How to increase space between facet_wrap labels and panels in R ggplot2?

Question

I want to increase the vertical space between the labels (setoda, versicolor and virginica) and their respective panels. How can I do this? The regular options like panelspacing and margins don't seem to have an effect.

library(ggplot2)
library(grid)


ggplot(data = iris, aes(x = Sepal.Length, y = Sepal.Width, color = Species)) +
             geom_point()  +
facet_wrap( ~ Species) + 
theme(strip.text.x = element_text(face = "italic")) + 
theme(strip.background = element_blank())

Answer 1

One option would be to increase the margin around the strip.text:

library(ggplot2)

p <- ggplot(data = iris, aes(x = Sepal.Length, y = Sepal.Width, color = Species)) +
  geom_point() +
  facet_wrap(~Species) +
  theme(strip.background = element_blank())

p +
  theme(strip.text.x = element_text(
    face = "italic",
    margin = unit(rep(50, 4), "pt")
  ))

Or using margin() and increasing only the bottom margin:

p +
  theme(strip.text.x = element_text(
    face = "italic",
    margin = margin(4.4, 4.4, 50, 4.4, "pt")
  ))