Nasturtiums (Tropaeolum majus) are vibrant, easy-to-grow annuals prized for their shield-shaped leaves and edible, peppery flowers. They are a popular choice for home gardens, providing continuous color and a unique culinary ingredient. Propagation is accomplished through two primary methods: starting from seeds or using vegetative cuttings.
Starting Nasturtiums from Seed
Sowing seeds directly into the garden is the most common method for propagation. Nasturtium seeds possess a hard outer coat, which can slow water absorption and delay germination. To accelerate this process, gardeners can perform scarification by gently nicking the seed coat or soaking the seeds in warm water overnight before planting.
Nasturtiums are highly sensitive to frost, so direct sowing should only occur after the last expected frost date, when the soil temperature has warmed to a consistent 55°F to 65°F. For an earlier bloom, seeds can be started indoors in biodegradable pots about two to four weeks before the final frost, minimizing root disturbance later. Plant the prepared seeds approximately one-half to one inch deep in a light, well-draining seed-starting mix.
Maintain consistent moisture in the planting medium, but avoid saturation, as overly wet conditions can cause the seeds to rot. Under ideal conditions, germination typically occurs within seven to fourteen days. Once seedlings emerge, place them under bright light or in a sunny window to prevent them from becoming leggy.
Propagating Nasturtiums from Cuttings
Cuttings are useful for cloning the parent plant, preserving specific traits like variegated foliage or rare double-flowered varieties. Begin by selecting a healthy, non-flowering stem tip, ideally four to six inches long. Make a clean cut just below a leaf node, as this area naturally contains the highest concentration of root-producing hormones.
Remove all lower leaves from the cutting, leaving only the top two or three leaves to minimize moisture loss through transpiration. While nasturtiums can root without assistance, dipping the cut end into a rooting hormone powder can increase the speed and reliability of new root development. The cutting can be placed into a small pot filled with a moist, sterile potting mix or a mixture of perlite and peat.
An alternative method involves submerging the cut end in water, which allows for visual monitoring of root formation. Place the cutting in a location that receives bright, indirect light and maintain high humidity around the foliage. Roots should begin to emerge within a few weeks, signaling readiness for the next stage of growth.
Transitioning Young Plants
Once seedlings have developed their second set of true leaves, or rooted cuttings show substantial growth, they are ready for the final outdoor environment. If starting plants indoors, pot them up into individual four-inch containers to give the delicate roots space to expand. Nasturtium roots are fragile, requiring care during this initial transplanting.
Before permanently moving the young plants into the garden, they require a process called hardening off, which acclimates them to outdoor stressors like sun, wind, and temperature fluctuations. Over a period of seven to ten days, gradually expose the plants to outdoor conditions, starting with just one or two hours in a sheltered, shaded location. Increase the daily exposure time and sunlight intensity incrementally.
This gradual adaptation toughens the plant’s cell structure and reduces the risk of transplant shock. Wait until all danger of frost has passed and night temperatures are consistently mild before transplanting the hardened-off plants.
Ongoing Maintenance and Site Requirements
Nasturtiums thrive in conditions often considered poor for other flowering annuals. The ideal site features full sun, providing at least six hours of direct light daily, though they can tolerate partial afternoon shade. They prefer poor to average, well-draining soil that is not overly rich in nutrients.
Excessive soil fertility, particularly high nitrogen levels, directs the plant’s energy toward producing lush foliage at the expense of developing numerous flowers. While young plants require consistent moisture to establish their root systems, mature nasturtiums are somewhat drought-tolerant. Regular watering during dry spells will encourage continued blooming throughout the season.
To promote a bushier habit and extend the flowering period, deadhead the spent flowers regularly, preventing the plant from diverting energy into seed production. Nasturtiums are occasionally used as a trap crop because aphids are particularly drawn to their foliage. A simple, forceful jet of water from a hose can dislodge and control small infestations of these common garden pests.