(Editor's Note: This article was originally published on December 16, 2010. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
I love nasturtiums, Tropaeolum majus, also known as Indian cress, and initially only used them in my garden as companion plants for my vegetables since they deterred a long list of garden pests and I liked their beautiful deep brilliant colors too. Then I discovered the nasturtium was classified as an herb because the entire above-ground plant was edible with a peppery flavor like much of the cress family. It is antimicrobial, antibacterial, and possibly anti-fungal too. The plants have medicinal properties, and are high in vitamin A, Bs (1, 2, & 3), C, with phytonutrients, calcium, iron, phosphorus, manganese, carotenoids, flavonoids, and protein. They also contain mustard oil which creates the pungent and peppery taste.  What a fantastic multi purpose plant!
A few years ago, I came across an old-time recipe for pickling the nasturtium seedpods (see Nasturtium-Seed "Capers" recipe below) to create frugal mock, or poor man's, capers. I have also seen them referrred to as capuchin capers. I wondered, "what is a caper?" The caper is used as a condiment, and is actually a pickled flower bud from a caper bush, Capparis spinosa, found growing primary in the Mediterranean region of the world.
It was time to harvest the nasturtium seedpods once the cool fall weather finally came around. I plucked the hard, unripe, light-green brain-looking globs (pods) off the flower vines. What seemed like a lot of pods, barely filled a tiny two-ounce jar!
I used the recipe I had found to make the mock capers with vinegar and dill, then set the little jar in the fridge (beside the jar of real capers) and waited anxiously for the day I could use them. After a couple of weeks, I opened the jar of homemade capers, had a taste, and was not at all impressed! They tasted nothing like the tangy-salty flavor of the real capers. Plus, the capers were soft and squishy and the nasturtium seedpods were hard and crunchy. More experimenting was needed, and I would try other recipes.
The pickled pods were not bad tasting, just not what I had expected, not caper-like. They had a pleasant enough flavor and could be used in salads, soups, and stews where a peppery-mustardy flavor would be appreciated. I learned that nasturtium seedpods could be pickled like cucumbers and other vegetables, salt-brined, and/or mixed with herbs and spices to produce a myriad of flavors. The pickled pods can be used much the same as a caper, but again, with a different taste.
I think one of the salt-brining recipes would yield better results, and if the pods were cooked (to soften them) with some minced garlic, and a milder vinegar, the taste and texture would be an acceptable substitution for capers, but they would definitely have a peppery undertone. According to "The Old Foodie" (a popular historical foods blog), throughout history other plant parts were pickled to be used as a substitute for capers, like cucumbers chopped in small pieces, marsh marigold buds, green peas, and berries from the pepperidge tree. 
RecipesHere are a few frugal caper recipes using nasturtium seedpods that you might like to try and decide for yourself about the flavor, texture, and use.
From the vinegar tincture method suggested to extract the herbal properties of the plant, I believe there may be some potential medicinal benefits in using other parts of the plant along with the little pods. I imagine one of the brightly colored flowers and a whole leaf creatively placed in a tiny jar with the seedpods, pickling vinegar, and spices, would make a beautifully presented garden-crafted gift that is as nutritious as it is practical!
There is a common practice of drying the nasturtium seedpods and loading them in a pepper mill to use as a substitute for black peppercorns, which makes more sense than capers to me, so that will be this year's experiment with my little pods!
The information in this article is provided for general information purposes only and does not constitute medical advice.
Special thanks to my dear friend Pam (DG's pdhickey) for her beautiful nasturtium photos! The caper comparison photo belongs to me.
 Herb of the Month. June/July 2006 Nasturtium Tropaeolum majus. International College of Herbal Medicine.
 Janet Clarkson. Capers, Real and Not. The Old Foodie. Nov 18 2010.