Tropaeolum majus, commonly known as Nasturtium, is a vibrant and versatile plant cherished by gardeners for its striking, colorful blooms and distinctive foliage. Native to the Andes Mountains, this easy-to-grow annual or short-lived perennial is widely cultivated. All above-ground parts, including the leaves, flowers, and unripe seed pods, are edible, offering a peppery flavor that enhances salads and other dishes. Its attractive appearance and versatility make propagation a rewarding endeavor.
Propagating Nasturtiums from Seed
Propagating nasturtiums from seed is the most common and straightforward method due to their large seed size and relatively quick germination. To prepare seeds, soak them in lukewarm water for 4 to 24 hours before planting; this softens the hard seed coat and speeds up germination. Alternatively, gently nick the seed coat (scarification) to aid water absorption and germination. After preparation, plant the seeds immediately.
Nasturtiums can be sown directly outdoors after the last frost has passed, or started indoors 2 to 6 weeks before the last frost date for an earlier bloom. For direct sowing, plant seeds approximately 1/2 to 1 inch deep and about 10 to 12 inches apart in well-drained soil. When starting indoors, use biodegradable pots like peat or coir to minimize root disturbance, as nasturtiums are sensitive to it. Place one or two seeds about 1/2 inch deep in each pot.
Nasturtium seeds germinate best in soil temperatures between 55°F and 75°F (12°C and 24°C). They require darkness for germination, so ensure seeds are adequately covered with soil. Keep the soil consistently moist but not waterlogged throughout the germination period. Sprouts typically emerge within 7 to 14 days.
Propagating Nasturtiums from Cuttings
Nasturtiums can also be propagated from stem cuttings, particularly during warmer growing seasons. This method preserves specific plant characteristics or creates more plants from existing ones. To take a cutting, select a healthy stem approximately 4 to 5 inches long, making the cut just below a leaf node.
Remove any lower leaves from the cutting, ensuring at least two sets of leaf nodes remain, and pinch off any flower buds. This helps the plant focus energy on root development rather than foliage or bloom production. Rooting hormone is optional, as nasturtiums root easily without it.
Cuttings can be rooted in either water or a well-draining potting medium. For water rooting, place the cutting in water, ensuring no leaves are submerged, and change the water regularly to prevent decay. For soil rooting, fill a small pot with sterile, lightly dampened seed-starting mix or potting soil. Insert one-third to one-half of the cutting’s length into the medium, gently firming the soil around the stem. Place the pot in bright, indirect light, and roots should form within a week or two.
Caring for Newly Propagated Nasturtiums
Once seedlings have developed true leaves, or cuttings have established roots, they are ready for care. If multiple seedlings emerged in one pot, thin them to the strongest plant to ensure adequate space and resources. When transplanting, handle them gently as nasturtium roots are sensitive to disturbance. For seedlings started in biodegradable pots, plant the entire pot directly into the garden or larger container to minimize shock.
Young nasturtiums thrive in full sun, requiring at least six hours of direct sunlight daily, though they tolerate partial shade in hotter climates. Ensure the soil remains consistently moist, especially for newly transplanted plants, to help them establish and reduce transplant shock. However, avoid overwatering, which can lead to issues like powdery mildew.
Before moving indoor-started seedlings outdoors, gradually acclimatize them through “hardening off.” This involves exposing them to outdoor conditions for increasing periods over a week or two, protecting them from harsh wind or intense sun initially. Nasturtiums perform well in average to poor, well-drained soil and do not require heavy fertilization; excessive nitrogen promotes leafy growth at the expense of flowers.
Troubleshooting and Common Questions
Legginess, where stems become long and spindly, is a common issue with nasturtium seedlings, particularly those started indoors. This often results from insufficient light, as seedlings stretch to reach a light source. To prevent this, ensure seedlings receive ample bright light. Excessive heat can also contribute to leggy growth.
If seeds fail to germinate, several factors could be at play. Inadequate moisture, incorrect soil temperature, or a very hard seed coat can prevent sprouting. Ensuring proper pre-soaking or scarification, consistent soil moisture, and optimal temperature can improve germination rates. While nasturtiums are easy to grow, young plants can occasionally face challenges.
Pests like aphids, mealybugs, and whiteflies can affect young nasturtium plants. Nasturtiums are sometimes used as a trap crop, attracting pests away from other garden plants. For minor infestations, a strong jet of water can dislodge aphids, or larger pests can be removed by hand. Overly rich soil can also lead to more foliage and fewer flowers; avoid excessive fertilization for optimal blooming.