I used to put in polemonium caeruleum (the blue, because it also comes in white) and two other white plants that bloomed at the same time - salvia cocinea snow (which also comes in coral), double feverfew and blue borage (which also comes in white) and nicotiana alata.
But that was because I was doing white on white or white and blue, which may be a bit drab for you.
And of course any of the salvia farinaceas would be lovely. Here is white, blue and the blue and white strata.
Oh no, not too drab! I love white on white. That's what I want. I didn't think Polemonium would work because it needed more shade than the Lilies. I was thinking Nicotania or Salvia but I wasn't sure Salvia would be blooming when the O.L. 'Casa Blanca' was blooming.
Thanks so much for responding and giving your suggestions. I think we're in the same camp when it comes to plant choices and combinations.
I should have provided a pic. None of them are great but nicotiana alata and salvia cocinea Snow Nymph do bloom at the same time. I stand corrected on polemonium because unless you deadhead it you won't get it to rebloom in time. You can see that it's showing seedheads.My polemonium was in sun - it did better then than now, in shade.
In terms of timing, the spent lilies to the right are regale.
By the way, this was a very neglected part of my yard!
I have never grown Polemonium--I like it. In fact, it is quite pretty. The little bit of blue peaking up is so sweet. D G says it sh. grow in shade, but other sites have said sun. Just goes to show, you have to do research. Your pictures are just the look I am after.
What about Nepeta fassenii 'Snowflake"? Does it bloom after the O. Lilies?
The salvias you mentioned would work but they are annuals. I eventually want this to be mostly perennials.
Would Salvia or Nepeta bloom while the O. L. are in bloom?
These are really interesting questions. I have pictures of nepeta snowflake (do note, this is historical, and my bloom is later than yours) in bloom in April and in bloom in September and early October. I have a picture of snowflake in bloom while Silk Road nearby is in heavy bud - it's on May 27. It's a really bad picture, but you can see the two clumps of Snowflake, one in the foreground, one in the rear. Horribly neglected, which is why there is some grass there. (pic 1.)
In the same neglected spot, here it is in mid-June reseeding (the white borage is self-sown, another really rocking plant, by the way). See the wonderful little clumps? You can just pick them up and move them whereever you like.
I have polemonium caeruleum in both sun and shade and it blooms in both and in my opinion it blooms better in more sun. I had mine on the northwest side of my property, where it got blazing afternoon sun, and it was stunning. I took some clumps to my new house and it is shyer to bloom in shade.
Pic three shows the site with afternoon hot sun. If you have the kind of plants that can take sun with moiture, like the epimedium, thalictrum and lady fern in this picture, you have a good spot. My epimedium thrived in sun, and it's thriving now in shade. I think that polemonium will bloom repeatedly if you deadhead it. And I love the fern effect. And I wanted it to seed and give me new plants - and by the way, it does that readily, and you can just pick them up and move them.
Pic four shows the morning sun. I positioned the ferns all the way against the building to keep them from getting too much of it.
Pic 5. But the polies got full sun because they were nmore forward. And this is 10:00 in the morning.
Pic 5 is a part of my garden that could get 90 degree heat. This is in June of last year. The polemonium is in very full bloom.
There are several perennial salvias that would also work. I love nemerosa Rose Queen. You have to deadhead it, but it is terrific. And if you deadhead it, it keeps blooming. This plant is at least severn years old.pic 1
One of my absolute favorites is salvia tesquicola. I grow it with peonies, roses and lilies. It blooms for months if you deadhead it. pic 2.
It's a tidy plant (early season) pic 3. At home is was in bloom with regale.
Here are two at my new house last April. pic 4.
And then, in May, with peony Lois. It bloomed into November, and you do need to tear out some of the excess - but what a plant! pic.5
Like nepeta snowflake, it's beautiful, bulletproof, will not push out other plants' root systems (which nicotian alata tends to do), long blooming and drought tolerant.
Did I answer your questions? If not, please ask again. It took me ten plus years to figure out some of these things, with a few of the usual failed experiments, and I am really happy to share my experiences.