Petunias are prized annuals, known for their abundant, trumpet-shaped flowers and long blooming season, making them a popular choice for containers and garden beds. Since commercial petunia seeds are extremely small, often appearing as fine dust, starting them indoors requires a keen eye. Successfully growing these flowers from seed hinges on accurate identification during the earliest stages, especially when tiny petunia seedlings emerge alongside other garden sprouts. Knowing the precise visual markers of the plant ensures the desired flowers are nurtured.
The First Leaves: Cotyledon Stage
The first structures to emerge from the seed coat are not true leaves but temporary leaves called cotyledons. Petunia seeds typically germinate and produce these initial leaves within seven to fourteen days after sowing, provided they have adequate warmth and light. These initial leaves are primarily responsible for supplying the young sprout with stored food until the plant can begin full photosynthesis.
Petunia cotyledons are characteristically small, often appearing no larger than a pinhead, and are generally oval or slightly elongated in shape with smooth edges. Unlike the adult foliage, the surface of the cotyledons is smooth and lacks the distinct texture of the mature plant. This uniformity makes identification challenging, as the cotyledons of many different plant species look quite similar.
Identifying Features of True Petunia Leaves
The definitive characteristics of the petunia seedling appear with the development of the true leaves, which emerge directly above the cotyledons. These true leaves are miniature versions of the mature plant’s foliage, providing the first reliable identifier for the species. The shape of these leaves is ovate to slightly spatulate, meaning they are somewhat spoon-shaped with a rounded tip.
A distinctive feature of petunia true leaves is their texture, which is hairy and somewhat sticky due to a dense covering of fine, glandular hairs called trichomes. These trichomes are noticeable even on small seedlings and are a strong visual confirmation that the sprout is a petunia. The leaves initially grow in an opposite arrangement on the stem, before transitioning to an alternate pattern as the stem elongates. The foliage presents a mid-to-dark green color, and some varieties may exhibit a slight purple or reddish pigment on the stem near the soil line.
Differentiating Petunia Seedlings from Weeds
The appearance of the true leaves is the moment a gardener can confidently distinguish a petunia seedling from common garden weeds. Many weeds that germinate at the same time often have smooth, glossy leaves, which creates a sharp contrast to the petunia’s unique fuzzy and slightly sticky surface.
The velvety or hairy feel of the petunia leaf is a dependable physical trait that many common weeds lack. Another distinguishing factor is the initial growth habit of the petunia seedling, which tends to stay low to the ground and develop a rosette of leaves before forming an upright stalk. This contrasts with many weeds that shoot quickly upward on a slender stem to compete for light.
Some petunia varieties possess a faint, slightly musky fragrance when the leaves are gently rubbed, which is a rare characteristic among opportunistic weed seedlings. It is advisable to wait until a seedling has at least two sets of true leaves before thinning the crowded sprouts, ensuring that only the desired petunias are kept.