Once you get the Legendary Sword from the bottom of the second mine and unlock the Super Field behind the waterfall, go there in the Fall and plant Yams. Because the Waterfall Field speeds up growth by one day and the Yams regrow every two days, there will be a new harvest every day after the initial harvest.
If you are lucky enough to get the Miracle Gloves from the Harvest Sprite casino, have them equipped when you are going through the mines. Whenever you excavate anything you do not need, such as rubble, toss it immediately so that it is shipped. This is a good method to save the Harvest Sprites unlocked by number of items shipped.
