Matthew 13:26,27

‘But when the blade sprang up and brought forth fruit, then appeared the tares (darnel) also. And the servants of the householder came and said to him, “Sir, did you not sow good seed in your field? From where then has it tares (darnel)?” '

For quite some time wheat and darnel grew together with no differentiation made between them, but when the wheat began to come into ear the difference became clear, so that the servants working in the field inevitably noticed it. This puzzled them. These were no ordinary weeds. So where had they come from? Who had sown them? They reported it back to the householder.

Note how this time little attention is paid to the period of growth. This is in direct contrast with the parable of the sower. Thus it serves to emphasise how important the period of growth was in that parable.