I'd check into Salvia patens or Salvia guarantica (sp? I was too lazy to look it up). Both have varieties with pale blue or cobalt blue flowers.

For a lower grower, check out Salvia daghestanica or Salvia jurisicii 'Blue'

There are also true blue penstemons that are similar in appearance to salvias. Consider Penstemon virens or Penstemon cyananthus.

All of these plants will require good drainage, of course.

One of the Salvia nemorosa/Salvia x superba varieties would probably fit the bill, such as "Marcus" or "May Night" (which is more of a blue-purple). Salvia transylvanica is another useful Salvia for the perennial border.

I would definitely consider using temperennial Salvias like the S. patens or S. guaranitica that bindersbee mentioned (they might be hardy in your area if in a well-drained spot and mulched for winter protection). S. guaranitica would get taller than the 18 inches you mentioned for height, but also is a prime attractor of hummingbirds.

I like salvia ChiQuita and S. Faenecea. I don't know their hardiness and if they will do for you. I also like Salvia Azure var grandiflourous. I can't do a lot of Savias from Europe because of my soul and heat. The Balkan salvias are very nice. S. Nemerousa Too . Meadow sage, May's Night. I would grow them in a heart beat if I could but I can only drool from afar.

I adore blue salvias. I have tried several over the years here in east central MS. I am on the border of zone 7 and 8, so my climate is hotter than yours, but still, you should be able to use some of this information.

Salvia guaranitica, Black and Blue, is excellent. It is dead hardy for ME, and spreads enough to supply new plants every year. It gets about 2.5 feet high, begins blooming in mid summer, and goes till killing frost. The blooms are really, truly, deep blue.

Salvia Indigo Spires is taller than Black and Blue, but the bloom spikes are larger and showier. Its blooms are a deep navy blue. The plant gets about 4 to 5 feet tall and wide. It's somewhat rangy, and not absolutely hardy for me, but I grew it for years due to its showiness. Three years ago, I discovered one of its "children":

Mystic Spires. This is a wonderful Salvia, perhaps my favorite. It gets about 2 feet high, has a very neat, upright form, with deep blue blooms that never stop. I Just set out some cuttings I kept over winter in my garden. They are already blooming and will go until killing frost. As far as winter hardiness goes, I will typically only have about 1/3 of my plants make it through our winter. I don't know if they dislike our winter wet (very possible) or if the cold gets them. Either way, I don't risk losing them all, as they are very difficult to find in my area. I take cuttings in late summer, stick them in potting soil on my deck and water them daily for about 10 days. That's all it takes to get them rooted. I grow them under lights in my basement through winter. Rarely lose more than one plant during this time.

Salvia farinacea, "Victoria" or "Rhea". Farinacea is the other parent of Mystic Spires. Mystic gets its larger size from Indigo spires, but it's long bloom season and neat habit from farinacea. These farinaceas get about 12 to 18 inches high and about 12 inches wide. They are neat, bushy plants that make blue spikes from spring to killing frost. They used to be very easy to buy in the spring as annual bedding plants, but they have gotten scarce the last two years. So, I have begun starting them from seed. I got "evolution" from Parks this year and had a very high rate of germination. They should be ready to go out into the ground in another week or two. (They are also easy to start from cuttings.) Last year, for the very first time in 15 years or more of growing this plant, my plants were just eaten up with mildew by fall. Every cutting I took in the fall failed. But, since the seeds are so easy to start, I will probably go the seed route from now on.

My growing season is so long that I cut my farinaceas back (Mystics too) by about a third and fertilize them well in mid July. They recover quickly and will bloom continually without flopping until frost in November.

Salvia leucantha is a lovely late summer bloomer. It has grey green foliage and lavender/purple fuzzy blooms. It gets about 3 to 4 feet high and wide. It looks very fresh in the fall and complements all the yellows and oranges of that season. It is completely winter hardy for me.

