ANSWER: To sow a seed simply means to plant it. The word of God uses this as a metaphor to describe the concept of working to achieve something positive. The Bible often uses symbolism associated with agricultural production because it was such an important part of ancient people's daily life, unlike the majority of people today.
In one of Jesus' parables he uses the analogy of someone sowing seeds, and what can happen to the seeds afterwards, to teach about the different responses people will have regarding the gospel message (Luke 8:5 - 15).
Seed time, in relation to firstfruits, refers to the time when the environment, temperature and season are appropriate for the placing of seeds in the ground for their best success of growing.
Growing up on a farm we spoke of seedtime as the time when the earth was warm enough and moist enough from the early spring rains to best guarantee the "sprouting" of the seed once it was placed in the ground. Otherwise, it would simply lie buried in the soil and die.
Springtime is the time of seeds. It is the time when life springs forth from the earth. We could associate "seed time" with the time of planting (Isaiah 60:21, 61:3).
Spiritually, we could say that when God places his Holy Spirit in us at the time of our repentance and baptism, it is a spiritual seed, the "beginning" of spiritual life within us. However, we can't let that "seed" just sit there and not grow, or it will die. We must water the "seed" of the Holy Spirit with continued bible study and prayer. We must put into practice every word of the teachings of the entire Bible to allow the Holy Spirit to grow in us.