For Jim or anyone who might be able to help, my little garden is bordered by a couple of large oak trees within the reach of tree roots that extend 50' or more from the base of the trees. The roots find their way into my conventional raised planting beds. I've been forced to dig out the dirt to a depth of 12" - 18" below the level of my raised beds and lined the beds with a 4 mil plastic barrier. In effect, each bed is a large 3'x6' planting pot with no drainage. Total depth of the beds is approx 18" - 24" deep. The depth of the beds is deep enough that even heavy Florida rains do not turn the beds into swimming pools.
However, I am concerned that if I try to use the Mittleider gardening method, I will need to "shallow up" my beds, rather than try to adapt them. I suspect that 'salt build-up' in the current beds will negate the benefits of the Mittleider method.
Even if I start from scratch and create above ground grow boxes, I will still need to have some kind of barrier to prevent the tree roots from invading. (Don't even suggest that I cut down the trees. My wife is meaner than a junkyard dog!)
Tell me if this idea is worthwhile. How about if I lay down a plastic barrier at ground level, and then construct grow boxes twice as high as normal, say 15" high. Then lay the grow boxes right on top of the plastic barrier, fill the bottom of the boxes with several inches of heavy soil, and then overlay with the lighter sand & sawdust. Excess moisture could drain out where the box meets the barrier, and I could avoid salt build up, and at the same time keep the tree roots out.
Any better ideas out there?
Tree root problems Jim Kennard et. al.
blmlb,
We have a very large oak tree only a few feet from the north end of our garden, and so far I haven't found any feeder roots from it in the garden. I just tilled the garden to a depth of 14 inches as part of our fall cleanup, and encountered no tree roots. I suppose there many varieties of oaks, but in my experience they don't have what you would call "invasive roots".
"In effect, each bed is a large 3'x6' planting pot with no drainage."
You definitely don't want that. Drainage is very important. Digging out the tree roots every year would be preferable. Here in Maine we get quite a bit of rain. It rains every few days. So our oak trees are not tempted by the garden. They have plenty of other space in which to feed. You might try watering and feeding your oaks. Then maybe they won't be so tempted by your raised beds.
MM