All of my in ground figs are in coastal NC, very sandy soil that is also infested with root knot nematode (RKN).
I dig a large hole at least 3x what I need, mix in organic potting mix, compost, or manure - usually about 2 cubic feet. The tree STAYS in, or is planted first in a 5 gallon bucket. Bottom of bucket is removed, and the tree, with the bucket, is planted leaving about 2 inches of the bucket above the soil line. Then I top with plenty of bark mulch.
RKN only live in the top foot or so of the soil (they need light), and are repelled by organic containing soils (though the reason for this is unknown), so the combination of planting the bucket and amending with organic material should keep the RKN at bay. Mulching should provide a continuous protective "shield" of organic matter to keep them away.
This is my first year with in ground figs, all of them grew very well.