Garlic is a crop that takes just 10 minutes to harvest. If you have already completed a Garlic Collection before receiving this quest, it does not count. You will need to complete another Garlic Collection after receiving this quest.
Garlic only takes 10 minutes to harvest, and will drop an item from the Garlic Collection almost every time, so this collection should be quite easy to obtain.
You will receive 183 Silver Coins for completing the collection, as well as the quest rewards.