I found this tip on figtrees.net
"The best fertilizer to use is one that is lower in nitrogen, but heavy on the calcium and phosphorous. The first feeding is done in the Spring, as soon as you move your plants from their shelter to the outdoors in a sunny location. The fertilizer consists of, 1 part superphosphate 0-20-0, 1 part 5-10-5, 1 part bone meal, and 1 part garden lime. Mix these ingredients thoroughly. Apply the fertilizer by making 4 holes at the edge of the pots, 1" in diameter and 3" deep. Fill the holes with the mixture and water thoroughly. A fig tree, three quarter inch caliber and 4' tall in a 12" pot requires 1 cup of this mixture. One month later you will begin a liquid feeding with a well balanced fertilizer, 20-20-20. Mix 1 tablespoon with 1 gallon of water, repeat this feeding every 20 days until mid-August. The last feeding will be a top-dressing done in October. Mix 1 part superphosphate, 1 part bonemeal, and 1 part garden lime. Make sure that during the summer months you water your trees frequently. Keep them moist and do not let them dry out or stressed."