Once again, the ƒ-stop choice is personal. Here, ƒ/5.6 softens some of the background detail. But you may also prefer the tapestry of texture afforded by ƒ/16.
Depth of field in macro shots is very much a matter of taste (Photos 2 and 3). Even the small differences between ƒ/6.3 and ƒ/8 can be seen, particularly in regard to the background. We would choose ƒ/6.3 because the white flowers have a comfortable amount of detail to still be recognizable, but beyond that, all the background clutter is taken out of play in soft focus. Generally, macro photos are most pleasing when the controlled depth of field draws attention to the primary subject while providing some sense of place, but with limited interference. Think of them like actors on a stage. You want focus on the speaking character while the supporting actors need to be engaged, but not distracting. Shoot multiple exposures with close ƒ-stop differences so you can view the subtle differences on the big screen before making your final frame choice. It's too hard to discern this degree of detail on a small LCD outdoors.
For very vertical flowers like paintbrush (Photo 6), you may not be able to carry sufficient depth of field to keep the whole flower structure sharp. Here, even ƒ/9 will only hold the top petals in focus. Look for opportunities where a pinhole light illuminates the flower like a key light in a studio. This effect works with limited depth of field rather than against it, resulting in a pleasing image.
Textures & Patterns
A 90mm macro does an excellent job with textures and patterns. These omnipresent subjects can be quite mesmerizing, and on days of poor lighting conditions for landscapes, you can almost always find interesting patterns and textures to photograph. The macro lens is well suited because it's designed to have minimal distortion and even illumination from edge to edge and corner to corner. When shooting these subjects, be cautious of careless focus.
In Photo 7, at ƒ/3.2, it's easy to be careless with depth of field because our eye tends to see the tree trunk as flat when looking through the viewfinder. Consequently, the left and lower areas of the frame aren't sharp in this simple composition that should have been easy to make perfect. Again, bracketing for depth of field is a good idea and will save you a lot of frustration when you get home.
Left: It should have been easy to make this shot perfectly sharp, but we forgot about the curvature of the trunk while looking through the viewfinder. ƒ/3.2 didn't give sufficient depth of field, and we lost sharpness at the corner.
When shooting a rather flat surface for the interest in texture (Photo 8), it's not necessary to go overboard with a small ƒ-stop beyond ƒ/16. An increase in depth of field can be mitigated by unacceptable amounts of diffraction. Do some tests with your own macro to get a sense of the trade-off between depth of field at smaller apertures and diffraction.