“…The kingdom of heaven is like a mustard seed, which a man took and sowed in his field, which indeed is the least of all the seeds; but when it is grown it is greater than the herbs and becomes a tree, so that the birds of the air come and nest in its branches.“
(Mathew 13, 31-32)
Seeds of mustard and a mustard flower: 
Many people that read the verse above from Mathew, tend to think that the mustard is a big tree.
Well, this is not the case. In Israel the mustard is a very common wild weed that grows almost everywhere except for the desert. It has yellow flowers and a strong odor of mustard. During the spring it paints the fields with a strong color.
Wild Mustard field in Golan heights:
The mustard is very known in Israel as a herb and a medicine. People used in the time of Yeshua, and until today it is used by the local people as a vegetable and as a medicine.
Mustard condiment is made from the seeds. 
So why does Yeshua uses the mustard in his parable?
The reason is that the mustard weed grows very fast: It sprouts in the beginning of the winter, and by the end of the spring it gets to be higher than the height of a person. In the summer the weed dries and becomes a thorn bush.
Small birds use the mustard weed to build their nests.
A bird (bunting) on a dry mustard in Golan Heights in the autumn: 
A mustard stem is used for a crown:
Ran Silberman 
Thank you very much for this teaching about the mustard seed
God bless