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Adding organic matter in tree holes. Yes or no?  RSS feed

 
Andre Lemos
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Location: Castelo Branco, Portugal
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Hi,

i'm going to install a forest garden/food forest next weekend but i have this doubt. When opening the holes for the trees should we add layers of organic matter (straw) in the hole?
I've volunteered a week in a farm to see how they installed their trees and they used straw to improve the poor soil organic matter level. At the time it seemed a great idea but this week i read that it can make the soil anaerobic and by doing that stall the tree growth.

What are your thoughts about this? Add or not? My soil is sandy, with 1.5% of organic matter, with no rain in the summer.

Take care
 
John Elliott
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The reason that straw can do this is because when it gets wet and has the weight of the soil on top of it, it compresses down and doesn't let any air in -- thus it turns anaerobic. This can also happen to cardboard, leaves, anything else that isn't really weight bearing. That is why in hugelkultur we try to use lots of big pieces of wood. They still have structural integrity and air can penetrate through spaces that worms and fungi and other soil critters open up.

It also depends on what kind of soil you have. Clay is the worst, because the small clay particles can block any air passages and prevent any air from getting to the straw. But since you have sandy soil, you should be better off. The rough edges of the sand particles allow more passage of air.

And one of the best amendments is biochar. It has air passages on a microscopic level and also provides a surface for aerobic bacteria and fungi to grow on.
 
Alder Burns
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Location: northern California
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With a very sandy soil your tree sites will probably benefit from some amendments. Fresh, high carbon material (like straw or sawdust) runs the risk of locking up soil nitrogen, whereas high nitrogen matter (like fresh raw manure) runs the risk of "burning" the roots. The ideal is something in between, something aged or composted, or, as stated above, charred. I have often used tree holes as convenient disposal sites for problematical materials like dead animals, uncomposted humanure, and such like, but only by placing these well below or beside the root system of the new plant, such that the roots can grow toward it, and access it at need, but not be forced into contact with it at the outset.
The real problem with amending planting holes comes with a clay soil, such as I have usually dealt with. The process of making the hole results in a pocket of loosened, aerated soil, and adding amendments encourages this and reduces the chances of it settling back to a relatively compacted state. Then, after heavy rain, the air spaces are filled with water and because the surrounding soil is so tight that the water cannot percolate in very fast, the new plant quickly drowns. For clay soils, therefore, planting new trees is recommended into the unamended original soil only, with any amendments being applied later as a mulch or a topdressing, or perhaps in holes beside the root system.....
 
Andre Lemos
Posts: 62
Location: Castelo Branco, Portugal
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John and Alder, thank you for your oppinion and explanation. I understand the point now and will try the biochar or maybe even decomposed manure.
 
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