"(The flax and barley were destroyed, since the barley had headed and the flax was in bloom.) The wheat and spelt, however, were not destroyed, because they ripen later.)" NIV translation
The plague of hail was severe but it did not completely ruin all of the crops. This is a picture of God's divine mercy as He could have destroyed all of the plants and animals but He did not. We will see this pattern again as described by John in the Book of Revelation at chapter 8. We are also reminded that this, in fact, is a limited period of mercy on this earth. There is a final judgment where all will stand and answer but, as we see here, it is when the time is ripe.
"Then Moses left Pharaoh and went out of the city. He spread out his hands toward the Lord; the thunder and hail stopped, and the rain no longer poured down on the land." NIV translation
Once again, Moses prayed for the Lord to extend His mercy to Pharaoh and the people of Egypt. Once again, the Lord answered the prayers of Moses and the plague came to an end. In Revelation, we see a reversal of this prayer as the martyred saints plead for God's judgment upon the earth.
"When Pharaoh saw that the rain and hail and thunder had stopped, he sinned again: He and his officials hardened their hearts. So Pharaoh's heart was hard and he would not let the Israelites go, just as the Lord said through Moses." NIV translation
Yet again, Pharaoh's true heart was revealed when the plague ended. There had not been a change of mind and so there would be no change in the course of action which is a sign of true repentance.