Snow in Summer (Cerastium tomentosum) has never been a real show-stopper for me. I mean, it performs well, but it is one of those groundcovers that isn't one to stand out. I find that the foliage near the base of the plant can gets brown and mildew-y after blooming.
If you want a groundcover I would suggest Perennial Alyssum. Its proper name (which gardengal mentioned to me) is Aurinia saxatilis. I have seen it used a lot for retaining wall plantings. It has wonderfully bright yellow flowers in spring and silvery foliage that stays nice after the plant blooms. Does wonderfully in dry conditions.

Another idea would be to go with a perennial that will cascade or billow over the side of the wall. I would suggest a pendulous Ornamental Oregano, like 'Kent Beauty'. I have one hanging over a rock edging. I love the flower heads; they are showy even when not in bloom!
Here is a pick of the 'Kent Beauty' Oregano used in this way: picture from dave's garden.

Here is a link that might be useful: cascading oregano

I totally agree with CMK. The cerastium looks pretty good while it's blooming, but I've never been able to keep it from getting ratty later. After a couple of years I seem to end up with little clumps here and there. I pull it out now when I see it show up.

ThinMan

I grow snow in summer in one of my flower beds and it's true that they get brown and crunchy at the end of the summer with no blooms. I also grow soapwort there which seems to stay greener...but we'll see. I haven't gotten many blooms yet. I completely agree with alyssum. It lasts into fall and seems to keep getting better with more blooms. Well into fall when everything else is winding down, the alyssum looks great. I grow that and dusty miller every year.

Maybe it is ok in your climate but over here C tomentosum is a complete thug, impossible to get rid of once it's in your garden. It's basically considered a weed. If they grow in your climate old fashioned pinks would be a good option and a traditional edging in the rose garden. You get silvery pointy foliage, bulging clumps which soften edges and beautifully scented pretty flowers. They'd also go with your colour scheme. You can grow them from seed or just buy a couple of good named plants and take lots of pipings. The only reservation is that maybe if the soil suits hostas and daylilies it might be a bit rich and damp for pinks. But then it is raised bed so drainage should be good.

I have always loved Snow in Summer, and was delighted to find this new garden had some. I remember them from my Mum's garden when I was growing up, and loved the white bell flowers. It is true that they get a little ragged later in the season, but I love it still. I do love that ornamental oregano - it would be borderline hardy here, but i might try anyway!!

Nancy.

Well I let go of the idea of Snow in Summer. How about Rock Soapwort? I can get a pack of seeds for $2.25 from "Diane's Flower Seeds" ( This years garden budget is nearly tapped out)Does Rock Soapwort hold up longer? Kent Beauty is just that but seed is not available and there isn't the funds for plants. I have to reserve $$$ for the cinder blocks and the 8 cubic yards of garden mix. You know the " a $100 hole for a $10 plant "rule. I couldn't do the Alyssum because it is yellow. I will keep an open mind and look some more but in the next 48 hours I need to put in a seed order. Time is running out, we are getting closer to Spring. YEAH! We had snow today, so what. Elizabeth

I have tried unsuccessfully to get it growing on my place here to Oklahoma. The first time I ever saw S-in-S was in Tasha Tudor's garden years ago, and I fell in love with it. It was just so beautiful. She had a silver gazing ball in the center of it and there were evergreens around the growing area that lead back to her shade garden. She had tall blue Cat Mint growing back between the evergreens along the path and some lavender too, I think. There were rock steps and a wide path that wound down and around the circular bed where she grew the Snow-in-the-summer. The gazing ball reflected the whites, blues and greens. It was just gorgeous. I don't know if she had something else in there later in the season, but in May it was breathtaking.

I bought another packet of seed to try again this year. I am determined to have a little patch of it somewhere on this place. If and when it gets weedy looking, I'll just get after it with the weedeater and cut it back. That's what I do with my wild Blue Phlox once it goes to seed.

~ Annie

I like Flora's idea of Pinks, the foliage would look good throughout the year. There's also Arabis and Aubretia they look good spilling over edges. After blooming a light haircut and they'll look decent for the rest of the year.

Annette

Have you considered annual white alyssum? Even here in my cold climate I can seed it and have it grow as a small edging. Great scent also. Probably why I like it is that my parents always had in in a border somewhere.

If purchased as small plants it will spread to a nice edging in your climate. Or seed in situ earlier than I can here. There are other varieties which may be even better.

Here is a link that might be useful: Alyssum maritima procumbens Sweet White

Do you make compost? Perhaps you could save on bought in soil by concocting your own. It is interesting to me to read on these forums how much US gardeners buy in growing media. UK gardeners tend to use what they have and only buy in stuff for seed raising and a bit of enrichment. Wouldn't your native soil work with the addition of compost and maybe some manure?

Maybe I don't appreciate snow in Summer because it's so common here but I'd still go for pinks if I could grow them. By rock soapwort do you mean Saponaria ocymoides? It's certainly pretty and I had some which lasted several years. Another idea is Anthemis punctata supsp. cupaniana. Or how about a dwarf lavender? You'd get the grey pointy foliage plus scent. Again you could grow both of these from seed or buy one or two and grow lots of cuttings.

I grew rock soapwort, saponaria ocymoides, for a couple of years before it completely disappeared. It would probably do better for you in your area. I think our summers are too hot and humid for it. It was spectacular while it lasted.

OK, Flora, your mentioning cuttings of lavender caught my attention! I have failed miserably trying to do that. Could you give me your method, please. This year I am starting again with seeds that are now in the refrigerator chilling as per package instructions. I love lavender but don't grow it well at all in my garden.

Flora, The reason I will be purchasing 8 cubic yards of garden mix is to fill 2 new raised beds. They will be 16 inches high (deep) by 12 by 5 feet. The raised beds will have to be filled first and any left over will be used at the side of the house to expand the bed there. I live in a city and don't have the space or the grounds to generate enough to fill such big raised beds, wish I did. The raised beds will help to extend my years of gardening. Just thinking ahead. Also they will be filled with the Daylilies that I want to breed. No bending over to dab pollen and care for the Mommies. I looked up the Anthemis, nice, maybe a little full. Does it flow over a wall? I love Coreopsis, and it reminded me of it. The Rock Soapwort is Saponaria Ocymoides. I ordered seed today.
Luckygal, I have grown annual sweet Alyssum in every garden since I was a girl, always from seed direct sown. She will do her part again this summer in addition to the Soapwort. The little workhorse of the garden that ties all the unfinished ends together. Elizabeth

I vote for pinks (dianthus), too. Iberis (Candytuft) is a nice edger; evergreen, well-behaved, perennial.

Nell

Hi flora - composting on a large scale is only just catching on in NA. Many of us oldun back to earth types compost, but it was for many years considered fringe, and an enticement to vermin, like rats. Obviously someone was doing it wrong!! Now, at least in Canada, most large centres have composting places and collect 'green' material along with pop cans and newspapers. I think that Token's area gives it away. In Ottawa, it is used for the National Capital Commission's gardens, throughout the City. I've seen a sign in my community about a compost centre, which I need to check out. Even better, nearby, is a Holstein breeding centre that GIVES composted BS away!!!!! Yaaaaa!!! That's my price point. I got a load of it last Spring in my pickup truck, and plan to do the same this Spring, maybe more that once!!!!

Nancy.