Matthew 13:28-30

Matthew 13:28-30. The servants said unto him, Wilt thou then that we go and gather them up? But he said, Nay; lest while ye gather up the tares, ye root up also the wheat with them. Let both grow together until the harvest: and in the time of harvest I will say to the reapers, Gather ye together first the tares, and bind them in bundles to burn them: but gather the wheat into my barn.

The separation will be more in season, move easily and more accurately done when both shall have been fully developed - when the wheat shall have come to its fullness, and the counterfeit wheat shall have ripened.