Combine dried hibiscus blooms and 2 cups water in a medium saucepan. Bring to a boil over medium heat. After 5 minutes, remove from heat. Strain.

Add guavas and hibiscus concentrate to a blender. Blend until smooth. Add sugar and blend on low speed to mix well. Strain again.

Add 3 cups ice to blender. Add lime juice, strained hibiscus/guava mixture, tequila, triple sec and blend until smooth.

Run a lime around rim of margarita glasses. Rim with salt. Pour blended mixture into glasses. Garnish with a guava slice and a dried hibiscus bloom. Serve.