How can I remove the legend title in ggplot2?

Question

I have a question concerning the legend in ggplot2.

Say I have a hypothetical dataset about mean carrot length for two different colours at two farms:

Answer 1

I found that the best option is to use + theme(legend.title = element_blank()) as user "gkcn" noted.

For me (on 03/26/15) using the previously suggested labs(fill="") and scale_fill_discrete("") remove one title, only to add in another legend, which is not useful.