When a cilantro plant begins to grow wispy, feathery leaves that look remarkably like dill, it is a common moment of confusion for many gardeners. The plant, Coriandrum sativum, is unique because its identity changes depending on its maturity. The fresh, broad, flat leaves are called cilantro, while the plant’s dried seeds are known as coriander. This dramatic change in foliage signals a normal but often misunderstood stage in the plant’s life cycle.
The Reason for the Transformation: Bolting
The shift from broad, lobed leaves to delicate, dill-like foliage is the physical manifestation of a process called bolting. Bolting is the plant’s biological mechanism for transitioning from vegetative growth, which produces the leaves we harvest, to reproductive growth. This change is driven by the plant’s internal clock and is its signal to flower and produce seeds before its life cycle ends.
Once the plant begins to bolt, it sends up a thick, central stalk that elongates rapidly. The feathery leaves, known as the mature foliage, develop along this flowering stalk. They are morphologically distinct from the juvenile leaves and are designed to support the stem and the eventual flower heads, called umbels. This rapid vertical growth is a direct result of the plant allocating its energy away from leaf production to ensure the next generation of seeds.
Factors That Trigger Early Bolting
Cilantro is a cool-season annual, meaning it thrives in mild weather and possesses a natural tendency to bolt when conditions become less favorable. The primary external trigger that accelerates bolting is high temperature. When temperatures consistently rise above 70°F to 75°F (about 21°C to 24°C), the plant perceives a threat to its survival and rushes to produce seeds.
The number of daylight hours, or the photoperiod, is another major factor, as cilantro is a long-day plant. As the days lengthen, the increased exposure to light signals to the plant that the ideal growing window is closing. These extended daylight hours act in conjunction with rising heat to trigger the hormonal shift that initiates the bolting process.
Environmental Stressors
Environmental stressors can also prematurely force the plant to bolt, even if the temperature or light conditions are not extreme. Irregular watering or allowing the soil to dry out causes moisture stress, which the plant interprets as a survival risk. Similarly, root binding in a container or insufficient nutrients can prompt the cilantro to prematurely switch to reproduction as a defense mechanism.
Managing Bolted Cilantro and Extending the Harvest
While bolting is inevitable for Coriandrum sativum, gardeners can employ several techniques to delay the process and extend the harvest of the preferred foliage.
Delaying Bolting
Techniques to delay bolting include:
- Planting seeds in a location that receives afternoon shade. This helps moderate the soil and air temperature during the warmer parts of the day.
- Maintaining consistent moisture is important, as keeping the soil evenly moist prevents the stress that triggers early bolting.
- Choosing slow-bolt varieties, such as ‘Santo’ or ‘Calypso’, which offer a longer window for leaf production compared to traditional types.
- Using succession planting, which involves sowing a small batch of new seeds every two to three weeks. This ensures a continual supply of young, non-bolted plants.
Once the plant has bolted and the feathery leaves have appeared, the flavor of the foliage changes, often becoming milder or more bitter. However, the entire plant remains usable, offering a secondary harvest in the form of the spice coriander. Allowing the plant to flower and produce green, berry-like seeds will yield fresh coriander. If left to dry and turn brown on the plant, these seeds can be collected, dried, and used as the familiar culinary spice.