They retain the vibrant red color indefinitely when harvested from April to June or October to January when they are without their summer foliage. This is when we harvest and dry our dogwood branches for the best color.  This is also a great time to catch them at the peak time to preserve the dogwood branches so they will last and look brilliant for a long time in your arrangements.
Dogwood stems aren't very brittle and can also be soaked like cane and woven into wreathes or baskets. The longer dogwood branches usually have little 6 inch or so stems off of them so they do look nice it a very tall arrangements.

Dogwood branch short stem length: 12-28 inches
Dogwood branch long stem length: 48-60 inches (sold out)
Dogwood branch color: red
Branches per bunch: 10
Bunches per case: 12