I now understand why the residents of coastal North Carolina warned me that despite torrential rains at some times, lack of rain was often an issue and with the sandy soil that promptly drains, plants dry out here very fast despite high humidity.
Our late, great, self-reliance guru JRandomFreeper had similar soil. He was able to improve it by adding biochar, which he made by soaking homemade charcoal in a bucket with rabbit poop and an aerator.
Some experimenters on Permies.com have reported similar results with biochar. It can absorb its own volume in water, but doesn’t release that water easily. One person even tried burning soaked char in a fire, and it took hours for it to dry enough to burn, and burn slowly at that. But, plants are able to tap into that water easily through mycorrhizae (beneficial fungi that are symbiotic with plants).
There is even one person on Permies who is experimenting to see if biochar can retain water well enough to combat desertification.
As I recall, when dealing with soil that drains too well, large chunks of biochar, roughly the size of a thumbnail, worked better than finely-ground or powdered. Too small and the char gets drained away with the water. Too large and the pieces cause the same problem as rocks of that size.
I hope that helps!