Pick nasturtium seeds from nasturtium plants while they're still green and tender. As the growing season progresses, they will turn tan and become hard. At that point, they're past their prime.
Place harvested nasturtium seeds in a bowl of cold water and swirl them around to remove dirt and debris. The dried stems and flowers will float to the surface.
Add clean nasturtium seeds to an 8-ounce mason jar. Fill a small saucepan with water, vinegar, salt, and sugar, and bring to a boil. Add a few sprigs of fresh dill to the jar, then pour the pickling solution over the pods.
Seal the jar, then place it in a dark, cool spot. Allow to pickle for at least one to two weeks. Store in the refrigerator after that.
Notes
If you think you might find the flavor too strong, brine the seeds in a mixture of two cups of water and ¼ cup salt for 3 to 5 days. Rinse the seeds and continue with the recipe steps.
The extra brining time mellows out the flavor, but I personally prefer the strong flavor.
Pickle the nasturtium seeds for at least 2 weeks; longer would be even better.
Store pickled nasturtium seeds in the refrigerator for up to 6 months.
If pressure canning, pickled nasturtium seeds can be stored in a cool, dark location for up to a year.