I'm looking at fold changes relative to a negative control. I'm not interested in displaying genes with a negative FC, is there a way to just display the positive/right side of the volcano plot? I've tried setting the xlim to start at zero, but this doesn't work.

Indeed, one just needs to pre-filter the input results table / data-frame for those genes with positive fold-changes.

For example:

subset(res, log2fc > 0)

Kind regards,

Kevin