Cilantro is a popular, yet sometimes frustrating, cool-season herb known for its quick transition from a leafy plant to a flowering stalk. This change is called “bolting,” and it represents the plant shifting its focus from vegetative growth (producing leaves) to reproductive growth (making flowers and seeds). Bolting is the plant’s natural imperative to ensure its survival by producing the next generation of seeds, known as coriander, before its growing season ends.
Environmental Factors That Cause Bolting
The primary trigger for cilantro to bolt is temperature stress, as it thrives in cooler weather. When temperatures consistently rise above 75°F (24°C), the plant perceives these conditions as unfavorable for long-term growth. It rapidly initiates flowering as a survival mechanism, accelerating its life cycle to produce seeds before it dies.
Another significant factor is photoperiod, or the length of daylight hours, because cilantro is a long-day plant. As the days lengthen in late spring and early summer, typically exceeding 12 hours of light, this signals a change in season that prompts the plant to enter its reproductive phase. Stressors like inconsistent watering or becoming rootbound in a container also contribute to early bolting. When the plant senses poor or limited resources, it rushes to flower and set seed to complete its life cycle.
Changes in Flavor and Plant Structure
Once cilantro begins bolting, observable changes occur in its physical structure and flavor profile. The plant’s central stem elongates rapidly (stem extension), raising the flowers up for better pollination. The leaves also undergo a distinct change, transitioning from the broad, flat cilantro leaf shape to a more feathery, wispy, and deeply lobed appearance on the flowering stalk.
The flavor of the leaves shifts, often becoming bitter, sharp, or less potent. This change is linked to an alteration in the production of essential oils responsible for the herb’s characteristic taste. While the leaves remain safe to consume, their quality for culinary use significantly diminishes once the plant commits energy to seed production.
Strategies for Delaying Flower Production
Since bolting cannot be entirely stopped, the focus is on practical strategies to prolong the leaf-harvesting period. Succession planting is the most effective technique, involving sowing small batches of seeds every two to four weeks. This ensures a continuous supply of young, non-bolting plants as older ones begin to flower.
Providing afternoon shade mitigates the primary cause of bolting: heat stress. Position the plant where it receives protection from the intense mid-day sun, or use a light shade cloth, to keep the plant and its root zone cooler.
Consistent and deep watering is necessary to prevent the drought stress that triggers early flowering. Maintaining evenly moist soil helps keep the roots cool and signals stable conditions for continued leaf growth.
Regular harvesting, especially using the “cut and come again” method by trimming the outer leaves, encourages the plant to produce more foliage from the center. Promptly snipping off any developing flower stalks can also momentarily delay the plant’s commitment to seed production.
Harvesting Coriander Seeds
When cilantro bolts, it offers a secondary harvest: coriander, the spice derived from the seeds. The delicate white or pink flowers eventually turn into small, round seed heads. To harvest coriander, allow these seed heads to mature and dry completely on the plant.
The seeds are ready for collection when they transition from green to light brown or tan and the stems feel brittle. Once ready, cut the stems with the seed heads attached and hang them upside down in a cool, dry, and well-ventilated area for about two weeks to finish curing. The dried seeds can then be gently rubbed off the stems and stored in an airtight container.