The primary Parable of the Sower (as Jesus calls it in Matthew 13:18) is recorded by Matthew, Mark and Luke.  This other one, also called the Parable of the Growing Seed, is only in Mark.  I like to think of it as a further elaboration on the sower’s seed sown on good ground, which “yielded a crop that sprang up, increased and produced: some thirtyfold, some sixty, and some a hundred” (Mark 4:8).

²⁶ And He said, “The kingdom of God is as if a man should scatter seed on the ground, ²⁷ and should sleep by night and rise by day, and the seed should sprout and grow, he himself does not know how. ²⁸ For the earth yields crops by itself: first the blade, then the head, after that the full grain in the head. ²⁹ But when the grain ripens, immediately