Parsley (Petroselinum crispum) is often confusing for gardeners because it is treated as both an annual and a perennial. The herb is naturally a biennial plant, meaning its full life cycle spans two distinct growing seasons. Because its leaves are the desirable part for culinary use, and their quality changes drastically in the second year, most home gardeners cultivate parsley as an annual. Understanding the differences between these classifications is necessary to manage parsley for a successful harvest.
Defining Annual, Biennial, and Perennial Plants
Plant life cycles are categorized by the time it takes for a species to germinate, grow, flower, produce seed, and die. Annual plants complete this entire cycle within a single growing season. They sprout in the spring, reach maturity, set seed, and perish, typically with the first hard frost. Common examples include tomatoes, corn, and many bedding flowers.
Perennial plants live for more than two years, returning season after season from the same root system. These plants may die back in winter, but their root crowns survive the cold and regenerate new growth in the spring. Shrubs, trees, and herbs like chives and mint fall into this long-lived category.
Biennial plants require two full growing seasons to complete their life cycle. They focus exclusively on vegetative growth, developing roots, stems, and leaves during the first year. After surviving cold dormancy, they flower, produce seeds, and die in the second year.
The Biennial Nature of Parsley
Parsley’s two-year life cycle is dictated by vernalization, a period of cold exposure necessary to induce flowering. During the first year, the plant establishes a deep taproot and a rosette of lush, flavorful leaves. This vigorous leaf production is the plant’s primary focus, storing energy in its root to survive the winter.
If the plant survives the winter, the cold temperatures trigger a hormonal shift. In the second year, the plant rapidly shifts energy from leaf production to reproduction. It sends up a tall, rigid flower stalk, a process known as bolting, which can reach up to 30 inches in height.
Once the plant bolts, the remaining leaves become sparser, tougher, and develop a noticeably bitter flavor due to concentrated essential oils. The plant produces flat-topped clusters of small yellow-green flowers, which are attractive to beneficial insects. After the seeds mature, the entire plant dies, completing its two-year cycle.
Managing Parsley for Continuous Harvest
Gardeners manage parsley to maximize its first-year vegetative stage, as the goal is to harvest fresh, mild-flavored leaves. The best strategy for a continuous supply is succession planting, which involves sowing small batches of seed every few weeks throughout the growing season. This ensures that new, first-year plants are always maturing as older plants begin to fade.
Treating parsley as an annual means removing the plant before or after its first winter, or allowing it to die back in climates with harsh freezes. In mild climates, the plant may occasionally survive longer or be slow to bolt. However, the quality of the second-year foliage is usually diminished, making replanting the better choice for flavor.
If a second-year plant is allowed to grow, bolting can sometimes be delayed by consistently snipping off emerging flower stalks. Harvesting leaves from the outer stems of the rosette encourages the plant to produce more foliage and maintains vigor. Once a plant has fully bolted and the leaves have turned bitter, it is best to remove and replace it with a new plant to restart the cycle.