I had nasturtium (I can't be spelling that right) in a 5 gal pot with a fig last summer. Both seemed right as rain, in fact I knew the fig needed water when its companion looked like it needed water. It served as a living mulch and made nice salad additions

~Chills

I put onion and schalotts in the fig's 5gal pots in the green house last fall, and cut the green shoots off all winter to ad to dishes. Now the figs are 2 years old, I put them out in the ground and left the onions, and will harvest them later. Kind of intence gardening, using all the space you can.

I planted dwarf marigold in some of my fig pots. They both seemed happy and they looked nice.

I have horehound growing in with my big fig tree. I thought it was a good thing, now I know it is. Thanks to this thread I went looking for some info online.....

HOREHOUND: (Marrubium Vulgare) like many varieties in the mint family, the many tiny flowers attract Braconid and Icheumonid wasps, and Tachnid and Syrid flies. The larval forms of these insects parasitize or otherwise consume many other insects pests. It grows where many others fail to thrive and can survive harsh winters. Blooms over a long season, attracting beneficial insects almost as long as you are likely to need them. For best results use horehound directly as a companion plant. Stimulates and aids fruiting in tomatoes and peppers.

Wow, I learned something new!!
Peace,
Little John

Would planting clover in the pot with a fig help with the fig's nitrogen needs? I've heard that clover can collect nitrogen from the air.