Plants just wilting and dying.

[Cyclone]

I have only ever really had problems when planting into the Earth.

 

Maybe try and reduce your variables next time by putting them in pots

with your own little concoction of soil mix. Maybe wash then

sterilise your ground sand with oxyplus (H2O2) to kill anything

that may be residing in their.

 

I like the sea salts theory

 

Could just be blatant salt spray build up on the leaves and they are

getting roasted in the sun?

 

Cyclone -

[Psychonaut]

You say the root ball was pathetic, have they struggled from the start?

 

I am just thinking your saying its an old beach/sand dune but sounds a bit more than just sandy soil? You might need to remove a heap of the old ground and bring in some dirt then compost maybe.

 

Of course could be what other have suggested too

 

Cheers mate.