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Decomposed Granite/Bentonite Question

 
Bruce Drukker
Posts: 23
Location: Fallbrook, CA (San Diego County) Zone 10a
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I live in an arid climate with an annual rainfall of about 16 inches. We actually buy our water over here and it is quite expensive, so I was really exited to learn about Hugelkultur. I have access to an unlimited supply of avocado wood which I'm assuming will work in this system. Problem is, my soil is decomposed granite which drains incredibly fast. Add to that the high, dry heat and a lack of rain and you can see my predicament. Seems to me that without adequate moisture, the wood will take forever to start decomposing. I have been toying with the idea of lining the bottom of the beds (roughly 3'x6', 30" deep) with bentonite to try and retain some moisture between rainfalls. I am new at this and am still in the planning phase, so perhaps I should abandon HK altogether, I'm not sure. Any advice would be greatly appreciated!!

Cheers!
 
John Elliott
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You don't have to get that fancy to spec bentonite, any old clay will do. And there's plenty of clay to be found in your area, just look for an old Spanish mission and take your bucket and shovel and dig there. Or if you have a litter box trained cat, there's a constant supply of useful clay -- and it even has nitrogen added to it!

Granite is really nice to have, because it provides minerals that are lacking in a lot of other soils. One other thing that will help with the water situation is to add biochar in with your hugelkultur project. I know that in your area, having an open biochar burn would give the locals fits, so maybe you can disguise your biochar burn as something else. Fill a Weber kettle with some of that avocado wood, set it to smoulder with a little draft up through it, and tell people you are smoking some brisket.

If you get a good mix of biochar, avocado wood, and clay in with your mostly granite soil, it should respond well for you.
 
Bruce Drukker
Posts: 23
Location: Fallbrook, CA (San Diego County) Zone 10a
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Hey John, thanks for that! I'll look into the clay/biochar thing more closely, I never really thought of it. Yeah, you wouldn't know by looking at it, but there's plenty of stuff that seems to grow great in DG. I have a south facing slope that I'm planning to fill with heirloom melons at some point. Most folks around here are growing avocados and citrus, so I see an opportunity. See you on the forums!
 
Robert Ray
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Location: Cascades of Oregon
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Hi Bruce,
My soil consists of pumice and is very porus as far as water retention and sounds like we are about the same on rainfall. I was amazed at the degree of water retention that occurred with just the hugel mound. The addition of clay and bio-char might be something I try in future beds but those I have constructed without are preforming incredibly.
 
Dale Hodgins
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Robert Ray
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My excavations have only been 1-1.5 feet deep or at ground level. I haven't done any pits because I shoot for solar gain from the raised structure.
 
Bruce Drukker
Posts: 23
Location: Fallbrook, CA (San Diego County) Zone 10a
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Robert Ray wrote: Hi Bruce,
My soil consists of pumice and is very porus as far as water retention and sounds like we are about the same on rainfall. I was amazed at the degree of water retention that occurred with just the hugel mound. The addition of clay and bio-char might be something I try in future beds but those I have constructed without are preforming incredibly.


Hi Robert, that's very reassuring. One of the main points that has kept me up to now from delving into any agricultural venture is the exorbitant price of water. I'm aiming for about 30 inches of depth for my beds and was thinking about sheet mulching the top up to about 3 feet. I'm starting to feel pretty good now, thanks!
 
Robert Ray
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With that much organic material I think you'll notice just how much of a sponge that material really is. You might look into some of the self watering bed threads as well.
 
Tim Southwell
Posts: 116
Location: Hamilton, MT
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Bruce,

My conditions are similar... I sit on an evergreen mountainside of decomposing granite and crushed bedrock with average of 12" annually. I planted 26 apple trees in the fall of 2012 on a 45 degree slope which was rendered barren a few years back by a NF fire. I choose to first build scallops swales with the opening towards the uphill, so that any precip / snow melt would catch in the swale. Prior to planting these 5 gallon pots, I dug down twice as deep as the height of the 5 gal bucket and placed rotting wood (This is a practice utilized in the dry parts of Uganda which is referred to as a Zia (Zy) Pit). Once planted, I covered with either wood mulch or grass mulch. That's it. We had a horrible year in 2013 with less than 10" of precip, and the apples all held fast.

