You'd need to supplement the soil with iodine, although maybe plants would respond well to some kind of water made with kelp. That might be a sustainable option for someone who lives by the beach and has access to ample amounts of seaweed/kelp (that has been rinsed in freshwater or rainwater) to use in their compost or as mulch, or they could soak rinsed kelp in fresh water and give that water to the plants. Shale could potentially be another soil addition.
You'd need to supplement the soil with iodine, although maybe plants would respond well to some kind of water made with kelp. That might be a sustainable option for someone who lives by the beach and has access to ample amounts of seaweed/kelp (that has been rinsed in freshwater or rainwater) to use in their compost or as mulch, or they could soak rinsed kelp in fresh water and give that water to the plants. Shale could potentially be another soil addition.