Interpretation
This parable can be seen as related to the parable of the Sower, although it does not follow that parable immediately. One interpretation is that it serves as a "correction provided for any ancient or modern disciples who might be feeling discouraged with the amount of fruitless labor they had extended toward those" who failed to hear the message of which the parable of the Sower spoke. Even when the farmer sleeps, the Kingdom of God is still growing. Its growth is due to God, not man, and follows its own timetable.
Unlike the parable of the Sower, the seed here seems to represent the Kingdom of God itself. Differences in interpretation result from emphasising different aspects of the parable, such as the seed, the sower, or the earth.
Read more about this topic: Parable Of The Growing Seed