Please keep in mind these two things: (1) Most of the sakura fragrance and flavor is in the leaves, so use the leaves for cooking, and the blossoms mainly for decoration or to add very slight fragrance to green tea. (2) Try to use the deep pink blossoms of the Yae-zakura tree. These tend to bloom later than other varieties of sakura, and have large, multi-layered petals. Choose a tree that is far from the exhaust fumes of motorized traffic.
yae-zakura blossoms..........200 grams
salt (first stage)..........50 grams
ume-zu (plum vinegar, either white or pink will do)..........4 Tablespoons
salt (second stage)..........50 grams
1. Remove the blossoms from the branch at the point they are connected to it, stem and all. Rinse them gently, but thoroughly, in cold water. Drain the water, and pat the flowers dry using paper towels.
2. Toss the first 50 grams of salt with the blossoms and place the salted flowers in a small bowl. Place a weight (400 grams) over the flowers, cover all with plastic wrap, and set aside overnight. This will draw out the excess water from the flowers.
3. Next day, gently squeeze out the water from the flowers, then sprinkle them with the plum vinegar. Place a weight (this time only 100 grams) over the flowers, cover all with plastic wrap, and let sit for three days.
4. Spread the flowers (still with their stems) over a paper towel-lined, woven bamboo tray so that no flower overlaps with another. Place the tray in a dry, shady place for three days.
5. Toss the dried flowers with the second 50 grams of salt, and store them in a small, clean, screw top jar to keep at room temperature for future use. Or you can keep the plum vinegar-steeped flowers from step #3 in the refrigerator and eat them like pickles.
More detail and photographs of the procedure can be found at this Japanese site.