Cilantro (Coriandrum sativum) is a popular annual herb that adds a distinctive flavor to many global cuisines. While simple to grow from seed, successful cultivation depends almost entirely on precise timing. This herb is highly sensitive to heat and will quickly end its leafy growth phase if conditions are not optimal. Understanding the right planting windows is the path to an abundant harvest.
Optimal Seasonal Timing for Cilantro
Cilantro is a cool-season crop, thriving when air temperatures are consistently below 70°F. The ideal time to sow seeds occurs during two main windows: early spring and late summer. In spring, planting should begin as soon as the soil is workable, typically two to four weeks before the last expected frost date. Direct sowing outdoors is recommended because cilantro develops a delicate taproot that dislikes transplanting disturbance.
Successful germination happens when the soil temperature is consistently between 55°F and 68°F. Sowing in this cooler period allows the plant to produce foliage before the onset of summer heat. The second opportunity for harvest is in late summer or early fall, approximately six to eight weeks before the first expected frost. This timing allows plants to establish themselves as temperatures drop, offering a longer, productive growing period.
Preventing Premature Bolting
The primary challenge in growing cilantro is preventing premature bolting—the rapid switch from leafy growth to sending up a flower stalk to set seed. This process is triggered by two main environmental factors: rising air temperatures and increasing daylight hours. When the air temperature consistently rises above 75°F, the plant shifts its energy to reproductive growth.
Bolting is signaled by a change in leaf shape, where the broad, flat foliage is replaced by narrow, feathery leaves that have a diminished and often bitter flavor. To delay this natural transition, consistent cultural practices must be maintained. Providing partial afternoon shade for spring plantings helps mitigate the heat stress that causes bolting. Applying organic mulch, such as straw, is also helpful for keeping the soil temperature below 75°F.
Consistent and adequate moisture is equally important, as water stress can also trigger flowering. Plants kept evenly watered and protected from the harshest afternoon sun will remain in their leaf-producing phase for a longer duration. Choosing slow-bolting varieties, such as ‘Calypso’ or ‘Santo,’ provides a genetic advantage against flowering quickly in warming conditions.
Strategy for a Continuous Supply
To ensure a steady supply of fresh leaves beyond a single harvest, gardeners must employ succession planting. This strategy involves staggering the planting of small batches of seeds rather than sowing the entire crop at once. Sowing a new row of seeds every two to three weeks creates a rolling harvest that replaces plants as they reach the end of their productive phase.
This method is most effective during the cool spring and fall windows. For spring planting, start the first batch as soon as the soil is ready, and continue sowings until daily high temperatures begin to climb past 70°F. The fall-planted cilantro often provides the longest and most abundant yield because the plants are established as temperatures decline.
Starting the fall succession in late summer, about eight weeks before the first frost, allows the plants to grow into the cooling weather. In regions with mild winters, planting can continue into late fall and early winter, sometimes requiring the protection of a cold frame or simple row cover to extend the harvest.