This page or section contains unmarked spoilers from update 1.6 of Stardew Valley. Players may want to avoid or be cautious toward reading this article/section.
Mushroom Log
Grows mushrooms every so often. The more wild trees are nearby, the better it works.
The Mushroom Log produces mushrooms every 4 days, rainy days will cause this to take a day less.
Quantity
The quantity of mushrooms produced increases with the amount of wild trees in the 7×7 square around the log. The amount of mushrooms generated, limited to between 1 and 5, is calculated by finding the number of nearby trees and multiplying this by a random number between 0.5 and 1.5.[1] Therefore, the number of nearby trees needed to always gain the maximum amount of 5 is 10.
Type
The type of mushrooms produced depends on the type of trees nearby. The game code creates a list of possible mushrooms based on nearby trees, and then selects one at random from that list.
First the game finds how many trees are in the 7×7 square around it. That number is multiplied by 3/4 and that many mushrooms (at least one) are added to the list with a distribution of 5% purple, 14.25% red and 80.75% common.
Then, one more mushroom is added for each mature tree. If the tree is a Oak Tree then the mushroom added will always be a Morel. The same goes for Pine Tree with Chanterelle, and for Mystic Tree with Purple Mushroom. Maple Trees have a 10% chance to give a Purple Mushroom and a 90% chance to give a Red Mushroom. If the mature tree is none of these types, the same distribution as in step 1 is used.
Finally, a random mushroom is chosen from that list to generate.[1]
Quality
The quality of the mushrooms produced can vary, but is not affected by the Botanist Perk. Instead, the quality is calculated based on the number of nearby trees, and how many of them have moss on them. Each nearby tree is counted, with mossy trees counted twice This number is then divided by 40 and is used as the chance for the quality to upgrade. This chance occurs repeatedly until it fails or reaches iridium quality.[1] So for example if the count is 20 then the chance is 0.5, meaning there is a 50% chance of regular quality, a 25% chance of silver quality, a 12.5% chance of gold quality, and a 12.5% chance of iridium quality. If the count is 40, 5 mushrooms of iridium quality are guaranteed.