Mark 4:26-34 ESV
And he said, “The kingdom of God is as if a man should scatter seed on the ground. He sleeps and rises night and day, and the seed sprouts and grows; he knows not how. The earth produces by itself, first the blade, then the ear, then the full grain in the ear. But when the grain is ripe, at once he puts in the sickle, because the harvest has come.”
And he said, “With what can we compare the kingdom of God, or what parable shall we use for it? It is like a grain of mustard seed, which, when sown on the ground, is the smallest of all the seeds on earth, yet when it is sown it grows up and becomes larger than all the garden plants and puts out large branches, so that the birds of the air can make nests in its shade.”
With many such parables he spoke the word to them, as they were able to hear it. He did not speak to them without a parable, but privately to his own disciples he explained everything.
ESV: English Standard Version 2016