Seeing in the distance a fig tree in leaf, he went to find out if it had any fruit.
When he reached it, he found nothing but leaves, because it was not the season for figs.
Then he said to the tree, “May no one ever eat fruit from you again.”
And his disciples heard him say it.
In the morning, as they went along, they saw the fig tree withered from the roots.
Peter remembered and said to Jesus, “Rabbi, look! The fig tree you cursed has withered!”
[Mark 11:12-14, 20-21]
FF Bruce gives this explanation in his book 'Hard Sayings of the Bible':
Was it not unreasonable to curse the tree for being fruitless when,
as Mark expressly says, "it was not the season for figs"?
The problem is most satisfactorily cleared up in a discussion called "The Barren Fig Tree"
published many years ago by W. M. Christie, a Church of Scotland minister in Palestine
under the British mandatory regime.
"Now," wrote Christie, "the facts connected with the fig tree are these.
Toward the end of March the leaves begin to appear, and in about a week the foliage coating is complete. Coincident with [this], and sometimes even before, there appears quite a crop of small knobs, not the real figs, but a kind of early forerunner. They grow to the size of green almonds, in which condition they are eaten by peasants and others when hungry. When they come to their own indefinite maturity they drop off."
These precursors of the true fig are called taqsh in Palestinian Arabic.
Their appearance is a harbinger of the fully formed appearance of the true fig some six weeks later.
So, as Mark says, the time for figs had not yet come.
But if the leaves appear without any taqsh, that is a sign that there will be no figs. Since Jesus found "nothing but leaves" - leaves without any taqsh- he knew that "it was an absolutely hopeless, fruitless fig tree" and said as much.