An in-camera montage (two image overlay). One image is daffodil as seen here; the 2nd is the same daffodil shot with the macro lens wide open and the flower completely out of focus (just a large yellow blur). Overlaying the large blur with the normal shot provides this hazy glow. The amount that the 2nd image is out of focus is a variable that you can play with for different effects - however, it must be put out of focus by getting *LARGER* and not smaller. Try it, you'll like it.
This is known as the Orton Technique (named for a Canadian photographer who introduced it using film slides by sandwiching two slides together in a mount). It has since been popularized by folks like Andre Gallant (another Canadian) who calls them Dreamscapes and Tony Sweet among others.
A miniature daffodil shot in the sun room this morning. Good thing it's indoors as there's a ton of snow coming later today.