While it's not really a cascading plant, might vinca minor (periwinkle) be an option? Or how about planting a whole bunch of strawberry plants-- their runners will quickly fill in any gaps you have (and you eventually get something to eat as reward for all your hard work..)

Aubrieta? And there's another one with a similar name which is escaping me at the moment that looks pretty much identical. Both of them cascade beautifully. Sweet alyssum cascades and reseeds (everywhere ).

I love the saponaria (but I love phlox subulata, too). What about snow-in-summer (cerastium tomentosum) or sweet woodruff (galium odoratum)?

Kinnikinnick is nifty. What about bunchberry (cornus canadensis)?

Oh my, I somehow missed Aubrieta... that's gorgeous. I just added it to my list. I like the bunchberry, too.

Another question regarding the wall... how do I decide where to plant, and how many varieties of plant? Do I stick to one or two, or can I use 3? Intermingled, or grouped by plant?

I have a similar west-facing wall, but some of it is in light shade and it is along the back fence of my back yard.

A few years ago I planted a mix of sapanaria, cerastium tomentosum, and aubrieta. There are some of the native bleeding hearts creeping in under the fence, which is a nice unplanned addition.

Pros: It looked fabulous in bloom, with the pink, white and purple flowers all at the same time, and the snow-in-summer has nice, contrasting silver foliage. All the plants needed to be cut back at the same time, so that was easy to do.

Cons: The snow-in-summer self-seeded and spread and looks ratty much of the year. The saponaria is also a self-seeder, but it's easier to cut off the seed heads. Overall, there was not enough textural contrast because all the leaves except the bleeding hearts are about the same size. The whole thing looks bad after I cut them back, around this time of year, but that's really OK because it sorta recedes into the background and other things in front fill in and look good.

I recently took out the snow in summer and replaced it with deutzia gracilis 'Nikko' and I am thinking that will work well. I am hopiong for at least some fall color from them too. I am looking for something else with bigger, colored or spikey foliage to add to the mix. At one time I had some bearded iris there too, but their roots were too shaded by the other plants and they didn't bloom, so I took them out.

I am very happy with the saponaria. It grew like crazy the first year, from 4" pots to about 3 feet wide and blooms for about 6 weeks. Since I cut it back so severely, it hasn't gotten any bigger. I stopped watering it midway through the first summer and never have since, so it is definitely drought tolerant. The only negative is the copius seed heads frighten me and I hate to think what would happen if some year I don't cut it back in time and all those seeds are let loose in my garden. The little self-seeding that it has done has been manageable, though, and people have been happy to take them as hand-outs. I don't understand why this plant is not grown more in our area because it's a winner with me.

I have cornus canadensis in another spot and I love it, but I don't think it would do well with western sun, or it would need a ton of water.

I appreciate your input, Karchita. I'm thinking snow-in-summer is off the list. I want the plants to be relatively easy to care for and not too messy when not in bloom. Sapanaria doesn't sound too difficult... maybe worth it for the fabulous results? It sure looks gorgeous in pictures. What was your experience with the aubrieta?

I've never run across deutzia gracilis 'Nikko', so I googled the image and it looks very pretty. I'd be interested in knowing how yours does.

Do you have any photos of your wall? I'd love to see how you placed the plants.

Sorry, no photos. I recently got a digital camera but the blooms are all gone and everything is hacked back. It really is at its worst right now. Maybe next year.

I think how many types of plants to have is really a matter of taste. Some people like to have a large sweep of one plant, but I prefer mixes. Plus I like too many plants to settle for just one or two. It looks like you have a lot of space, so it seems to me that you could have six or seven types of plants there and it wouldn't be too busy. Depends on what you like.

I often will group plants in threes when I plant them, but the saponaria got so big, I only needed one to make a nice big patch. (I did a trial of just one for a year before I bought more for the whole length of wall). Same with the deutzia, which apparently can get to 6 feet. It all depends on scale. If I have a big space and small plant, I group them, but didn't need to in this case.

I placed them by just eye-balling nice spaces between, not measuring, so it would be informal. I repeated enough that the effect is rhythmic. I placed the saponaria first about equal distance apart and then filled in between with the others. Hard to describe, but remember you can always rearrange later if you aren't happy.

The aubrieta has been easy to grow, but slow.

Someome suggested galium odoratum, but that stuff really spreads and is hard to get rid of.

Other ideas for you are arabis (rockcress) and iberis sempervirens. Maybe some sedums would work for you, too, or grasses or daylilies for some vertical interest.

Neither bunchberry or sweet woodruff will be very happy along a west facing retaining wall and neither has a very cascading habit anyway. A couple of other choices would be trailing rosemary or sunroses (Helianthemums) - I don't believe either are very appetizing to deer, they are evergreen and offer a different season of interest than do the more common spring blooming rockery plants. And there are many hardy geraniums that would fit the bill also.

We have a wall facing sort of sw and it is planted with purple aubretia, yellow perennial alyssum and white arabis. It looks fabulous for a couple of months in the spring and respectable the rest of the year. It would look wonderful against the grey stone.

