Digging an in-ground garden bed into the dense clay soil of my backyard

[MattWott]

I've documented my experience digging an in-ground garden bed into the dense clay that my home was built on in the north east Austin, TX area.

Most contractors in the Austin Texas area use dense clay to stabilize new home foundations, especially for homes built after 2015. My backyard had a ton of this clay, and building an in-ground bed was a major pain.

I highly recommend buying the following tools to get the job done correctly:
A sturdy flat head pickaxe.
A quality 48 inch round tip shovel, if you don't want the shovel to break, try paying more than 15 dollars.
A quality wheelbarrow with two wheels, this will be so much more helpful than a wheelbarrow with one wheel, the two wheels provide necessary balance when moving heavy clay.

I've started a Youtube channel called "Austin Texas Gardening" for more detail, see the video below -

 

[Marck]

As an alternative to soil replacement, I would suggest incorporating large amounts of organic matter into the clay. Even seemingly impossibly dense clays can become highly fertile garden soil if properly amended and managed. Most clay-based soils actually have many advantages such as nutrient richness and moisture retention

 

[Oliver Buckle]

If I dig a hole more than six or nine inches deep in my clay garden I quickly find myself with a small pond. Like Marck says, clay is not all bad, it stops things drying out and nutrients leaching away, but it needs to be ammended. My solution is to burn some of the clay to terracotta and add compost. It is not instant, but it seems to be working well.

 

[Esther Knapicius]

Yep, been there with the dense clay. its take out and replace and a good tiller. we also have large stones, and rocks. thank goodness we did all that with younger bodies. good luck.

 

[DirtMechanic]

If I dig a hole more than six or nine inches deep in my clay garden I quickly find myself with a small pond. Like Marck says, clay is not all bad, it stops things drying out and nutrients leaching away, but it needs to be ammended. My solution is to burn some of the clay to terracotta and add compost. It is not instant, but it seems to be working well.

Explain please? Do set fire atop the soil, or dig it up to add to a fire? What is your method? There are baked clay products like Turface that have gotten my attention, but that seems expensive.

 

[Oliver Buckle]

As I work the soil I get balls of clay about two or three inches across, though sometimes they start out as bigger chunks of clay I have dug up and broken up whilst digging in other stuff or hoeing. I gradually rake them together into one corner of the bed, the ones that are not clay break up in the process. Then I fill flowerpots with them and leave them in the greenhouse to dry out. When I have a fire I use an incinerator to get a decent heat and then chuck in the balls of clay. It needs about 5-600 degrees to sinter clay I am told, if I put too much in at once it won't burn as hot, but get it right and it changes to a much lighter colour. I usually break the pieces up a bit before I add them back, but hoeing and digging does it in time.

 

[DirtMechanic]

As I work the soil I get balls of clay about two or three inches across, though sometimes they start out as bigger chunks of clay I have dug up and broken up whilst digging in other stuff or hoeing. I gradually rake them together into one corner of the bed, the ones that are not clay break up in the process. Then I fill flowerpots with them and leave them in the greenhouse to dry out. When I have a fire I use an incinerator to get a decent heat and then chuck in the balls of clay. It needs about 5-600 degrees to sinter clay I am told, if I put too much in at once it won't burn as hot, but get it right and it changes to a much lighter colour. I usually break the pieces up a bit before I add them back, but hoeing and digging does it in time.

That is pretty advanced, Mr Science Guy! I am impressed! I hope to create a large rocket stove to eliminate a lot of waste wood here, and that type thing might well be part of the use of energy. Except I do not see me hauling clay uphill. I was thinking the stove lighter than the wood so I could take the stove to the various woodpiles. Now I am complexed again, not that that takes very much to accomplish, but it would be a really cool thing to do with that heat besides just charcoals.

 

[Oliver Buckle]

I used to know two guys who made small brass models for the mantlepiece. To melt their brass they had a forty gallon drum and made a roll of lino to fit inside it, then filled between the lino and drum with clay before filling the lino roll with coke and suspending a crucible in the top. Then they lit it at the base and attached an old vacuum cleaner on blow. That sounded like a rocket taking off Don't forget the potash in your wood ash, well worth having.

Regarding the OP, my fear is that he may create a pond filled with sodden mud when it rains, clay won't drain. By digging and letting the weather break it down a bit, then adding things to it, the level of friable earth rises above the ground level and still drains.

 

[Marck]

Yes, but don't conflate clay with undrained saturated soil. Clay will drain if there is a place for water to go, and conversely, many saturated bottomlands will have areas of saturated sand. Clay has unfairly become a monosyllabic shorthand for all drainage problems.

Of course, ultimately this whole debate depends on which plants one intends to grow, but most general gardening including vegetable gardening should not require any such soil removal. Most should focus their efforts on mounding with moderate soil addition mostly in the form of organic matter, though mineral components have their place as well. Many people choose to remove and replace soil for what amounts to only basic landscaping, and that seems like a pointless waste, especially since these beds will have their own additional maintenance demands and pest concerns that could be avoided by working with the native soil and environment.

Not to speak on both sides, but yes, I have built several large 'rockery' beds, half-raised, half-sunk. These are intended for a variety of unusual succulent and other desertic or alpine plants, that really do want sharp drainage. Also, any soil removed, found new purpose onsite, much of it immediately outside the beds to stabilize the walls. However, in truth, I grow a much larger variety of plants in my amended clay, including many other succulent, arid, and Mediterranean-climate species.

 

[Chuck]

For all of you folks posting on this thread let me try to explain what the OP is dealing with. It is NOT clay soil. It is a calcium carbonate called caliche. This stuff is mined for cement. Limestone is often found layered in this "soil". Very often a layer of limestone is actually the surface and the caliche lies underneath. Caliche is actually a sedimentary soft rock Aside from cement it is also used as road base. When packed or rolled it becomes almost waterproof. Otherwise water will drain, fairly slow through the sediment and rapidly through cracks and fissures. Ranchers here in Texas build small lakes and ponds and use packed/rolled caliche to waterproof whatever they are building. Caliche is extremely alkaline, usually around a Ph of 8+. Even when mixed with a good compost it still makes an extremely poor growing medium for most plants.