Good luck!
 
Bruce Drukker
Posts: 23
Location: Fallbrook, CA (San Diego County) Zone 10a
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Robert Ray wrote: With that much organic material I think you'll notice just how much of a sponge that material really is. You might look into some of the self watering bed threads as well.



Hmm... Because this is something new for me, I sort of have to speculate. From what I've read, the mounds tend to shrink some as the wood settles and decomposes. Same for the sheet mulch. When all is said and done, I'd like to have mounds that are between 18 and 24 inches tall. I'll check out those threads you mentioned. It is possible that I'm overdoing it. Thanks for taking the time!
 
Bruce Drukker
Posts: 23
Location: Fallbrook, CA (San Diego County) Zone 10a
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Tim Southwell wrote:Bruce,

My conditions are similar... I sit on an evergreen mountainside of decomposing granite and crushed bedrock with average of 12" annually. I planted 26 apple trees in the fall of 2012 on a 45 degree slope which was rendered barren a few years back by a NF fire. I choose to first build scallops swales with the opening towards the uphill, so that any precip / snow melt would catch in the swale. Prior to planting these 5 gallon pots, I dug down twice as deep as the height of the 5 gal bucket and placed rotting wood (This is a practice utilized in the dry parts of Uganda which is referred to as a Zia (Zy) Pit). Once planted, I covered with either wood mulch or grass mulch. That's it. We had a horrible year in 2013 with less than 10" of precip, and the apples all held fast.

Good luck!


That's Brilliant! I have plans for peaches and plums as well as apples. This sounds like just the ticket. Did you remove the trees from the buckets prior to planting? The reason I ask is that I read recently that one can control the size of the tree by leaving it in the bucket. I guess this would make the tree root bound, so it kind of makes sense if you want dwarf trees.
 
Robert Ray
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You will definitely see some slump as the organic material decomposes and settles.
 
Tim Southwell
Posts: 116
Location: Hamilton, MT
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Yes, by all means remove the tree from the bucket before planting.

To reduce the potential for slumping of the planted tree, we placed ~12" long 1-2" diameter sticks in the upright position in the hole. We then filled in with loose soil to fill in between the sticks and build up a platform to place the tree. Though I am certain some settling will occur, I believe it will be minimal. I think you are better off planting a younger tree or one by seed to handle settling concerns rather than say a 100# root ball.

To also promote good growth , we topped the disturbed soil once planted with Sepp's guild mix (clover, lupine, vetch and sea buckthorn.

Lastly, I would recommend charging the wood with water before burying them... say soak them in a tub of water first. Then in year one, don't hesitate to dump a 5 gallon bucket on the plants once in July and and once in August if you find stress in present.

Good luck!
 
Bruce Drukker
Posts: 23
Location: Fallbrook, CA (San Diego County) Zone 10a
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Tim Southwell wrote:Yes, by all means remove the tree from the bucket before planting.

To reduce the potential for slumping of the planted tree, we placed ~12" long 1-2" diameter sticks in the upright position in the hole. We then filled in with loose soil to fill in between the sticks and build up a platform to place the tree. Though I am certain some settling will occur, I believe it will be minimal. I think you are better off planting a younger tree or one by seed to handle settling concerns rather than say a 100# root ball.

To also promote good growth , we topped the disturbed soil once planted with Sepp's guild mix (clover, lupine, vetch and sea buckthorn.

Lastly, I would recommend charging the wood with water before burying them... say soak them in a tub of water first. Then in year one, don't hesitate to dump a 5 gallon bucket on the plants once in July and and once in August if you find stress in present.

Good luck!


Great advice Tim, thanks for taking the time. I feel I've got a pretty good handle on this now. I can't believe how much I've learned already. These forums are truly amazing!

Cheers!
 
I agree. Here's the link: https://richsoil.com/wood-heat.jsp
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