Coriander seeds will need to be dried in order to be planted to propagate new herbs next year. Therefore, when you are planning how to harvest coriander seeds for planting, it pays to leave seeds on the plant for as long as possible. Drying them naturally by spreading them out, or hanging them as described above, will help them fall from the stalk easily and leave them ready to be planted. Dried and stored coriander seeds can last for years and be there ready for when it is time to sow cilantro from spring to fall.