Fixing label clipping in subplot

Hi. I have constructed a subplot made up of a phylogeny and a heatmap. I am wondering if any of you might know how I could extend the bounds of the canvas as to avoid clipping the axis labels?

Thank you!

This is what the heatmap looks like before subplot:

This is the code I used to make the subplot:
subplot(p, p2, nrows = 1, margin = 0.0, shareX= TRUE, shareY = T)

where p is the heatmap and p2 is the dendogram.