FusionTheism: No wheat at all for 1900 or 1800 years would not fit to the parable, because wheat grows allways togehter with weed, so if weed grows alone that would be a misuse of the parable.
But the parable cant be used as timeline measure.
The begin of the parable "with the coming of the kingdom of heavens is similar to"...does not offer a timeline of happenings within the history. This expression was used by jewish rabbis and scribes in the 1st century often to tell aboout right behaviour and insight into the faith at the present time, that not a prophesy about what happens later. "It is like in this story..." In Mark 4,26-29 too the author of the gospel does not tell something about the ongoing growth of the church, of a process in history, because the farmer is mentioned only in the beginning and in the end. In the meantime the farmer can do nothing, only sleep and wait and get up in the morning. Automatical completley without the farmer the harvest ist done, a harvest that is described by Joel in 4,13, as Gods impact, than Gods time is here. So in the parables of sowing and harvesting and likewise of the growing wheat the process of growing is not important. #
It simple tells of the the wondeful intervention of God, who lets grow the semen after it is led into the ground, of the wonder that through gods intervention the fruit grows and new life rises. No man could hinder God or speed up this. With the kingdom of God is is likewise.. we can trust to that Gods sets begin and end of the harvest.
Not a churchhistory of growing, building activities, growing number of church-buildings, or human activities like projects e.g. is described, but the contrast between sowing and harvesting as a divine wonder. That was typical jewish thinking of that time period, that the sowing and harvesting are a divine wonder.
Likewises we can trust in the Kingdom of God is a divine wonder. "Its like in this story..." Nothing more can be read out of the parable. As already mentioned the wheat and weed parable likewise teaches that we can trust in the wonder that God will somehow protect the wheat among the weed.
My verdict is that the wonder of the wheat among the weed is a reference to Gods intervention, but no reference to an intervention of the faithful servant or the anointed in the harvesting, that they should burn the weed.