Salvia chaemydroides is a beautiful (really beautiful) vivid blue, low (12") bloomer, but it doesn't seem to like my very moist, heavy soil. It's actually said to be almost too vigorous in other parts of the country. The blue coloration of its blooms makes it well worth a try anywhere. I am on my second try to make it happy, and will try again in another place before I admit defeat.

Salvia lyrata (Purple "tornado? volcano?"): I grew this one from seed and I LOVE it. Not for the blooms, however. The foliage is a vivid red-purple and it holds that intense color all summer long, even in my full sun. It is a great edger. I remove the white flowering stems.

I have also grown (and discarded)
Aztec Skies (extremely invasive, blooms not showy, plant messy)
I had read that salvia nemerosas don't like the south. My experience agrees:
Caradonna: although it's supposed to be the best nemerosa bet for the south, it was a complete waste of money for ME. Never grew. Did not survive my winter. Probably hated my extreme heat and humidity, not to mention my winter wet. In your area, I'd sure give it a try, because it's a stunner when it's happy.
May Night: certainly better than Caradonna, but not that much. Its season of bloom is too short (about a month, max) when I can grow farinacea so easily.
Purple Rain: Lovely plant in the garden center, but the grey/purple color of the blooms didn't show well at all from a distance of more than 3 feet. The plant is floppy. And, it didn't survive my winter. I won't replace it.

So, that's my salvia experience. I hope this helps you or someone else. Good luck! Let us know what you try and how it works out. (Especially if it's something I haven't tried! :)

Since I've seen that some of these beautiful blue salvias are not hardy in my zone, could I grow them as annuals? Would they bloom the same year if I grew them from seed? I had Black And Blue Salvia given to me by a friend and it didn't live through the winter here. It's a lovely plant, and I was wondering if I could just plant seeds in the spring get summer and fall bloom here.

Linda

You can dig up the tubers of Salvia guaranitica and overwinter them in a pot in your garage and then replant the following spring. Just keep the soil containing the tubers barely moist to keep them hydrated but not too wet or they could rot. Friends in Michigan have been doing this since I recommened it to them several winters ago.

Salvia nemerosa 'Blue Hill' does very well for me, similar to 'May night' or 'East Friesland' but much blue-er. Bulgarian salvia, (see below) S. forskaohlei, is classified as violet blue and is long-blooming and trouble free.

Here is a link that might be useful: salvia forskaohlei

Although not a perennial (and I'm in Z5), I love to grow Mealy Cup Sage each year (um...Salvia Farinacea I think). It's the right height, and never fails to perform in my garden. The spires are almost neon here.

Ahhhhh . . . a rainy day, a hot cup of tea, and replies to my post at Gardenweb. What could be better.

It's going to be tough deciding between East Friesland and Carradonna. Carradonna has those beautiful purple stems. But nemorosa Lubeca blooms three weeks longer than East Friesland!

There's a Salvia called 'Marcus' at Bluestone Perennials that grows 12" high and said to be a short 'May Night', hummm. But then the 'Blue Hill' Salvia at Bluestone is a beautiful SKY BLUE color! I tell ya, this ain't gonna be easy . . .

I printed out your replies and will search again for some I couldn't find. Thanks. I'll post back and let you know what I decided.

linlilly, salvias are very easy to start from cuttings. Take them from healthy plants in late summer, get them rooted, and you can take them inside for the winter if you can provide light. Mine do well under just flourescents, which makes sense since most do well in afternoon shade.

It should be mentioned that some Salvias are temperamental about growing indoors from cuttings. They'll root, but S. guaranitica tends to deteriorate markedly over the course of a long winter indoors for me under lights. Same for S. leucantha. For a long season of bloom, these may be best when bought as good-sized plants in spring and treated as annuals where they are not reliably hardy (in a protected spot, S. guaranitica can make it though a zone 6 winter if well-mulched).

Black and Blue -- I saw somebody mentioned earlier up in the thread. Is it possible to grow this from seed? Will it bloom in same season? I am in zone 6 where the plants don't seem to overwinter unless someone can tell me of special treatment. Cats and general family untidiness make it unlikely a tray of plants will last the winter in my house, so I'm looking for ways to do it all outdoors.