John Rolfe saved the Jamestown colony by experimenting with the growing of tobacco. Up until this time, the colonists had tried all kinds of trades and manufactures to make a profit, without much success. It was only after Rolfe started growing tobacco, which could then be exported to England, that the colonial economy began to improve.
Jamestown was primarily an economic venture, and as such, it was expected to turn a profit. It wasn't enough that the English should establish a colony in Virginia; they also had to make it pay. Thanks to Rolfe's innovations, it did just that. In a short period of time, the tobacco crop became a major source of wealth for the colony. By 1617, tobacco exports to England totaled somewhere in the region of £20,000: a phenomenal sum of money at that time. Within twelve years, that figure would be up to an astronomical £500,000, putting Jamestown's economy on a firm financial basis.