Al Senner wrote:Ive read that 8 in. diameter is the max size for fruiting on logs but whats the minimum size?
Where did you read that??? I personally wouldn't bother to inoculate logs of less than 20 cm (8in) diameter. Only oak inoculated with shiitake works well with smaller diameters. I've had success with oyster mushrooms on hazel and beech with only 4-5in, but the yield wasn't worth the effort.
Usually I use maple and beech from 10-20in
I've seen monstrously big crops of oysters growing on fallen beech trees around here. I think one fallen tree had over 100kg of fruiting bodies on it. That one had a trunk over 3ft thick. You can definitely get useful crops from large diameter wood.
The three things I can think of that might come in to play are:
Ease of handling - smaller diameter pieces are easier to work with so might make commercial work more efficient.
Smaller diameter logs have a different ratio of heartwood to outer new wood - the outerwood contains more readily available sugars so is more rapidly consumed by the fungi. Smaller diameter wood might therefore be more productive than lareg diameter, but that would by no means mean discarding larger diameter material.
Larger diameter material might have more value put to other uses (firewood, planking etc...)
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Although Michael's other reasons are good too, the main reason I've seen from professionsals is reason number two: because the ration of new wood to heartwood is better, so there are more sugars upon which the mycelium can grow. Yes, I've typically seen 4 to 8 inches as optimal, but if it's your own lot, and you're cutting your own wood for free, that changes the financial and logistic dynamics.