presley wrote:
Well, I pretty much have to disagree with everything Warren wrote below,
since I have had a raised bed for vegetables over an old asphalt driveway
for 4 years, growing radishes, lettuces, chard, sugar peas, tomatoes,
collard greens, parsnips and chinese cabbage. My raised bed is about 12-14
inches high and about 5 by 10. I used old concrete/aggregate that was
sawed up from an old patio into neat rectangles as the sides of the bed.
One side of it is bounded by an old loose stone retaining wall. I filled
the bed with various bags of potting soil, top soil, dirt from other parts
of my garden, chicken manure, steer manure, etc. I add a bag or two of
manure every year to the top of it. My driveway is at the top of a gentle
slope. Drainage has never been any kind of an issue. (Well, the blocks
that make up the sides are not tight together. Soil doesn't leak through
in any quantity, but I suppose if I overwatered, the excess would come
through the openings between the blocks). When I pull up plants at the end
of the season, they have not put down roots into the asphalt. The average
root depth for most of the vegetable crops is about 8-10 inches. A
neighbor's maple tree hangs over the bed from the north side of it, so it
rarely gets rained on. I have to use a sprinkler on it, but that is not
unusual in my climate.


You may be comfortable eating vegetables grown over petroleum products, but
that doesn't make it a good idea. You're also going to have an interesting
surprise when you remove the bed, and examine the condition of the asphalt.
After 4 years of being covered by soil, that asphalt will be in a very
different condition than the surrounding driveway.

--
Warren H.

==========
Disclaimer: My views reflect those of myself, and not my
employer, my friends, nor (as she often tells me) my wife.
Any resemblance to the views of anybody living or dead is
coincidental. No animals were hurt in the writing of this
response -- unless you count my dog who desperately wants
to go outside now.
What's on TV? See the new fall network schedules online:
http://www.holzemville.com/mall/tele.../fall2005.html