Samut Sakhon is a leading province for sea salt farming in Thailand (1). The picturesque salt farms with white fields sprawling across the border with Samut Songkhram have provided a back drop for many holiday snapshots.
Salt farming is seasonal. The best chance to catch the view is during the dry season between February and May. Sea water is first pumped into the fields. Once the water has evaporated, layers of salt remain to be collected by the farmers.
It is best to combine this with a visit to the railway market and floating markets which are nearby.