My belief is that your trees will benefit from being heavily mulched, partly from added nutrients but mostly from moisture retention and the tendancy of mulch to keep the root zone cooler when summer temps start heating things up.

Once established, fig trees seem to do well even in poor sandy soils.

Here in the deep sands of NW Florida amending the soil with pine bark or compost and composted cowmanure,mushroom compost,(limestone if needed), Heavy mulch is recomended. Anything to help hold moisture and cool the soil and I understand the mulch and organics are good for earthworms and bad for nematodes.
I have an LSU Purple I need to plant. I want to try grafting some weak growers onto LSU Purp root stock and see it helps.
I believe their claim that it is Nematode 'Resistant' and every little bit of advantage helps.
I'm losing a lot less trees now that I am basicly treating their planting hole allmost like I would a large pot. Our sand has nothing for the tree except drainage. Any moisture retention or food for the plant has to be provided by you.
Good Luck
R

Thanks both.

"Our sand has nothing for the tree except drainage."
Same here. And as they used to say for citrus on the central Florida ridge, "just holds the tree up."

I'll try the big hole and amended backfill approach. I have access to composted elephant and giraffe manure. We'll see if that helps! Plus some limestone. A big state office building near here dumps its grass clippings in an available pile so I hopefully have an endless supply of high-N mulch for the hauling.

Good Luck Gonebananas.
Just wanted to add, that when I plant a large tree in the new loose,organic medium I usually drive a piece of rerod or bamboo down to hold the tree till it can take hold.