I don't have figs that large yet, but I do something similar with my mature blueberries that are in large pots. They are half sunk in the soil, and mounded around them (similar to your straw) is free, ground city mulch. It's more brown in color, is easy to spread, and over time decomposes well. It makes the plants look as if they are planted directly in the ground, keeps the pots cooler and the weeds from growing.