Mark 4:7

“And other fell among the thorns, and the thorns grew up and choked it and it yielded no fruit.”

The farmer could pull up the thorns before sowing but he could not remove the roots of the thorns. Thus both seed and thorns grew together and where there was an abundance of thorn roots the good seed had no chance. As it sought to grow it would be choked. That is why the prophet had warned his listeners, ‘do not sow among thorns' (Jeremiah 4:3). Thus Jesus' hearers already had good grounds for recognising what was intended by His words.