Nasturtium (Tropaeolum majus) is a widely cultivated annual prized for its vibrant colors and edible qualities. The leaves and blossoms have a distinct peppery flavor, making them popular in culinary use as a garnish and salad ingredient. Gardeners often start these plants in pots indoors to gain an early advantage or to nurture specific varieties before the last frost. Understanding the correct seeding technique in containers ensures the plant’s successful transition outdoors.
Selecting the Proper Pot Size
Nasturtiums have a root system sensitive to disturbance, making the choice of container important. For starting seeds indoors, select a small pot to minimize the need for intermediate transplanting. A diameter of 2.75 to 3 inches is generally suitable for initial growth, or standard cell trays can be used.
These dimensions allow the seedling to establish itself before moving to its permanent location. Using biodegradable pots (such as peat or coir) eliminates the risk of transplant shock, as the entire pot can be planted directly into the ground. If growing the plant to maturity in a container, the final pot should be at least 8 to 12 inches deep and wide to accommodate the mature root ball of a single plant.
Optimal Seeding Density and Depth
For small starting pots or cells, sow one to two seeds per container. Planting two seeds is often recommended as insurance against a low germination rate, which is common due to the hard coating on nasturtium seeds. If seed viability is high or if using a smaller cell tray, a single seed per container is sufficient.
To prepare the seeds, pre-soak them in warm water for 4 to 24 hours just before sowing. This softens the thick seed coat, promoting quicker water absorption and improving germination speed and percentage. Once prepared, plant the large seeds at a depth of 1/2 to 1 inch below the soil surface. Adequate depth is important, as darkness is required for effective germination.
Managing Seedlings After Germination
Once seeds germinate (typically within 7 to 14 days), focus on ensuring the strongest plant thrives. If two seeds sprouted, perform “thinning” to prevent resource competition. Thinning should occur once the seedlings develop a few sets of true leaves (the leaves appearing after the initial cotyledons).
To thin, select the weaker or smaller seedling and use small scissors or shears to snip it off cleanly at the soil line. Cut the stem rather than pulling the seedling out, as pulling can disrupt and damage the delicate roots of the remaining plant. Seedlings must remain protected until all danger of frost has passed.
About 7 to 10 days before moving them outdoors, gradually introduce the seedlings to outside conditions through “hardening off.” When transplanting the hardened-off seedlings to their final location, minimize root disturbance. Planting the root ball at the same depth it was growing previously helps prevent stem rot and ensures a smooth transition to vigorous growth.