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How can I get more unwither
There are lots of chances to get unwither spray: leveling up prize on newer farms, build and harvest the Big Windmill, harvest the Garden on Farmer’s Square, the weekly leaderboards, some quests, build and harvest the Sporty Doghouse, a prize when playing the Time Machine, Daily Delights prize and the Community Goals on each new farm.
The most reliable source (the rest are a chance of getting) is the Garden on Farmer’s Square which can be harvested several times a day but it is also the most work to level up.