The sweet pea (Lathyrus odoratus) is a popular ornamental annual prized for its fragrance and colorful flowers. Successfully growing this vining plant begins with identifying its seedlings immediately after they emerge. Knowing the visual characteristics of a healthy young sweet pea helps confirm germination and differentiate the plant from common weeds. This guide details the appearance of a healthy sweet pea seedling, from initial emergence to the development of its climbing structures.
First Emergence: Cotyledons and Hypocotyl
The first signs of growth typically appear within five to ten days of sowing, involving the emergence of the stem and seed leaves. The initial stem, known as the hypocotyl, pushes the seed out of the soil. It is pale green or white, appearing sturdy and straight. This structure stretches to seek light, making a well-lit environment crucial immediately after emergence.
The first leaves are the cotyledons, or seed leaves, which are distinct from the plant’s mature foliage. Sweet pea cotyledons are typically thick, fleshy, and rounded or oval in shape, displaying a pale green color. These temporary leaves act as an energy source before true photosynthesis begins. They do not resemble the mature, compound leaves and will eventually shrivel and drop off.
Identifying Features of True Sweet Pea Leaves
Confirmation of a true sweet pea seedling comes with the development of the true leaves, which appear above the cotyledons. The true leaves are compound, meaning they are divided into smaller subunits called leaflets. These leaflets are elongated or ovate, often displaying a bluish-green or grayish-green hue.
The most distinctive identifying feature is the specialized structure that develops at the tip of the leaf stem: the tendril. The tendril is a thin, wiry modification of the terminal leaflet that is sensitive to touch. It begins to appear once the seedling has two to three sets of true leaves. The tendril functions to wrap around nearby supports, allowing the plant to climb. The stem itself is slender and slightly grooved, sometimes described as “winged.”
Common Seedling Appearance Problems
Visual characteristics can signal distress or poor growing conditions. Legginess, or etiolation, is a common problem characterized by a pale, stretched, and thin stem. This weak appearance results from the seedling growing upward to find adequate light, often caused by insufficient light exposure or excessive heat.
Discoloration is another indicator of stress. Yellowing of the cotyledons or true leaves (chlorosis) often points to a nitrogen deficiency or overwatering. Overwatering leads to waterlogged soil, which suffocates the roots and inhibits nutrient uptake, resulting in the yellow appearance. A sudden collapse of the stem at the soil line, where the tissue appears pinched and dark, signals damping off, a fungal disease that rapidly kills young seedlings.