Albert Barnes Commentary Matthew 13:29

"But he saith, Nay; lest haply while ye gather up the tares, ye root up the wheat with them." — Matthew 13:29 (ASV)

Ye root up also the wheat. They so much resembled the true wheat, that even then it would be difficult to separate them. By gathering them, they would tread down the wheat, loosen and disturb the earth, and greatly injure the crop. In the harvest it could be done without injury.