hugelkultur vs sunken beds

What is better, hugelkultur or sunken beds? My situation is as follows, but I am guess hugelkultur will be better.

I moved into a new home in a small town on a fairly small lot. It just has a lawn and a pine tree. But I am looking at setting up a food forest. The is annual 14 in of precipitation. However most of it is in the fall/winter. The summers here are hot and dry. My soil is some topsoil (I am guessing imported) over silty clay loam over basalt. The area behind my basement retains some moisture, but much of my property is on a slight slope and will get bone dry in the summer without irrigation.

I moved to this place because it is walking distance to my work.

I think, with suitable forethought, that hugelbeds would work well. You could even do a "sunken" hugelbed too. If you follow the hugel idea, you could set your situation up any way that suits you.

I have installed buried wood beds throughout my kitchen garden and it has done much better in drought than mulched beds with no wood. Because I keep adding organic material, the entire garden is somewhat raised, with paths made of deep wood chips. So this is working well for me. I haven't yet been able to test hugelkultur (mounds) yet. I made a couple hugelkultur last year but they have not yet gone through a summer with plants in them. So far they're failing because armadillos dig in them. I have some other raised wood beds in a more protected part of the garden where I hope to see how they do with fruiting shrubs and other plants in them.

More details in my project thread.

I'm a newbie and my advice is purely theorhetical. So, with that caveat out of the way:

You live in a very dry area, so I don't think any raised bed is a good idea. Instead of hugel mounds, you should build hugel swales. Dig a trench where you want your garden, fill it with wood, then bury it. The result will end up slightly higher than the rest of your yard; that's okay because the real action is happening at the roots, not at the surface.

Because your area is so dry, you need your system to soak up and store a lot of water. To accomplish this, I recommend that you bury as little good, useable wood as possible. Go out in the forest and find old deadfalls that are starting to show signs of dry rot. Partially-rotten wood will absorb more water in less time than fresh logs or finished lumber. If you use new, fresh wood, you'll add a year or more to the time it takes for your garden to mature and produce the amazing yields we all read about. But whether you use new or old wood, I think you'll be impressed with the drought-resistance of such a bed.

My hugel beds warm up faster, just as my raised beds do. If my growing season weren't so short subsurface hugels would probably work just fine. I do dig down when I start a new hugel bed usually a bit deeper than just removing the sod so essentially I am already creating a swale.

I'd go fairly deep in this case. 15" a year isn't a lot of moitsure. Dig down so you can capture as much of that water as possible. If your yard is on a hill, dig perpendicular to the slope.

How deep until you hit basalt?

Do you know if it is permeable? Does the water go down through the basalt or does it run downgrade along the surface of the basalt?

I have a similar thing with impermeable sandstone. I have had great luck building woody bed swales on contour OF THE SANDSTONE, not the surface contour. I adjust the surface contour to match somewhat, but it is the impermeable layer contour that really drive the hydrology for me.

I figured out the contour of the sandstone by observation and digging a lot of post holes. I dug my beds all the way to sandstone, lined the downhill side with clay, and filled with wood.

Learning this has allowed me to capture the rain that runs off my neighbor's property, effectively giving those beds 3 times the yearly rainfall.

Now there's an interesting concept, and one that never occured to me. Here in southern Michigan, you have to dig deep to hit solid stone of any sort. By "deep" I mean that it's not a problem when digging out basements for houses. After a few inches, it all turns to clay.

It was a shock to me. Went to dig the foundation for my house, hit it in one corner at 8 foot down. 20 feet away, they hit it at 4 ft trying to dig the septic. Much of my garden space is 18-36 inches. I was cussing it for years until that hydrology hit me. THE PROBLEM IS THE SOLUTION.

So how did you determine the contour of the bedrock? GPR can get rather pricey.

Chris Watson wrote:So how did you determine the contour of the bedrock? GPR can get rather pricey.

By digging holes for posts and trees and foundations. I hit bedrock at 8 foot for the corner of my house, at 5 foot for my septic, and 18 inches when I tried to put in a clothesline. That was on ground that contoured from east to west on the surface, but learned the bedrock goes west to east.

You don't have to be exact, but just knowing it is possible and looking for it can lead to greater understanding. I now can capture more of that water in my beds. I think this is also why some people have so much sump pump problems even though their surface slope and drainage is perfect--they run all the water well away from the house on the surface but then it soaks down to the impermeable layer (rock or clay) and flows back to the foundation.