Q: I have four crape myrtle tree/bushes at the edge of my patio. They have all grown fairly large and appear to be thriving. However, the one tree (a 'Sioux') did not produce any flowers this year, and last year it only had two or three on it. Prior to that it was filled with beautiful dark pink flowers. It looks healthy and continues to put out new growth but no buds or flowers have appeared. Do you have any idea as to what the problem might be?
A: It could be a lot of things, but a few I'd check out first would be:
1.) What kind of sun are you getting? Full sun all day is best. If nearby trees have grown to start shading that particular crape myrtle, that'd be a strong possibility.
2.) Weather. Lots of cloudy, rainy weather isn't good for crape myrtle bloom. Some varieties are more sensitive to that and to weather in general, i.e. some types form buds earlier and may get wiped out by a late frost while a later-budding type will be OK. Hotter, drier weather next year could put your 'Sioux' back into a good bloom without doing anything.
3.) Excess nitrogen. If you're fertilizing the lawn around the crape myrtles with a high-nitrogen lawn nitrogen four times a year, that could be throwing your crape myrtle nutrition out of whack. High nitrogen would be good for leaf and woody growth but can reduce flowering. The fix for that is to cut back on fertilizer or to get a soil test and see if your phosphorus and potassium is in good supply and balance.
4.) Japanese beetles. This bug likes crape myrtles. It's possible beetles ate your 'Sioux' flower buds before you ever noticed them. But once the beetles are gone by August, you should've started seeing new buds and then flowers. I've seen beetles pick out specific varieties of the same species but let others alone.