Nasturtiums, members of the genus Tropaeolum, are popular garden plants known for their vibrant, trumpet-shaped flowers and attractive, rounded foliage. They are often grown for their ornamental value, providing a cascade of color in garden beds and containers. Beyond their beauty, nasturtiums are also fully edible; both the leaves and flowers offer a distinct, peppery flavor, making them a favored garnish and addition to salads.
The Nasturtium Life Cycle and Hardiness Zones
The question of whether nasturtiums are perennials or annuals depends entirely on the climate where they are grown. Common garden varieties are classified as tender perennials, meaning they are naturally perennial but cannot survive freezing temperatures. This inherent tenderness dictates their life cycle based on the climate where they are grown.
In mild climates, specifically USDA Hardiness Zones 9 through 11, nasturtiums grow as true perennials, lasting for multiple seasons. When temperatures remain above freezing, they continue to bloom and grow. However, in regions with cold winters, freezing temperatures kill the plant, forcing gardeners to treat them as annuals that complete their life cycle in a single growing season.
Cultivating Nasturtiums for Optimal Growth
Cultivating healthy nasturtiums during the active growing season requires specific conditions. The seeds are large and are best sown directly into the garden about one to two weeks after the last expected spring frost date. Their delicate root structure makes them sensitive to transplanting. If starting indoors is necessary, using biodegradable peat pots can minimize root disturbance.
Nasturtiums thrive best when planted in full sun, receiving at least six hours of direct sunlight daily. While they can tolerate partial shade, a reduction in light typically results in fewer flowers and more foliage.
The preferred soil has excellent drainage and is relatively low in nutrients. The plants actually perform better in “poor” soil, as highly fertile soil encourages excessive leaf growth at the expense of flower production. Too much nitrogen fertilizer will specifically produce lush foliage but very few colorful blossoms.
Once established, nasturtiums are somewhat drought-tolerant. They benefit from consistent watering once a week, especially in containers, to prevent the leaves from becoming stressed and the flavor from becoming overly intense.
Overwintering Techniques for Extending the Season
Gardeners in colder zones can extend the life of their nasturtiums, forcing them to behave as perennials by providing protection from frost. The most reliable method involves preparing the plants before the first anticipated freeze. If the plant is in the ground, it should be carefully dug up and potted into a container with well-draining soil.
Trailing or bushy varieties should be pruned back lightly, reducing the stems and foliage to a manageable size of about 10 to 12 inches. Once potted, the nasturtium needs to be moved indoors to a cool location, ideally with temperatures between 55°F and 70°F, such as a bright, unheated sunroom.
The plant requires bright light, either from a sunny window or under supplemental grow lights. Watering should be reduced significantly to mimic a natural dormancy period and prevent root rot.
Alternatively, new plants can be started indoors from 4-inch stem cuttings taken before the frost. These cuttings can be rooted in moist soil or water and grown indoors over the winter, ready to move outside once the danger of frost has passed in the spring.