Nasturtiums are known for their vibrant, edible flowers and ease of cultivation. Gardeners often wonder if they will return next year; the direct answer is that they readily reseed themselves. This ability to self-sow allows them to become a persistent annual presence, though success relies heavily on local conditions.
The Process of Natural Seed Dispersal
Nasturtium plants produce large seeds following the bloom cycle. After the flower fades, the plant forms a three-segmented fruit capsule that houses the seeds. It takes approximately 40 to 50 days from pollination for these seeds to reach full maturity. Once mature, the seed pods dry out and detach from the parent plant. Since they lack a specialized dispersal mechanism, they typically drop straight down onto the soil surface beneath the vine. This creates a high density of seeds ready for the next season. The seeds have a hard outer coat, which protects the embryo and regulates germination timing.
Environmental Factors Influencing Germination Success
While seeds are successfully dispersed, their ability to sprout the following spring is determined by external environmental factors. Nasturtiums are tender annuals, meaning the parent plants cannot survive deep winter cold. Self-seeding is most reliable in mild climates where the soil does not freeze solid for extended periods. Successful germination requires the soil to warm to a consistent temperature range, optimally between 55°F and 65°F. This warmth signals the end of the cool season and encourages the seed to break dormancy. The hard seed coat must first soften through exposure to consistent moisture. The integrity of the soil surface also plays a role. Since the seeds are heavy, they germinate best when lightly covered, typically about one-half to one inch deep. Excessive soil disturbance, such as vigorous tilling, can bury the seeds too deeply or expose them to too much light, which is unfavorable for germination.
Practical Management of Volunteer Nasturtiums
Gardeners can influence self-seeding by adjusting end-of-season practices. To actively encourage a new crop of volunteer nasturtiums, the most effective method is leaving the spent plants intact. Allowing the flowers to fully mature and the seeds to dry and drop naturally maximizes the number of seeds available for spring growth. If the goal is to prevent self-seeding and maintain control, the most direct action is to deadhead spent flowers before they form seed pods. This cuts off the reproductive cycle. For seeds that have already dropped, a heavy layer of mulch applied in the fall can be effective, as it smothers the seeds. Should a large number of volunteer seedlings appear in the spring, they are easily managed through thinning. These young plants are simple to pull up or transplant to a more desirable location, provided care is taken with their roots. Early removal is the simplest way to control the spread without resorting to chemical measures.