John Gill Commentary Isaiah 37:30

"And this shall be the sign unto thee: ye shall eat this year that which groweth of itself, and in the second year that which springeth of the same; and in the third year sow ye, and reap, and plant vineyards, and eat the fruit thereof." — Isaiah 37:30 (ASV)

And this shall be a sign to you
Not to Sennacherib, but to Hezekiah; for here the Lord turns from the former, and directs his speech to him, in order to comfort him under the dreadful apprehensions he had of the Assyrian monarch, and his army; assuring him of deliverance; giving him a sign or token of it. This sign was a wonder, as the word sometimes signifies, and was no less marvellous than the deliverance itself.

you shall eat this year such as grows of itself: and the second year
that which springs of the same: and in the third year you sow, and
reap and plant vineyards, and eat the fruit of it :
All which was very wonderful. Either through the invasion of the land and the siege of the city, they could not till their land as they had used to do, or what was upon it was destroyed or eaten up by the Assyrian army. Yet, through the wonderful providence of God, the earth of its own accord yielded that very year a sufficiency for them. Though the second year was, as it is thought, a sabbatical year, when the land had rest and by the law was not to be tilled, yet it also produced of itself what was sufficient for their support. Then the third year, being entirely free from the enemy and all fears of his return, they went about their business as formerly, to sowing and reaping corn, and planting vineyards, and enjoying the fruit of their labours.

All which falling out according to this prediction, must greatly confirm the mind of Hezekiah, and make him easy as to any future attempt upon him he might fear.

The Vulgate Latin version renders the second clause, "you shall eat apples the second year"; and so Symmachus, but without foundation.