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A big stupid rock shelf where I want my food forest!

 
master pollinator
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Location: Central Texas USA Latitude 30 Zone 8
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This morning I was digging a hole where I want to plant Asian Persimmon in my food forest and I hit a big stupid rock shelf.  These shelves are prevalent on our place here and a feature of the region as a whole.  It's a rocky place.  This darn shelf is only about a foot down.  Is it hopeless to want to plant persimmon trees here?  Are they doomed to die in a drought?  There are native persimmon right nearby, as well as elms and another native fruit called Gum Bumelia.  Is there a different domestic fruit tree which would be more suitable for dry rocky conditions?
 
gardener
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Location: Arkansas - Zone 7B/8A stoney, sandy loam soil pH 6.5
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hau Tyler,  some things to ask yourself in such a situation.

How thick is this rock shelf?  Can I break through it?  Do I want to expend the time and energy to break through the rock shelf?  What are the root growth patterns of the tree normally?

Our Persimmon trees do just fine in shallow soil areas since most of them are in 2 feet or less of soil, on top of the mountain. They do not have a "Tap Root".
My biggest concern for our trees is wind blow down. However, they withstand up to 60 mph winds right now with no problems, so they most likely will continue that trend.

Persimmons do best with a lot of decaying wood surrounding them.
This also means that as the wood rots down, soil depth goes up (not a lot, but over years of giving the trees what they want to thrive, it will end up significant probably).

We have one tree that is in 4 feet of soil, the feeder roots of this tree are only 18 inches deep max. there are a few fastening roots that go deeper but they only serve to fasten the tree to the spot.
Fastening roots will go down till they are stopped, at which point they will turn and grow along until they find a place they can go deeper, cracks are one of these go deeper places.

You may find that planting there requires some watering, at least in the first few years.

Redhawk
 
Tyler Ludens
master pollinator
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Location: Central Texas USA Latitude 30 Zone 8
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The trees naturally grow along the top of the shelf and are sometimes able to find cracks through to deeper layers.  Thank you very much for the tip about decaying wood.  Perhaps I can build the area up a bit with buried wood to get a little more soil depth.
 
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Is the shelf level or does it have some slope to it?  I'm guessing here, but if it has some slope, might it carry water that has percolated into the soil downhill to your tree?  I'm speculating again, but what if you dug a curved trench right down to the shelf on the downhill side of the planting spot.  Then bury wood there to act as an underground water dam and a rotting water storage medium.
 
Tyler Ludens
master pollinator
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That's a good suggestion!

 
pollinator
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Hey Tyler

I don't know a thing about persimons.

English is not my native language. What do you mean with a 'Rock shelf' ? Is it a Rock layer ? ? If so you might want to check orientation of the geological layering (like Mike Jay said) (trough observation, maps or by measuring) The wiki link shows what i mean. https://en.wikipedia.org/wiki/Structural_geology

If you live in an area with sedimentary layers. Sedimentlayers with different characteristics are most likely within reach. Sedimentlayers are seldom uniform.


Also good to know.

Almost any rock that has been deep in the earth crust, breaks along joints that allow water and roots acces to deeper levels. Joints also for due to extreme temperature differences https://en.wikipedia.org/wiki/Joint_(geology)

Joints are also favoured spots where rocks wheather faster. F.e. limestone dissolves faster along joints.


Finding weak spots such as joints may be done by proding using a piece of smooth rebar iron with a sharp end.




Erwin
 
Tyler Ludens
master pollinator
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I'm going to try to continue to excavate and see if the shelf is made up of large rocks that can be pried loose.  This was the case with some other holes.  
 
pollinator
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I have my macadamia nut trees planted in my pahoehoe lava field which has 6" to 10" of soil atop the lava shelf. My concern was that they might blow over when they grew big. So I brought in a hydraulic hammer on a skid-steer and hammered (that is, fractured) the rock in a 10'x10' area for each tree. And while at it, I had a small hole hammered for the tree so that I could get it into the ground. The plan worked perfectly. The trees are now 10' tall and really producing well. Only one blew over in the severe wind storm we had two years ago. The rest developed good anchoring roots through the fractured rock.

Don't know if this method would work in your area, but it's something to consider. By the way, I had 30+ areas hammered for the same price that 7 would have cost me, so I now have plenty of future sites waiting on the sidelines for future trees.
 
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Location: Western Kentucky - Zone 7
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You can grow fruit trees on mounds just fine. Trying adding a two foot mound and growing on it.
 
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How about grafting onto the existing native stock that is already in the ground?
 
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