Albert Barnes Commentary Matthew 13:26

"But when the blade sprang up and brought forth fruit, then appeared the tares also." — Matthew 13:26 (ASV)

Then appeared the tares also. That is, then the tares were first discovered. They had grown with the wheat, but were so much like it that they were not noticed, until the wheat began to ripen. So, true piety and false hopes are not known by professions, by "blades", and leaves, and flowers, but by the fruit.