Raised beds over concrete or asphalt?
By Canadianakid
southern Ontario,
Canada 
I'm planning on installing raised beds overtop a concrete and asphalt pad on my property. I'm concerned about:
1) lack of worm activity for aeration
2) drainage
3) type of barrier to use between the soil in the bed and the asphalt/concrete base
4) minimum depth of beds required for certain plants (tomatoes, for example)
5) Any other insights about this arrangement your experience has taught you!
Your insights will be greatly appreciated!
28 May, 2009
Answers
You must remove all the asphalt, also I would remove the concrete, chemicals from both will harm growth and are toxic, polluting anything you grow. A membrane between earth and concrete/asphalt would not be enough, worms would not live in the area. You would have bad drainage or it would dry out leaving it useless for growing. 9 inches is the minimum depth of soil. Tomatoes could be grown on a ring culture method. If you need any more information please come back.
28 May, 2009
I wouldn't do it, not without punching holes through the pad for drainage with a kangadrill.
28 May, 2009