I have a question regarding calculating a standard deviation.

I have been taking plant measurements of a series of weeds. I had 4 plots in total, with 10 plants in the first plot, 3 in the second, 9 in the third and 13 in the fourth. Unfortunately I didn't take the plant biomass of each, rather, I took a total weight of each of the plants. As such, I have a total mass of 149.57 grams in the first plot, 12.91 grams in the second plot, 54.69 grams in the third plot and 23.47 grams in the third plot.

So when I calculate my standard deviation is my 'n' value 4, or is my 'n' value 35? I am wondering if I have limited my degrees of freedom by lumping the total biomass of all the pants in the plots.

Regards to all who respond to this! I appreciate it.