when do you stop harvesting rhubarb?

Answer 1

Stop when there is a seed stack. Generally I pick the seed stack off before it starts which allows me to harvest longer.

Answer 2

Well you aren't supposed to harvest it till the second year, then
only a little. The third year you can harvest as much as the growth
allows. You should never take all of the stalks, as it need some
to keep the roots alive.