The Four O’Clock plant, Mirabilis jalapa, is a garden favorite known for its vibrant, late-day blooms and sweet fragrance, earning it the common name Marvel of Peru. Cultivating this plant, often grown as an annual, begins with germination from its large, black seeds. Successfully identifying the young plant in its earliest stage is a frequent challenge for new gardeners, as seedlings can often be confused with common weeds. Identification relies on recognizing the distinct characteristics of its first structures, particularly the initial seed leaves and the subsequent true leaves.
Identifying the Initial Sprout
The first structures to emerge are the cotyledons, or seed leaves, which are distinct from the plant’s later foliage. They typically unfurl within seven to fourteen days after sowing, depending on soil temperature and moisture. Four O’Clock cotyledons are irregularly round or oblong, often appearing concave or slightly flat at the ends. They are usually a bright, uniform green, reflecting their temporary role in providing initial energy for the seedling.
The stem immediately below the cotyledons, known as the hypocotyl, is stout and erect, providing a firm anchor for the emerging plant. This young stem may display a light yellow, pink, or subtle reddish hue, a common characteristic of the Mirabilis jalapa family. This coloration is often noticeable where the stem meets the soil line or on the underside of the cotyledons. The robust appearance of the young stem contrasts with the delicate stems of many weed species.
The cotyledons are thick and fleshy, reflecting the energy reserves stored within the large seed. They function briefly in photosynthesis until the first true leaves develop and take over the food-production process. Once the true leaves expand, the cotyledons begin to shrivel and eventually drop off, having fulfilled their initial purpose.
Characteristics of the First True Leaves
The first set of true leaves is the most reliable structure for positively identifying the Four O’Clock seedling and distinguishing it from other sprouts. These leaves emerge from the terminal bud located between the cotyledons and are the first structures displaying the plant’s mature leaf morphology. The true leaves grow in an opposite arrangement along the stem, with a pair emerging at the same node.
The shape of these initial true leaves is a defining characteristic, presenting as ovate or sometimes distinctly cordate. They possess smooth margins, lacking the serrations or teeth found on many common weed leaves. This smooth edge is a clear marker for the species.
The texture and color of the true leaves are specific to Mirabilis jalapa seedlings. They develop a deep, bright green coloration and often have a slightly glossy or waxy surface. The leaf tissue feels substantial and smooth to the touch, and the veins are often prominent, providing structure to the expanding leaf blade.
Early Growth Habits and Immediate Care
Once the first true leaves have fully expanded, the Mirabilis jalapa seedling enters a phase of rapid growth. The plant focuses on developing a sturdy, multi-branched structure and establishing its long, fleshy taproot. This quick development means providing the correct environmental conditions immediately is important for successful establishment.
Four O’Clock seedlings thrive when given full sun exposure, which encourages the dense, bushy growth habit of the mature plant. While they can tolerate partial shade, the most vigorous growth and abundant flowering occur when they receive at least six hours of direct sunlight daily. Proper light is necessary to prevent the young stems from becoming elongated and weak, a condition known as etiolation.
Consistent moisture is necessary for the developing seedling, but the soil must never become soggy, which can quickly lead to root rot. Gardeners should keep the soil evenly moist, watering whenever the top inch or two of the growing medium feels dry. The seedling’s preference for well-draining soil is linked to the development of its large, tuberous taproot, which stores water and nutrients.
If the seedlings were started indoors, hardening off is necessary before transplanting them to the garden. This involves gradually exposing the young plants to outdoor conditions, such as direct sun and wind, over a period of one to two weeks. Hardening off strengthens the plant’s cell walls and acclimates it to the outdoor environment, ensuring the seedling transitions successfully.