Currently blooming in my perennial beds are balloon flower, black snakeroot, garden phlox, gayfeather.

I love the color contrast that Palace Purple heuchera/coral bells offer along with Veronica. I have double blue balloon flowers, double white balloon flowers, phlox 'David' (which blooms white) along with several varieties of pink perennial phlox. Sedum 'Black Jack' offers a contrast in colors with deep purple foliage.

Caryopteris/blue mist shrub is an airy plant but attracts pollinators--it's a fragrant late season bloomer.

My winter sown butterfly bushes are just beginning to bloom & Hibiscus syriacus/rose of Sharon is blooming at the moment along with some late-blooming daylilies.

Hydrangea is blooming for me now in Zone 6a plus I see many other cultivars blooming around the area altho' many would likely exceed your height requirements.

Take the guesswork out of the equation and buy/check out of the library a perennials book that will guide you in choosing plants that meet your requirements.

Wishing you success & best of luck!

Best thing to do is always to drive around and see what's blooming in your area when you have gaps. Not sure where you are, but in my area it seems everything is in bloom right now. Agastaches are all looking particularly stunning these days.

I don't know where you're located, but when I lived in the Midwest, my favorite combination for late summer - fall was Aster Frikartii Moench with Coreopsis Moonbeam, Boltonia Snowbank, and Chrysanthemum Emperor of China. The colors carry well in the cooler weather and you'll have elegant flowers until the first freeze. That happened in October where I lived.

Cheryl

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This post was edited by GreatPlains1 on Wed, Sep 4, 13 at 5:18

Thank you so much for the suggestions.
On the black snakeroot, can they tolerate part sun? and if so, which of the dark varieties do you like??

You can check my old August thread for inspiration. I'm relatively high up North, so I may be delayed in comparison to others.

Here is a link that might be useful: August jewelry

My favorites for the time before the asters and the monkshood are cardinal flower and black eyed susan. I like the the red and yellow color combination and the long bloom time.

nancy0903 - Cimicifuga racemosa/black snakeroot/bugbane/cohosh will tolerate full shade as well as part sun (in moist soil). I'm currently growing what I believe is Hillside Black Beauty altho' my notes don't specifically identify the cultivar I bought & planted several years ago. I love the plants and so do the bees--once the flower plumes form, they're on it constantly, sort of like kids jumping up and down on a mattress.

penstemons and phlox are doing well, as is the verbena bonariensis. Indigofera is getting ready to flower, as is gaura, various agapanthus and achilleas. Dierama is still blooming and there will be various gladioli to come. Crocosmia yet to flower much (look well with eryngiums),
Waiting for perovskia, althea cannabina, schizostylus, plumbago, anemones, libertia, rhodochiton, watsonias, miscanthus and panicum grasses, The roses are ramping up to the next flush (I only usually get 2 good flushes a season).....but in truth, its all about the fruit and vegetables at this time of year.

There you have it, advice straight from England!
You could cheat a bit and put in a few dahlias. I think they would fit well into an English style border.

Hmmm...

Zinnia, even though they're annuals they tend to self seed.

Butterfly Bushes, mine are all calling hummers and butterflies by the hordes.

Agastache as well as bee balm (at least my red ones) are both flowering.

Phlox.

Rose Of Sharon if you want a shrub.

Hibiscus are just starting for me.

Yarrow.

Russian Sage, my Little Spires are full of happy bees right now.

Heleopsis.

Blanket flower.

Rudbeckia, like Cherry Brandy or Cherokee Sunset rather than the "black eye susans".

I don't know which fit your idea of "cottage garden" plants, but I've got them all in what I condsider my cottage style garden.

I'm also getting a few second flushes of Lavender, not sure if they will do that every year or not.