How narrow could the passages (approx. 1 m in length) for the GARDENA Robotic Lawnmower in my garden be?
That depends on the Robotic Lawnmower.
R38Li, R40Li, R45Li and R50Li: The minimum width is 90 cm between the boundary wires.
R70Li, (smart) SILENO / SILENO+: The minimum width is 60 cm between the boundary wires.