Growing Plants Out of a Wall

[jbelak]

I want to grow some kind of covering plant out of a very tall, large retaining wall. The wall is a north facing wall in my backyard, however most of the sun it does get it blocked by my house during certain hours of the day. Every year I have to spray the wall with a weed killer and then pull out all the dead weeds that grow in the cracks. This works and lasts for about 6-8 months. As soon as spring starts to warm the temp, the weeds come back. The first year when I started the garden it was not so bad, but now the run off seems to harm the clematis vines that thrive on a trellis that leans against the wall. I want a seed or plant that will grow in the cracks of the stone wall, fend off the weeds and not do too much damage to the exterior and strength of the retaining wall. My neighbors yard has a very dark green, large leaf ivy growing but it seems to take over the entire wall. I'm a bit skeptical that it may damage the wall itself if I decide on an ivy. I'm attaching a few pictures of my backyard. Please help.