The Legend of Zelda: Oracle of Ages/Gasha Seeds

In-game hints
"I am Bipin, the expert arborist! I know plenty about trees. Now let me tell you something!"
 * 1) "My experience holds that planting Gasha seeds in strange spots produces more rare and unusual results!"
 * 2) "Finding new places to plant Gasha seeds and finding secret stairways seems to be good for Gasha nuts."
 * 3) "A traveler once told me the time it takes for a planted Gasha seed to mature into a tree is related to how many monster you slay. Could this be true?"
 * 4) "The contents of a Gasha nut depend on where the seed was planted. If you find a good spot, tell me!"
 * 5) "Inside a Gasha nut? More than anything, you find magic rings, but sometimes you find Rupees or hearts."
 * 6) "I have heard that a nut's contents depend on the actions of the planter. The more he travels and the more beasts he slays, the better his nut will do!"
 * 7) "And helping those in need is good for Gasha nuts."

Gasha mechanics
There are 16 soft soil locations and more than 32 Gasha seeds in the game. 28 different magic rings can be found inside Gasha nuts (or from Maple); in particular, 16 rings can only be obtained from Gasha nuts (or from Maple).

Plant a Gasha seed every time you find a soft soil patch. Come back to the grown Gasha tree after you cleared three/four dungeons. Get the Gasha nut, and plant a new Gasha seed straight away (because a Gasha tree withers as soon as its nut is taken).

Notable rings:
 * The Discovery ring helps finding soft soil (found in chapter 1 dungeon, ../Spirit's Grave/);
 * The Gasha ring helps getting better rings (randomly obtained from Gasha nuts, Maple, or Blue Snake).

Locations of Gasha seeds and soft soil patches
In the following table, locations where Gasha seeds can be obtained repeatedly are highlighted in green. Ch. stands for Chapter; LG stands for "Linked game". The Rar column specifies the rarity of rings that can be obtained from each soft soil patch (1 = common, 5 = rare).

Credit: Table based on information by DBM11085.