Drainage for raised bed

[wannabe]

I'm almost finished with the construction of my first 4x8 bed. It sits on concrete and is raised by 2 courses of cinder blocks with a plywood bottom and 2x12 sides. I just need to drill the drainage holes but I'm not sure how many and what size they should be. Any suggestions?
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dispensaries (http://dispensaries.org)

[gardengirl72]

The smaller the wholes the more you should drill. 1/2" to 3/4" should be large enough for the holes. I would put one hole per square foot at the very least.