Many (most) of the plants suggested are likely to fail on damp, heavy soil. Lysimachia nummularia might work out, if you like how it looks. Do plant an assortment of things, for the sake of visual interest, as well as not having all your eggs in one basket, in case a problem appears with one of the choices made.

Thanks for your help, all. I've added to my notes and I'm off to do more research. Ron, yes, absolutely the clay is hideous stuff. When wet it's just a big glop and when dry it's hardpan. They could make bowling balls out of this stuff. What I've been attempting to do is to plant above the surface of the clay. I've been breaking up the clay under each plant, mixing in a good hefty dose of compost and sometimes peat moss, and then planting almost completely above grade by filling in soil around everything. It's a pain and it's expensive, but I really want to make this yard work. I hope I'm on the right path.

Can anyone identify this cascading plant from a distance? I drive by it regularly and it's spectacular. Today I took a photo, but this is as close up as I could get. Thanks.
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Looks like lobelia. A business not far from me has been in a large wall/waterfall feature and has this planted in mass all over it. Especially earlier in the season it looked spectacular. Its fading a bit now, but still looks good.

One suggestion, I have some lemon thyme in my yard that has grown very quickly and has "cascaded" itself over a large rock to the point I can't see it. It has a variegated with a bit of yellow in it and the flowers are a soft pinkis purple. Not really what you would call show stopping, but if you needed a lighter color in there it might make an interesting addition.

Does lobelia come in dark purple? I've seen all shades of blue, but I haven't seen purple.

Funny you should mention lemon thyme... I was admiring some in my neighbor's backyard last night.

Save yourself a counterproductive step and just plant in the lighter soil on top, leave out the amending underneath.

Here is a link that might be useful: The Myth of Soil Amendments

I think lobelia can come in a dark purple or even pink shade, but not sure. Although its very common here in the PNW it's new to me since we don't grow much (or any of it) in Louisiana where I am from.

As far as the lemon thyme goes, if her plant is well established, you should be able to get some rooted pieces off of it without disturbing or even changing the look of the mother plant. I just kind of reach underneath the plant and pull out a chunk! Very scientific I know :-).

Another blue flowered cascading plant is Lithodora- if the link doesn't work just google an image. I don't water mine much so I'm assuming it is drought tolerant.

I'm wondering if a cascading type of rose or short type of clematis might work as a focal point. Perhaps a vining plant like Holboellia might work, too, or a cascading form of fuchsia. Of the ground covers mentioned above, Kinnickinnick has the best year-round look in my opinion, and one form has pink flowers.

Here is a link that might be useful: Lithodora

I love Ajuga, comes in several color variations, low growing and has a short flower. Creeping phol is nice, mine gets about 8 inches tall but not so much as trailing as clumping. Thymes are nice with the added bonus that deer don't like herbs. Very nice ones to choose from. Knickknick is nice - more shrubby looking but a nice trailing dark green plant. Trailing Oregano is very nice but hard to find. Mosses are great, Snow in summer cascades nicely also. Have fun..

I've had great luck with a couple of creeping thymes (vs the clumping type), sedums, and a rosemary that is a draper, all weaving throughout a short boulder retaining wall. Harder for me is a stacked paver wall with the pavers wide - 8" or so. I want plants to cross the 8" and hang down the 4ft wall and once the plants hit the heat of that concrete, they decide its not such a good idea to proceed. I finally got 2 clematis to drape down but they really don't want to, they want to climb (unless you WANT them to climb, then they fall down.) My aubretia disappears for most of the summer.

I grow tunica (petrorhagia) on the top of stone wall, but in an area that is slightly shaded. I also have it in a hot sunny garden. It's got GREAT texture, blooms for a long time, and is trouble free. It drops an occasional seedling, which I love. On the wall, it does cascade.

In the sunny area of the wall I've got snow in summer, but I'm planning to replace it with gypsophilia repens, which is MUCH better behaved and has similar silvery foliage.

Love my saponaria - great foliage that would contrast well with tunica, as it's robust looking.

Did I miss something, of did you not tell us how long the wall is? The number of varieties you want to use would depend on this.

Anyone know where I can get seeds for purple Aubrieta or would be willing to do a plant or seed trade??? Please help!!! Trade list not yet updated this year.

Gardenbud

amazon.com, ebay.com, myfolia.com, etc offers the availability of purchasing Aubrieta seeds and plants which differs their prices according to the species and their types.

Here is a link that might be useful: Aubrieta

A plant I love for rock walls, but is underutilized, is helianthemum (sun rose), and it comes in yellow, orange, red, pink and white. If you are considering lithodora, make sure you plant the crown high. If you plant it with the crown at or below grade, the leaves in middle of the plant will turn black and drop off, leaving the middle of the plant bare.

A plant I love for rock walls, but is underutilized, is helianthemum (sun rose), and it comes in yellow, orange, red, pink and white. If you are considering lithodora, make sure you plant the crown high. If you plant it with the crown at or below grade, the leaves in middle of the plant will turn black and drop off, leaving the middle of the plant bare.