There are two kinds of Nasturtiums. Climbing Nasturtium (Tropaeolum majus) and Dwarf Nasturtium (Tropaeolum minus). Both are vining plants. Climbing Nasturtium grow up to 6′ in length and are good for climbing up trellises, fences or poles. Dwarf Nasturtium grow up to 12″ in length and are good for borders, windowboxes and hanging baskets.
Although you only see red flowers in this picture, Nasturtiums grow a mixture of yellow, orange and red coloured flowers on the same plant.
Amy mentioned eating the flowers, which can be done, but typically the leaves are eaten. Young leaves are used as a pepper substitute in pepper-restricted diets and have an unusually high vitamin C content. It is the immature green seeds that can substitute for capers. If you are germinating these indoors, you should grow them in peat pots, as they do not like to have their roots disturbed.
Nasturtiums are used a lot in companion planting, as they attract aphids from other plants. They also repel carrot rust flies and beetles. They are a good companion plant for melons and most vegetables, including tomatoes.
If you have pet rabbits, as I do, Nasturtium is also one of the herbs you can grow for them as forage.
— Courtesy of Suzy