How about blue pimpernel? It's a bit of a wanderer, but short.

Also, Kalimeris incisa 'Blue Star'. It forms a tidy mound and is long blooming.

http://images.google.com/images?hl=en&q=Kalimeris%20incisa%20blue%20star%20&um=1&ie=UTF-8&sa=N&tab=wi

Some of the verbenas may also work for you.

Ajuga blooms in spring but has nice foliage the rest of the year. (Mine is evergreen)

Here is a link that might be useful: anagallis monellii

Thanks, organicmickie!

Does anyone else have any suggestions?

"Starry Eyes" Nierembergia bloomed all summer long for me. It stayed pretty low. The blooms were so pretty.

For the situation you describe, I might go for annuals such as blue or blue-purple petunias. I know, I know, this is a perennial forum, and I grow very, very few annuals myself. However, there are times when they are worth their yearly cost, especially when you want prolonged flowering in a restricted space. If there are any good nurseries near you, take a trip in the early spring and check out the annuals in flats, ask for recommendations and see what you like. Even if you want to try perennials next year, that will give you more time to research plant material.

what is the sun variable

if full shade.. blue or blue variegated hosta might give all summer long interest ...

ken

Early morning sun for a few hours, then the shade of a tall flowering cherry tree until mid-day, and building shade thereafter. They'll be exposed to open air to their north and northwest, but they won't get direct sun because my townhouse blocks the sun.

Bluestone Perennials sells a "hardy ageratum" that's actually a cultivar of Eupatorium coelestinum. Does anyone have any experience with this? Bluestone's catalog indicates it can spread. How aggressively does it do so?

(Hostas will work well, but I'd rather go with something else.)

I have Eupatorium coelestinum 'Wayside'. In my zone 4 garden it has spread to make a nice clump and so far at least is not aggressive. This will be it's 4 year in the ground. However, since it's borderline hardy here, it may act differently for you. Please note though, it does not begin to bloom till late August or even early Sept. for me.

Thank you hostaholic2!

I'm delighted to receive any and all advice because I'm unaccustomed to gardening in damp areas, yet know there are some notoriously aggressive spreaders that love damp areas.

How about Brunnera? It has small Forget-Me-Not like flowers that bloom in the spring. The foliage is attractive, especially on the variegated cultivars. The plant gets a little over a foot tall and is a clumper.
Corydalis elata (and other cultivars) is a blue flowering groundcover. Very long bloomer with tubular shaped flowers. Corydalis reseed VERY well, but they are so easy to pull up that I wouldn't consider them invasive.
There are many Perennial Creeping Geraniums that are short. Omphalodes (Blue Eyed Mary) is also nice.
CMK

I had two Rozanne geraniums that rotted out after two years. :-(

I have thought of both Brunnera and Corydalis, so your info. on what they are like is welcome!

Another possibility is plumbago.

I can't think of anything blue and relatively short that lives in the swamp.

Suggestion: Offer to be the new maintenance person in charge of watering & landscaping...

Forget me not, Myosotis sylvatica ÂVictoria Blue has a fairly long bloom time and does very well in wet environments.

Sounds like moist, partial shady conditions......
Brunnera 'jack frost'
flowers for short time, but nice foliage
{{gwi:196462}}
heuchera 'purple petticoats'
one of the few heuchera's that bloom all summer for me
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dicentra exima (bleeding heart)
blooms most of the season as well
{{gwi:196464}}
polemonium 'brise d'anjou'
short bloom time, but nice foliage
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ajuga multicolor
does spread some, but is pretty year round
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Have you considered ferns or grasses? Lots of variegated forms out now that like shadier conditions.
Sometimes instead of trying to get flower power for the full season, I go with foliage color as a substitute...best of all you don't have to keep cutting them off to keep up color.
Good luck and show us a pic of your final decision. This is what I love about gardening....decisions...decisions...
flora2b