A Gardeners Forum Forums Gardening Reference Gardening in 2004 Flower bed over asphalt?

I'm not sure how to describe this.

I have a long asphalt driveway leading up to my house, ending in a retaining wall about 5 feet high, steps off to the side leading up to the back door, and the garage on the left.

I've thought how pretty it would look to make a flower bed at the foot of the retaining wall (end of the driveway) running the length of the retaining wall (about 20 feet).

Here are my questions. I don't have the time, equipment or money to dig up the asphalt where I want the flower bed. Can I just build a long flower bed, about 2 - 3 feet wide, directly over the asphalt? How deep would I have to make it, to compensate for building it directly over the asphalt? What would be best to build it with?

I envision the flower bed at the foot of the rock retaining wall, colorful flowers and plants in it, maybe a climbing hydrangea or other climbers snaking up the wall, and creeping phlox and other trailing plants planted at the top of the retaining wall trailing down towards the flower bed. It looks lovely in my head
but I don't know how do-able, or practical my plan actually is.

Am I ?

Ronni

Dear Ronni,

I don't see why you couldn't, provided that you built in a drainage system. Perhaps if you filled the bottom with four or five inches of gravel, so excess water could have a place to go. Or maybe you could use those bricks with holes in them along the bottom?

This would be if you built a retaining wall at least a foot high, to contain your soil.

Bess,

See, I KNEW I'd get sensible answers if I asked questions! I hadn't even THOUGHT of the drainage question!

I envision the bed to be at least a foot high, perhaps a little higher. "Bricks with holes in them along the bottom?" Do you mean put bricks in the bottom of the bed, where the gravel would be? Or build the bed with bricks, make the bed walls of brick, and let the holes be natural drainage?

Hope my questions are clear!

Ronni

I recommend at least 18 inches depth. I'd also punch holes in the asphalt for drainage, or put drainage holes in the bottom of the wall. Also keep in mind that a raised bed like that needs lots of watering. Use a high quality mineral soil, not potting soil. Potting soil is mostly compost-like material that will drain too quickly and decompose and sink.