A typical potato cell requires you to use energy to make some copper and some zinc. The metals store this energy and, if put in the right medium will give up the energy as electricity. Potato is a possible medium. So you then insert these metals into some potato.
The potato could be in the ground, but there is no benefit to the potato being there. The potato isn't providing any energy or electricity, that comes from the zinc and copper.
A typical potato cell has an emf of about 0.8 volts, and an internal resistance of several thousand ohms (lets say $2000\Omega$. If you want more power you can make a battery of lots of potatoes.
If you have 300 potatoes you could have a voltage of 240 volts. That is mains voltage in the UK. Nice! What happens if I want to run my laptop off of this.
Well my laptop apparently will draw up to 0.4 Amps of mains power at 240volts, so it has an effective resistance of $V/I=240/0.4 = 600\Omega$. But the potato battery has an internal resistance of $600000\Omega$. The voltage will be divided over my laptop and the internal resistance in the ratio 600:600000 = 1:1000, so of the 240Volts, my laptop only gets 0.24V,
and a current of about 0.0004 A.
I can't power my laptop like that.
With sufficient potato cells wired in both series and in parallel it would be possible to get some useful power from them. But you will run out of copper and zinc pretty quickly, because most of the energy generated is used to overcome their internal resistance. The energy is used to gently warm the potatoes.