Never pool together then weigh. Always weigh individually then pool. This is because you will need a measure of variability in your results such as standard deviation or standard error for statistical comparison. It's good to have records of variance even if you never use it! :-)

I think measuring individually and then pooling (means) is better. This will help you compute the confidence interval for the pooled weight. You can see variability in the data.

Dear Anitha Mani

If you are taking 10 seedlings from each replicate, then you can weigh them together and calculate seedling biomass per unit area (in field experiment) or mean seedling weight ( in laboratory or pot experiment) for each replicate and analyze the data on the basis of experimental design. Otherwise, it is better to weigh the seedlings individually and calculate standard error or standard deviation.

Best wishes

Kazem Ghassemi-Golezani

Thank you Andrew Paul McKenzie Pegman, Tadesse Fikre Teferra and Kazem Ghassemi-Golezani for clarifying my doubt.