posted 11 years ago
I think much confusion can come from oversimplification.
Cedar contains oils that have anti-microbial and anti-fungal properties, which have posed problems in cases where these woods are chipped and applied to the soil in a high surface area situation where these oils can leach out quickly.
I think that if the cedar stays in large chunks, especially with outer bark intact, then the oils will stay pretty much in place. You might see some leave with water exchange, but that would be about it, I think. Which means you have, in a mixed cedar bed, big wooden wicks that will outlast the rest of the wood in your bed and keep the structure that allows them to perform that function that much longer.
Also, cedar mixed in with wood that rots faster will provide structural integrity throughout the bed, so as to maintain void spaces and slow natural compaction due to settlement.
Finally, there is a finite concentration of these oils, whatever the wood we're talking about specifically. Rain washes things away. If the wood is wicking moisture and releasing it, every rainfall dilutes the soil concentration of oils, and more will leach out of the wood, until there's nothing left. My guess is that if you build a hugelbeet even with only allellopathic woods, lets say pine, for now, and then planted it with acid-loving plants, both natives that you'd find in the understory, like blueberries, and a crop of potatoes, which are also acid freaks, but much more tolerant of a higher pH, and any other berries that would handle the conditions, and to guess at a few I would suspect serviceberry, raspberry, blackberry, mulberry, and currant, I would suspect that without the addition or mulching of acidic material, the pH would neutralize, perhaps not within a single season, but relatively quickly to the point of stressing the blueberries.
It might be different with juglone and walnuts, but I think that allellopathy is more of a concern with living plants that are continually producing their chemicals of choice. Otherwise, the rain just washes it away.
-CK
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