Thanks for all the input! Unfortunately, the source of the seeds probably come by the birds and groundsquirrels which are everywhere, and just behind where I stood to take that picture is the woods we live on the edge of...where I'm sure lots of seeds stray from. I'm not at all opposed to using round up! If I use the stuff, how soon after can I try to plant something within the cracks? I found some creeping phlox on sale and bought some. I love it...cascading down other peoples' walls...may take awhile, but I'd love to have that effect myself. I am not sure if the ground squirrels will mess with any plantings....our yard is overrun with them (rock walls especially), but I'd like to try. Thank you for all the suggestions! I am going to read them all more thoroughly and take some notes. I saw a rock wall belonging to a neighbor of a friend of mine on Thursday. They have phlox on the top of theirs...it actually grows into my neighbors yard. Perhaps that might even keep the weeds off the top of the rock walls as well? To the person who suggested inserting smaller rocks in the larger spaces...I've actually started doing that, on another wall, the largest on our property. If interested, I have a photo album that contains pictures of most of our yard...and I believe all but one of the rock walls... you can see them on the link below. yes, I know my whole yard needs a lot of work. Some of you have seen some of these photos before. Here is a link that might be useful: yard album

Thank you for your reply, I apologize for my delay in responding. I just finished this area and it was a massive 4 week project. I ended up digging a wedge shaped hole 2 - 3 feet deep, 6' wide at the point and maybe 15' wide at the bottom. I filled this with the gravel/soil mixture, then brought in 5 yards of topsoil to fill two planters and cover the other areas. This was combined with roughly 1200 lbs of cow manure compost. In the spring we will continue with planting. This new gravel "wedge" is a low point in the yard and testing drainage with a garden hose it seemed to work well.

daisyinga -- Paper bags! Duh...why didn't I think of that? That makes SO much sense! I am so glad I posted about this. I will DEFINITELY try that suggestion. Not to mention I still have a few rolls of that contractor-grade brown paper (y'know, the stuff they put down to walk on in your house, while they're doing finish work, so they don't scratch your floors) leftover from the renovation. That would be good too, it sounds like; and so easy to roll out! jmzms -- Thanks! :) I hope they do. Since I posted this and have gotten so many responses, I am starting to wonder if maybe the neighbors are, indeed, more "curious" than "disapproving" when they are doing the drive-bys. foxesearth -- I don't want it to be a big pile of rock...and I don't want it to be a southwest garden...I guess I don't really have any pictures (except in my mind) of how I want it to look. I guess I sort of jumped into it, when hubby and I finally decided that's what we wanted out there. At first, we just wanted something to not make the culvert look so...culvert-y...and also to keep the soil from eroding down into it. The rock garden idea sort of evolved from there. BTW, the pix I posted show more of the flagstone in the actual culvert part, and some of those are being removed in favor of more Tennessee Field Stone (the rock used throughout). There will probably still be some of the flag stone left (because it matches the path I'm building down through my foundation plantings), but it will be only in just the bottom of the culvert.

treebarb, I've been in love with Abies concolor for decades; have never owned one. I'll go peek at Lowe's. We haven't made a decision yet, family stuff in Florida happened and we just returned home. Do you think the shallow roots would be a problem? We don't want it falling over in the wind and hitting the house (but of course on a 3-foot Lowe's tree we'd not have to worry about that for a while)! The neighbor's trees are not any wind protection. One is at the very front of her house and the other smaller juniper is between our houses. The prevailing winds are straight up the slope much of the time, so whoever's out back is going to have to withstand 50+ up to highest measured at 76 mph. Doesn't happen all the time, of course, but I'd say 20% of the year at least. I just looked up Bosnian pine: "tolerant of severe wind exposure". I like its looks online, and it sounds like the ticket to me. Thanks for your helpfulness. I very much appreciate it.