Call conditional statement object into ifelse

First, I want to create and object containing my conditional statement. Then, I want to call this statement into ifelse. Thanks in advance for your help!

Example:

library(dplyr)

dd <- iris

# This code does the job but it gets messy when I have many statements
dd <- dd %>%
  mutate(Box = 
           ifelse(Sepal.Length > 5 & Species == "setosa", "Box_1", NA))


# This code doesn't work but it's what I'd aim
st <- Sepal.Length > 5 & Species == "setosa"

dd <- dd %>%
  mutate(Box = 
           ifelse(st, "Box_1", NA))