Don't forget that you'll get more DOF by backing off a bit (increasing the distance between the camera sensor and the focus point). By filling the frame and then some, you're creating the situation where DOF will be tight even at high f-stops. It's your choice, and if you want the blossom filling the frame you're in the process of finding out what the extra challenges are. It's also your choice whether to tolerate OOF petals or whether you want the whole blossom to be sharp (or acceptably so). There are merits to both possibilities.

A third choice is whether you want the OOF petals just at the back of the blossom or at the back and the front. Personally I find OOF foreground objects a bit offputting when they're prominent or eye-catching, and I usually think that it looks like a mistake. But there's no shortage of people who find it completely acceptable or see it as a way to focus attention on the centre of the blossom. Just be aware when you're given advice that the adviser may have a personal bias behind what he/she is saying.

If you're zooming in close because you want a highly focused view of the blossom, and perhaps want most of the viewer's attention on the heart of the blossom, another possibility is to shoot the blossom wide enough to give some free space round it (or most of it) then add a fairly heavy vignette in PP. When done properly a vignette can be a very effective way to focus attention and it can look quite dramatic. And as a bonus, the whole blossom is there for the viewer's enjoyment.

Agreed. Shoot hundreds, some the same and some with the slightest change. For so close to the subject with this pixel resolution, where you focus can be the difference. For the center disk, if described as a clock, it would seem the florets at the edge about 7-oclock should be sharpest. Test various focus points from the outer edge with slight changes to the 3rd row in, comparing each image at f/11 and every 1/3-stop through f/20.

Bela1950, look too at your focus method. Are you using the camera's LiveView and the 10x zoom and manual focus? All ideas to test on a static subject with a digital camera.