Nasturtiums (\(Tropaeolum majus\)) are valued for their easy growth, vibrant flowers, and edible, peppery leaves. Identifying seedlings early is simple because their initial growth stages present two distinct leaf forms before the familiar, mature foliage develops. Knowing these visual cues allows gardeners to distinguish the young plant from surrounding weeds and ensure a healthy start for the edible annual.
The Initial Sprout: Cotyledons
The first leaves to emerge from the soil are the cotyledons, which are temporary embryonic leaves contained within the seed. Their primary function is to provide initial nourishment for the seedling to establish roots and begin photosynthesis. These initial sprouts are typically pale green or light yellow-green due to stored energy and lack of full photosynthetic development.
Nasturtium cotyledons generally display a rounded or slightly elongated kidney-bean shape, differing from the plant’s mature appearance. They often appear thick or fleshy, serving as the plant’s first energy source. These structures are not part of the mature plant’s permanent foliage and will eventually yellow and shrivel once their function is complete.
Distinctive True Leaves
The primary identifier for a nasturtium seedling is the emergence of the true leaves, which grow from the shoot apex above the cotyledons. These leaves are miniature versions of the mature foliage and look strikingly different from the first pair of leaves. The true leaves have a unique, nearly circular or shield-like form.
This shape is technically described as “peltate,” meaning the leaf stalk, or petiole, attaches at the center of the leaf blade rather than at the edge, resembling a miniature umbrella or a water lily pad. Prominent, light-colored veins radiate outward from this central attachment point, creating a distinctive pattern across the deep green surface.
Emergence Timeline and Seedling Care
Nasturtium seedlings typically emerge from the soil between seven and fourteen days after planting. This timeline is influenced by soil temperature, which should be consistently warm for quick sprouting. Once the seedlings have emerged and developed their first set of true leaves, they may require attention to spacing.
If multiple seedlings are growing close together, it is important to thin them out to allow the strongest plants room to develop. Seedlings should be provided with ample light, such as a sunny windowsill or supplemental grow lights, to prevent them from becoming long and weak. Keep the soil consistently moist but never waterlogged, as overwatering can quickly lead to damping-off disease.