Cilantro can be a wonderful addition to any herb garden, but cilantro seeds can be tricky to grow. Cilantro seeds, otherwise known as coriander, have hulls that should be softened before planting. The seeds germinate fairly quickly, and the cilantro plants mature quickly, so to have a continuous harvest of cilantro, it is necessary to plant the seeds often throughout the growing season. The seeds prefer rich, loose soil and should be planted at a shallow depth. The climate greatly affects cilantro seeds, and both soil and air temperature should be on the cool side for successful growth.
Seeds that are harvested directly from cilantro plants have protective hulls. The hull should be softened and preferably removed prior to planting. To soften the hulls, the seeds should be soaked in a shallow dish of cool water. The outer hull can easily be rubbed off by rubbing two seeds against each other. The seeds should be allowed to dry thoroughly before planting.
When planting cilantro seeds, it is best to use a loose, rich, fast-draining soil with a pH range between 6.5 and 7.5. The seeds do well when sown thickly in large containers and thinned out later when the plants are approximately 4 inches (about 10 cm) tall. The container should be at least 10 inches (about 25 cm) wide and 8 inches (about 20 cm) deep, and the seeds should be planted at a shallow depth, no more than 0.25 of an inch (about 0.6 cm) below the surface. Before planting in this fashion, the seeds should be mixed with sand, using three parts sand to one part seed, so that the seeds will be more evenly dispersed. Once the seeds are started in a container, the cilantro should not be transplanted into an outdoor garden as this might cause the plants to mature and flower to soon, called bolting.
The soil in which the cilantro seeds are placed should be moistened before planting and should kept moist but not saturated. Watering should be done using a light mist so as not to displace the seeds. Cilantro seeds do well when the temperature of the soil does not exceed 75°F (about 24°C).
Early spring and late fall are usually the preferred times to plant cilantro seeds. The seeds thrive well in cooler temperatures and will tend to germinate and mature too quickly in hot weather. They also prefer full sun but can be placed in partial shade for a short time if the temperatures get too warm. In order to maintain a continuous crop of cilantro to harvest, new seeds should be planted every three to five weeks. Cilantro plants are self-seeding, and if some of the plants are allowed to mature and bolt, they will reseed the area themselves, although this technique could lead to overcrowding and soil depletion.