Cilantro, the popular leafy herb, is botanically the same plant as coriander, which is the spice derived from its seeds. Unlike many garden herbs that tolerate summer heat, successful cilantro growth for leaf harvest relies entirely on planting during precise cool-weather windows. The timing of planting dictates whether a gardener enjoys a plentiful harvest of aromatic leaves or a quick transition to seed production.
Identifying the Ideal Planting Window
Cilantro thrives within a relatively narrow temperature band, making timing the single most defining factor for leaf production. The plant grows most vigorously when temperatures are consistently between 60 and 70 degrees Fahrenheit, though it can tolerate the range of 50 to 85 degrees Fahrenheit. Planting should occur in early spring, as soon as the soil is workable and the last significant frost danger has passed.
The second optimal planting time is in late summer or early fall, when the intense heat of the season begins to break. This fall window often provides the longest possible harvest period because the shortening days and cooling temperatures naturally prolong the plant’s leafy, vegetative stage. Planting in the fall allows the cilantro to grow rapidly through the mild autumn, often providing a harvest well into the following spring.
The primary challenge in growing cilantro is “bolting,” the plant’s reproductive response to high heat and long daylight hours. Once the average temperature consistently rises above 75 degrees Fahrenheit, the plant rapidly shifts its energy from producing leaves to forming a tall central stalk, flowers, and seeds. This transition renders the leaves unusable for culinary purposes, as they become diminished in flavor and acquire a bitter taste. Therefore, the goal is to plant early enough in the spring or late enough in the fall to complete the leaf-growing cycle before heat stress triggers premature flowering.
Succession Planting for Continuous Harvest
Given the plant’s short lifespan before bolting, a single planting yields fresh leaves for a limited duration. To ensure a steady supply throughout the cool season, gardeners must employ succession planting. This involves sowing a small batch of seeds every two to four weeks, rather than planting the entire supply at once. This staggered schedule ensures that as one batch begins to mature and bolt, a younger batch is simultaneously coming into full production.
Succession planting is most effective during the spring and fall growing windows. As temperatures rise in late spring, gardeners can attempt to delay bolting by planting seeds in a location that receives partial shade, particularly during the afternoon heat. Consistent soil moisture also helps keep the roots cool, mitigating the heat stress that causes the plant to bolt. Harvesting the outer leaves frequently helps prolong the vegetative phase by preventing the plant from focusing its energy on reproductive growth.
Planting Specifically for Coriander Seeds
If the primary goal is to harvest coriander, the plant’s dried seeds, the planting strategy must be counter-intuitive to leaf production. The objective shifts from delaying bolting to actively encouraging it, since flowering is necessary to produce the seeds. Planting cilantro later in the spring, allowing it to mature right as the summer heat and long days arrive, will accelerate its life cycle. This timing encourages the plant to quickly send up a flower stalk and set seeds.
For seed production, the plants should be spaced farther apart, typically eight to ten inches, to allow each plant ample room to grow large and support its seed-laden stalks. The foliage will naturally become sparse and bitter once the plant bolts, but the flowers will attract beneficial insects before developing into seeds.
Harvesting Coriander Seeds
The seeds should be left on the plant to fully mature until they transition from a bright green color to a tan or light brown hue. Once the seed heads are dry, the stems are cut and hung upside down in a cool, dry area, allowing the mature coriander seeds to easily drop into a collection container.