Enricher

Place on a sprinkler and load with fertilizer to automatically apply it when planting seeds nearby.
Overview
An Enricher is a sprinkler upgrade that automatically applies fertilizer to tiles when seeds are planted. Fertilizer must be loaded into the Enricher before planting for it to work, and it will apply the loaded fertilizer as soon as seeds are placed within the sprinkler’s normal range. The sprinkler does not need to water a tile for the fertilizer to be applied.
Only one fertilizer type can be loaded into an Enricher at a time, and enough units of that fertilizer must be loaded to cover every tile you want affected. For example, an iridium sprinkler covers 24 plantable tiles, so using an Enricher with it requires 24 of the chosen fertilizer to fully cover its range. A sprinkler cannot be equipped with both a 
Enrichers can be purchased from Qi’s Walnut Room for Qi Gems, with four available for purchase there. They can also occasionally be found in the Mines as a special monster drop during Danger In The Deep, or after activating the Shrine of Challenge or the Skull Cavern during the Skull Cavern Invasion quest.
Because fertilizer is never removed from tiles in the 
- An Enricher affects planting, not watering.
- It applies fertilizer automatically when seeds are planted in range.
- One fertilizer type must be loaded at a time.
- It cannot be combined with a Pressure Nozzle on the same sprinkler.
- It is most useful when setting up large new plantings, where applying fertilizer tile by tile would be tedious.
Official description
Place on a sprinkler and load with fertilizer to automatically apply it when planting seeds nearby.