more about that than I -- but gypsum? I think the reason soil in my area is so hard is that it already has plenty of gypsum. It's the last thing I'd add to the soil to grow plants, but maybe it's different where you live. Which reminds me -- it might rain where you live, and you could just dig after it rains when the ground is soft. If you have a local agricultural extention service or master gardener hotline, they might know more about what the ground is like where you live and what you need to do.
posted by yohko at 4:59 PM on June 19, 2008

Actually coffee grounds are great as a direct soil amendment and texurizer, plus if you have a lot of Starbucks and other coffee bars in your area they are free for the taking. I always look for things that I can get for free, lawn clippings from lawn care companies, leaves (in the fall) from the same, I once had a guy who raised pigs living very close to me and I had some really good gardens at that time, I would walk over to his barn with a wheelbarrow and load up. Take a close look right around you and you might find many sources and resources that others regard as trash and a nuisance.
posted by leron at 11:24 AM on June 20, 2008