Vegetable Bed in Blackland Prairie Clay

PoouaMay 2, 2014

I live in an area that has heavy blackland prairie clay soil. When it is moist, it swells; when it dries, it shrinks and becomes hard as a rock. Open fields typically form cracks that are as much as six inches wide and three feet deep during summer; these completely close during the rainy season. As you can imagine, it is challenging keeping a house on this stuff.

I decided to dig a bed that will first hold tomato plants. I've dug a trench 16 feet long, 2 feet wide and about 1.5 feet deep. I'm thinking of putting about a cubic yard of sand or gravel in the bottom and mixing a cubic yard of some kind of planting soil with the now-hard-as-rocks chunks of clay that I dug out of the trench. I expect a raised bed as a consequence, but all I really want to do is grow the biggest tomato plants I can, and use the bed for other plants in following years. How does that sound?

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centexan254 zone 8 Temple, Tx

I would suggest that you dig to at least two feet deep if you want to go with a barrier layer over the existing clay. I dug out two feet deep below my raised bed. I then used about one fourth of the native soil. I amended it with bagged soil, and amendments. It seems to work well so far. Last year I did not dig it deep enough. Tomatoes started great till the roots hit the clay. Then the problems began.

It can be done in just the native soil, just not easily, and yields will not be as good.

If you are planing on tomatoes I would advise using transplants. Otherwise you will not get any fruit till the heat wave of summer breaks. Then it is a crap shoot on if they get to full size before the frost hits.

We have two short seasons with maters in this state. The first is if you protect plants that you get in the ground early enough then you will get some fruit to set before the heat of June starts up. They may take a while to ripen, just be patient. The second season is the fruit set that happens when the heat breaks. If they hit full size before the first frost you can wrap them in newspaper. Put them in a box, and let them ripen. My grampa always called them winter tomatoes as you were eating ripe tomatoes in the winter. The ones that are not large enough to ripen can be batter fried, and the super small cherry sized ones can be pickled.

    Bookmark   May 2, 2014 at 3:34PM
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Thank you for your advice. The trench is still empty, so it would be relatively easy (!) for me to dig another 6 inches deeper. I will say that I have had great results growing abe lincoln tomatoes in 18-gallon containers.

I have about 15 transplants that I'm getting ready for transplanting into the trench. I have a few containers that have tomato plants that I grew from seed, too. I bought a variety of tomatoes, ranging from cherry tomatoes to beefsteak, but most are in the intermediate size. The best producers I've ever grown are the abe lincoln.

    Bookmark   May 2, 2014 at 8:33PM
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earthworm73(WA z8)

Google lasagna garden. It's no dig and produces a very nice garden. It can even turn your crappy clay soil into fertile soil. I should know cuz my house sits on mostly (90%) clay and the garden plot was turned into black rich soil with LOTS of fat worms.

    Bookmark   May 3, 2014 at 12:23AM
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Add a lot of earthworms if you can.

Here is a link that might be useful: vermiculture

    Bookmark   May 3, 2014 at 2:22AM
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Imagine, digging out clay to bring in sand!

Today I'm going to haul some buckets of clay back home (for my sandy garden) from a job site where we hit a rare band of clay. In fact, we have to do just what you are proposing: dig trenches and put clean sand in the bottom before pouring concrete footers.

Other than that probably quite unhelpful story I have nothing to add, since I know nothing about gardening in clays, expansive or not.

    Bookmark   May 3, 2014 at 7:02AM
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PN, when I buried chunks of clay in my sandy garden (about 10 years ago, I since moved to a clay place) it stayed in lumps for several years and contributed nothing. The few earthworms in that sandy spot completely avoided it (I guess they do not like to break clumps either). You have to mix and break it as much as possible.

    Bookmark   May 3, 2014 at 9:28PM
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centexan254 zone 8 Temple, Tx

Also adding a 2x6 frame can help to raise it up a little more. This would give it a better chance with draining as well. I would suggest mulching as well. Your plants will thank you in the heat of the summer. As will your wallet when your water bill is lower as well.

    Bookmark   May 3, 2014 at 10:50PM
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Glib, yes, I've learnt that from earlier attempts. I'll dry this clay in the sun and then pulverize it and mix with garden soil.

Boy, it turned out to be one hard vein of blueish clay, let me tell ya. Impenetrable to a shovel, even the excavator had some trouble with it. Pretty much rock-free, even though surrounded by very rocky gravel.

    Bookmark   May 4, 2014 at 7:47AM
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I had this type of land when I lived in SW OK. When I bought my 5 acres the soil would crack so wide in the dry summers that you could fall in. When it rained you couldn't walk around because it was a slippery mess and stuck to your boots until they fell off.
After a couple of years of piling up tons of stall cleanings from the horses on every part of the property it was fertile and had beautiful top soil. I literally dumped wheelbarrows full everywhere and let them compost in place. My peach trees were amazing!
What I'm saying is that if you want to start a garden area for the long haul, starting with a truckload of horse manure and wait until it's fully composted to use that area of the garden. In the meantime a small, raised bed with bought soil and compost should do great. I'm not sure you even have to dig down. In fact, digging down may cause your drainage to be far worse.
I have my current raised beds on the surface of extremely compacted clay and after four years of amendments I'm finally starting to be able to dig down into the surface of the soil.

    Bookmark   May 4, 2014 at 10:40AM
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Thanks for the replies!

My plan now is to wait for the rain forecast for this weekend to wet my dirt, which usually makes it crumbly, then mix it with the garden soil I've bought.

Oddly enough, I've encountered a lot of earthworms while digging this trench. I wonder if they are related to the batch of nightcrawlers that I dumped in my compost heap the first year? They are on the other side of the yard, most of which is covered by plastic sheets and dirt on top of the sheets.

    Bookmark   May 4, 2014 at 7:00PM
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