Try different varieties. Plenty of them bloom here, this past summer they did not even wait until September. You can see multiple kinds plants around the northeast parking area at the Center for Urban Horticulture, in Seattle. Locations for some of the now rather frequent street tree plantings in Seattle can be found in Trees of Seattle - Second Edition (2006, Arthur Lee Jacobson).

I already have THREE different varieties, want to concentrate on trying to get them to bloom -- any suggestions re: compost? fertilization?

There is never a guarantee of crape myrtles blooming in our climate :-) Typically, it doesn't get hot enough for a long enough period of time to encourage reliable blooming on most. The ones in the CUH parking lot, which is pretty much an ideal location for crapes (full sun, reflected heat = a 'hot' spot), are even sporadic in their performance. I'd also assume that establishment and maturity of the plant will have something to contribute to the frequency of blooms as well.

Paul Bonine of Xera Plants (an Oregon wholesale grower) has done a lot of trialing of these for our climate and he suggests focusing on earlier flowering varieties. This is his list of recommended cultivars:

'Pink Velour' - early bloomer
'Acoma'
'Arapaho'
'Biloxi'
'Hopi'- early bloomer
'Natchez'
'Tuscarora'
'Zuni'

It's the climate, not the compost. You have to pick the right ones, same as with orchard apples and hybrid roses there are many different kinds - probably not that hard to end up with three that are not the best for this area.

I can speak from experience with Lagerstroemia 'Tuscarora' here in cool summer Berkeley, Calif, that this is not a good choice for guaranteed bloom. Four summers out of five I only get flower buds that may just barely bloom by late October, and the fall rains and onset of cooler temperatures stop them in their tracks. Just a few miles inland or further south where the summer temps may be 10F warmer each day, they bloom just fine. In those rare summers that we get some sustained warmth starting in late spring into early summer, it is another story.

Bottom line, they may just need more heat than you can give them. Enjoy them for the bark and fall color, but expecting great blooming may be beyond your control...

I have a 'Zuni' that is more than ten years old, probably closer to fifteen and it has bloomed every single year.

I know Portland is warmer than Seattle but just thought I'd throw in my experience anyway.

I don't fertilize it other than a topdressing of compost.

Two more to add to the list of early bloomers: 'PDXtra Early Red' (a Xera Plants exclusive) and L. chekiangensis.

I planted two one gallon 'Petite' I can't remember the rest of their names and they died the first winter. Paid a pretty penny for them at the Hardy Plant Society sale a couple years ago.

Seattle is considered very marginal for CMs to bloom. I guess if you have them next to a hot parking lot it's the best bet. I am gambling on a whole slew of CMs in my yard in Vancouver WA and I am quite encouraged by the results so far. The purple magic dwarf ones blooming great. Nice bloom on one Tuscarora. Some small flowers on a couple of Midnight Magics, even though they are very young plants. Catawbas didn't bloom, but I will give them another year or two. My Natchez didn't bloom, but they are known as easy bloomers and there are ones in town that bloomed great, so I am confident these will do well, given time. The only one I am very doubtful will bloom here is my Cherry Dazzle. As to dying in winter: yes, small branches can freeze to death in winter. If a plant is too small, the whole thing might die in winter. I have a bunch of small ones in pots I will pu in the garage from nov to February for one or two winters, and then plant outside. As long as they are big enough they should grow like crazy even if the little branch tips die in winter. I had some small ones I planted last fall and they died to the ground in winter, but lo and behold they grew back from the roots this summer and one even flowered.

Some pruned to a single trunk and a good 20 feet tall were very showy this summer in SE Portland.

Larry did you drive by my house ;) 'Zuni' was gorgeous. I meant to take a picture but forgot.

I have 3 Tuscaroras in my yard that I planted this year in March or so. They all bloomed in August. I live in Clark County, WA.

I got three tiny trees of "white dogwood" and "Laegerstromia" from the Arbor Society--does anyone know which cultivars they are known to use?