A white Echinacea? Or Hibiscus. Otherwise, a white Japanese Anemone, but they're a little later.

What about a white-flowered Sedum, such as 'Iceberg'?

Miss Lingard phlox is a treasure. Also white malvas would be nice--long bloom.

It's highly unlikely you'll get anything matching that description to flower the entire summer.

I haven't grown "Miss Lingard" - but phlox "David" has a long flowering period, up to one and a half months here. White cleome (an annual) would probably flower much of the summer if kept deadheaded.

Phlox and anemones are good suggestions. The latter bloom in the fall. Malva would also be good choice for your zone and also white hibiscuses and white platycodon, which have long seasons, though they start in summer, not spring.

I would nominate Kalimeris pinnatifida as among the longest blooming, if it were hardy for you. It is listed in the link below as zone 6, but other sources say zone 5 or even 4. It starts in July and goes on through the fall.

The best advice is to look in other gardens in your area and see what you like that does well for other people. If it grows well for them, you can probably grow it, too.

Here is a link that might be useful: Kalimeris pinnatifida

an asiatic white lily?

Here is a link that might be useful: white lily

Thank you for the suggestions! I really like the look of phlox---have always been wary to try it because of the mildew issues, but I might give it a try next year and see how it goes. Thanks again for all of your input!

Phlox "David" is touted as being mildew-resistant, which in my experience it most definitely is. Doesn't bloom until mid-summer, though. For earlier flowers how about one of my favorites, the very hardy and reliable campanula persicifolia which comes in a beautiful pure white (alba) and blooms for quite a long time. Gary

If you are worried about mildew, stick with David. I'm not sure I've ever seen mildew on it, under all sorts of conditions.

My Galtonia sometimes called "Summer Hyacinth" is in bloom right now. White bloom on tall stems. An easy to grow bulb that multiplies. Al

Gaura Whirling Butterflies flowers all summer long.

Miss Lingard phlox is a different phlox species/hybrid from the other phlox mentioned. It blooms a little earlier than the usual summer phlox and does not get mildew for most people.

It used to be a standard in every perennial garden and is also often called wedding phlox because it was used in wedding bouquets picked from the garden.

But it is still widely available--see Google and Google images. It isshowy, with large blossoms, and fragrant too--a real winner. Make sure you are getting the true Miss Lingard.

I'd like to see a picture of your front porch garden with the Obedient plant. I enjoyed your pictures earlier when the allium were blooming.

What we are growing as 'Miss Lingard' mildews horribly. I don't remember where it came from, since it arrived maybe 15 years ago. Any suggestions as to where to get the real one?

Digitalis 'Camelot white), oriental poppies, Dierama (there are white cultivars) leucanthemum, or the smaller 'snow thimbles), Gypsophila paniculata, Scabious ochraleuca, nicotiana sylvestris (short-lived perennial sometimes), Galtonia candicans, cimicifuga, Campanula (various) Penstemon white bedder, snowstorm,artemisia, aster diviricata iris, agapanthus (hardiest are Headbourne Hybrids)Achillea ptarmica 'The Pearl', thalictrum delavayii album, Oenothera pallida

Mad_gallica, it may be that some nurseries just put the label Miss Lingard on any white phlox. There are several sources on Google but I can't vouch for them re this plant. The true Miss Lingard has narrower, thicker leaves than summer phlox.

Sorry to say that all I can suggest is a local or online nursery you really trust.

Wow, I've been busy googling---who knew there were so many to choose from! You all gave me so many more choices than I found on my own when I did searches for "tall white perennials" :)

Campanula, I love the foxglove idea.... When does it bloom and for how long? Also, the Penstemon is very pretty---I have never seen it before! I definitely need something bold there--- So far I think phlox, digitalis, and penstemon are my best bets. Even the obedient plant wasn't showy enough to be seen from the street---I need a big 'ol white flower. The lilies would work too... but I'm not a huge fan. As far as a picture, I never took one when the obedient plant was blooming! It was pretty, but didn't quite give the 'pop' that the allium did.... which is what prompted a new search :) Thanks so much for all of your help---lots to think about

Mad Gallica, Bluestone Perennials carries Miss Lingard and I would trust them. Plus good prices and very healthy plants.

Thanks A2zmom, I might add it into to my next order. However, if the current ones came from where I think they did, it is a reputable place.

BTW, I have some David seedlings that seem to be as disease resistant as their parent.

If you want something REALLY tall, try some white flowering hollyhocks (surprised no one mentioned this). The time of year that it blooms really depends on when you start them from seed.

I would recommend David if your site gets plenty of sun. I have on in a mostly sunny location, it started bloominbg in Mid June (Zone 5a, IL) and still goes strong now at end of July. But I have two more in a morning shade and afternoon sun location, one developed serious mildew last year and 2nd one started mildew this year. It still flowers, but leaves are very bad so I pulled them out.

Another reliable and long blooming option is Shasta daisies. I have the Alaska (up to 2-3 tall) and Snow Lady (~ 12-18 in), both of them bloom from Mid June to early August.

Phlox David has proved to be a very aggressive plant with me, devouring everything in its path. And it does get mildew. I would suggest Veronicastrum virginicum album, which is a polite plant(not the whole summer though). Also Thalictrum polygamum(creamish white)