Also called the Peruvian Pepper plant, this hardy annual comes in the dwarf, trailing, and climbing varieties, and exhibits pink, yellow, red, and bright orange blossoms. The stems, leaves, flowers, and pods are edible, exhibiting a sweet, pungent taste somewhat akin to yellow mustard and cress. The immature seed pods are good candidates for pickling, and end up resembling capers when the process is complete.
Nasturtiums are an excellent and attractive low-cost soil testing technique. When planted in fertile, nutrient-rich ground, they produce few flowers and many leaves. When placed in poor, lackluster dirt, they produce dozens upon dozens of flowers. Watering should be conducted once or twice a week.
All parts of the nasturtium are high in oxalic acid, meaning it has the potential to upset the stomach if eaten too much. One salad a week, or about a dozen nasturtium quesadillas are likely safe. Making wine or distilling the essence is reportedly hazardous - stomach problems associated with too much acid in the gut can happen.
Reference:
The Old Farmer’s Almanac
Various kitchen experiments with nasturtium parts.