Nutritional Profile of Nasturtium; Methods of Preservation

Can you please provide me with a nutritional profile for flowering nasturtium (i.e. not watercress)? I am especially interested in the available iron content.

According to Jim Duke's Phytochemical and Ethnobotanical Databases, nasturtium (Tropaeolum majus) shoots contain 13-95 ppm (parts per million) iron. This is not particularly rich. The richest source may be dandelion leaf at up to 5000 ppm iron. Echinacea (E. spp.) root has 700-4800 ppm. Cornsalad (Valerianella locusta) whole plant has 3500-4100 ppm iron. For a complete list of the highest iron-containing plants, see:
www.ars-grin.gov/cgi-bin/duke/chemical.pl?IRON

What is the best method to preserve nasturtium leaves? I am more

concerned

about retaining nutritional value than I am about palatability.

Nasturtium leaves normally cannot be dried because of the loss of palatability. Like watercress, nasturtium leaves are eaten fresh only. But if you are not concerned with palatability then you can simply dry the leaves as you would any other herb: on screens placed in a well-ventilated, shaded location.

Can you please recommend other iron-rich herbs that preserve well?

Follow the above link for more high iron plants.