I have a dogwood...supposed to be Cherokee Chief I believe, that's been in the ground for nearly 15 years and has only flowered one year, and with only a few blooms (and they were white no less). It does seem to form the flower bracts but they are green like the regular leaves (see photos). I have two other dogwoods that bloom beautifully but this one just puts out these non-descript leaf-flowers. Any suggestions as to why or how I can stimulate it to produce?