Hi everybody. Just chiming in... I'm moving back to the area after living in Tennessee for 30 years We are on the process of transitioning our small farm and nursery operation to Blaine Washington (zone 6B to zone 8A) so I feel set this is a topic I can help with.
The key to crepe myrtles IS heat as far as blooming and growth. I have several specimens I'm bringing with me and I'm going to try the old trick of planting them against a south-facing heat collecting wall. I'm pretty confident that will work. I'm not too worried about the winter part of it because we have much colder Winters in the mountains of Tennessee where I'm from ... And the crepe myrtles are from 😅
And honestly even if they never Bloom for you, the bark on these things is gorgeous. Many cultivars have bark that is striped and peels like a eucalyptus tree. So they are always
beautiful and an interesting Garden addition even in the winter. They can grow immensely tall in the south. I once purchased a specimen that was already 40 ft tall when I bought it at a nursery outside Memphis Tennessee that specializes in crepes. Of course I'm not expecting that kind of growth here LOL.
Since I'm back in the Pacific Northwest after 40 years away, I'm hoping a lot of you on this forum can help me readjust my gardening skills for my new environment LOL