cover crop for help hard clay soil

iamtryingJuly 22, 2009

Does anyone out there know which cover crops are best for breaking up hard clay down deep? I think I read somewhere about some type of grass or grain whose roots could penetrate a couple feet through hard soil.

I have a small fenced area in which I am planting several 4x8 raised beds. The soil is all fill dirt that was excavated from a neighbor's building site and dumped behind our house. We live on the side of a small mountain in western NC and the land behind our house dropped off so steeply that it was very difficult even to climb down. When the property owners adjacent to us decided to build their huge log home, he needed to get rid of allot of dirt, so they asked us if they could dump it behind our house. NINETY truck loads later, we have a respectable back yard, and I have a spot for a garden.

The bad news is the fill dirt is all clay with lots of rocks. For my first four raised beds I dug down about 16 inches. I replaced the dirt with composted manure, peat moss, vermiculite and a little of the clay minus the rocks. I built a frame for the bed using 2x4s so when I filled it to the top I had about 20 inches of excellent soil. Things are growing great, but that was a LOT of work and buying the vermiculite and peat moss got expensive.

For the next beds, I'm wanting easier. I'm thinking of not digging at all - just laying the 2x4 frame right on top of the ground and filling it with my soil mixture kinda' Square Foot Garden like. Let earth worms and nitrogen fixing cover crops do all the hard, deep work. I know I won't have the same good results right away, but, dang, I'm tired of digging.

Anyone out there have any nitrogen-fixing wisdom for me?

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Since you are almost there, you could spend the extra $ and get favas (Banner, at Territorial Seeds for example). They are almost certainly the best cover crop for you bar none. First, they fix much more N than any other legume (triple what beans do), so come next spring you will only need to add some wood ash for P and K. Second, they have a deep taproot, and because they grow six feet tall, I am sure they will go down at least a couple of feet.
Obviously, they will produce enormous amounts of organic matter. They specialize in clay soils, do poorly in sandy soils, do poorly in heat, they are hardy to 10F, and tolerate waterlogged conditions.

The drawbacks are the cost (the seed is quite large, so it costs money) and also I am uncertain about the planting time. Favas really are the perfect winter cover for zones 8-9, going October-April and providing food and fodder besides all those goodies above. In your case, you may have to try in September, and if they die, try again in February. In Michigan, Zone 6, I plant under cover in February (for food). Cut them in May and plant immediately.

    Bookmark   July 22, 2009 at 11:06PM
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glib - thanks for that. I'll do some research on the best time to plant favas in this area.

    Bookmark   July 23, 2009 at 10:33PM
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aztomn(SE MN 4a)

glib: What does it mean when you say "plant under cover"? I live in MN where it is terrible cold. Do you know if it is viable cover crop here in an open garden, say fall or early spring?

    Bookmark   July 23, 2009 at 11:09PM
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I mean I plant in a hoophouse. Surely it is viable even if the favas die. You will still get organic matter, just less. In MN they will die, of course. Perhaps in your case it is best to use oats or clover? Oats are usually planted knowing that they will be cold killed. They cost less and are more adaptable. Less roots but still a lot of above ground matter. Anyhow, look at those companies who have cover crops for the home gardener, and see what they have. Do you need biomass, N, or deep soil breaking?

    Bookmark   July 23, 2009 at 11:36PM
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aztomn(SE MN 4a)

Hoophouse - Duh! Under cover made my mind wander.

I've been thinking of using a cover crop mostly because weeds grow before and after frost. Something is gonna grow, assuming it should be with benefits. And I do believe my soil is mostly hard clay (is there soft clay?) and compostables. I have researched it for my area, but only ended up with information overload and forgot why I was searching.

I apologize to iamtrying if I'm overunnig his/her question with my own.

    Bookmark   July 24, 2009 at 12:26AM
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The problem with clay fill is not going to be solved by a taproot-clay will recompact almost as soon as the root dies. In fact, your annual freeze-thaw cycle is going to do more for loosening your soil than an oak tree's taproot! What you need is a heavy yielder of organic matter that you can till under and a bonus of N fixing would be super.

I would recommend something like red or crimson clover (red is hardy to -30 F-zone 4). You can even plant these with some cool season crops like broccoli, spinach and others that grow above 8" tall (just underplant with the clover). Both clovers can be treated as winter annuals in zone 6. Mow them in early spring and till under, then plant your spring and summer crops in a week. Repeat each winter (unless you want to grow some greens!) and you will solve your clay problem over time.


    Bookmark   July 24, 2009 at 3:43PM
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aztomn(SE MN 4a)

Steve, that sounds like a good idea! I thank you for "making a decision for me"! :) I'm going to give that one a try. Much appreciated!

Definetly trying to throw everything at it I can to remedy the clay situation. Understanding the best route to take is several seasons of adding compost. Soil tests ok for most everything EXCEPT organic matter. Starting just this year so hoping to get there ASAP, as mother nature will allow. A tilled-up, neglected lawn is not what anyone refers to as an "Ideal" garden bed.

    Bookmark   July 24, 2009 at 4:18PM
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steelshepherd(6 OH)

It sounds like your first beds are overly amended to the point that roots wouldn't want to leave the bed and spread into the clay. This is a very real phenomenon. It can also act like a bathtub in heavy rains. Roots and water move best through uniform soil.

I'd mix 1/2 the amendments from your first beds into your new ones and put ome clay from your new ones into your old ones.

I too have very hard clay, but my garden beds are rich and friable due to years of composting and NOT walking on the beds!!! Ammended clay WILL NOT simply re-compact itself when the root dies. When I fork up a big hunk of clay in spring, there are channels all through it left by roots, worms, bugs, etc. It's wonderfully crumbly.

My dog trampled lawn on the other hand... you could make pottery with the clay if you can dig in it.

    Bookmark   July 24, 2009 at 8:36PM
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Hello from a northern MN Lori! I have terrible compact clay. I do have some clover I grow in the back, but it's just to attract bees.

I have tried gardening just in my soil, with some sandy loam and composted cow manure. Nada luck.

This year my dear hubby built me a raised 4' x 12' concrete block garden. I went with Mel Bartholemew's Square Foot Gardening method and mix.

Unbelievable! My peas are almost 7 feet tall! My broccoli was wonderful. Everything else grows like crazy too!

For those of us in cold climates, with short growing seasons, I would recommend the Square Foot Gardening method as the only way to go!

    Bookmark   July 24, 2009 at 10:06PM
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If your interest is mainly in making the soil easier to work, you might also try adding a very thick layer of mulch.
Last summer, I moved into a rental with hard compacted clay. I saved all my lawn clippings and spread them about 6 inches thick where I had planned to have my garden this year. I decided to have a bigger garden. The difference between working the soil that had been mulched and the soil next to it was amazing. The soil under the mulch sliced like butter up to 18 inches deep. The stuff right next to it that had not been mulched required a pick axe to get deeper than 6 inches.

    Bookmark   July 26, 2009 at 12:09AM
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Since you asked about cover crops;hubby tills his veggie bed in fall after the crops are out ,then scatters winter rye seed over it all and waters it stays green all winter ,,,then he tills it in for spring planting.He calls it green manure.Has anyone else done this?

    Bookmark   July 26, 2009 at 12:39AM
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Winter rye is inexpensive, germinates quickly and makes it through a cold winter. It's great stuff. BUT, be sure and till it in when still green, do not let it go reporductive and form grain heads. At that point it can be difficult to till it in. Tom

    Bookmark   July 26, 2009 at 6:54AM
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