According to the Royal Horticultural Society of England,
"To encourage figs to bear crops it’s a good idea to restrict their root growth; by restricting the plant’s leafy growth, the plant will produce more fruit. You can do this by creating a planting pit; growing the plant in a container; and plunging a container into the ground.
To prepare a planting pit, dig a hole 60x60x60cm (2x2x2ft). Line the sides of the holes with patio slabs, setting them 2.5cm (1in) proud of the ground to prevent the roots from spreading over the top of the soil. Leave the bottom unlined, but add a layer of rubble or broken bricks and crocks to 10–15cm (4–6in) deep, to prevent roots penetrating the soil underneath.
Dig around the outside of a planting pit every couple of years with a sharp spade to ensure that no roots have escaped."
Do you think it really works? Less roots=more fruit?