Raised bed around trees

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Old 04-17-06, 03:29 PM
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Raised bed around trees

I finally decided to totally redo a border and I'm implementing a raised bed due to very poor soil and drainage. I got rid of several medium size trees but the wife wants to preserve 2 trees which will be surrounded by the raised bed (about 10" or so).

Obviously I can't just put 10" of soil on top of the tree around the trunk so I made a 4' box around the tree from 2"x12" pressure treated wood. This will keep soil away from the trunk of the tree. My question is what is typically done to make the hole less noticeable?

I believe I have seen the hole filled with large river rock. I could also make a wooden "grate" although my list of projects is getting kind of long as it is. The tree truck diameter is about 10". I believe it's a non-fruiting plum tree as the leaves are dark purple and it's deciduous.


I also wanted ask about the best composition for the raised bed soil. Due to the large volume, I'm primarily using a bulk mix from a rockery that they call "planters mix". I think it's roughly equal parts sand/clay, compost/manure. I'm adding some pure compost and a little manure to further improve drainage and resist compaction. I have read that the only problem with going too rich with the soil mix is that the plants may be more susceptable to root diseases (and of course less water is retained compared to clay soils).

Is there a generally accepted figure for maximum organic content? When I initially got the native soil tested it was 5% but now with the replacement soil it could easily be 50% but this is just a guess.

Thanks
 
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Old 04-17-06, 06:47 PM
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You cannot add more than one inch of soil to the area under the canopy of a tree without running the risk of suffocating the tree, and having it die in the next few years. If you need to raise the soil level 10 inches, remove the trees and plant new ones once you have the grading completed.
 
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Old 04-18-06, 11:07 AM
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Thanks,

Wife came to her senses and agreed to remove trees.

Last year I planted some Lilies within 2' of the tree. They did well but when I dug the bulbs up in the fall I noticed a very dense net of very fine roots very close to the surface. I realized that the roots came from the tree and that it's probably not practical to plant a perennial garden close to a tree anyhow because of competition. My guess is that the tree sensed the nutrient rich soil I had used for the lilies and had sent out fine roots to exploit it.
 
 

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