How Long Is Fertilizer Effective In The Stardew Valley Greenhouse?

Fertilizer placed in the greenhouse will remain in the soil unless un-tilled by a pickaxe. Crop quality is determined at harvest time, not planting time. Prior to 1.5, fertilizer used in the greenhouse on crops that would mature out of their normal growing season might disappear before harvest and have no effect. Multiple harvest crops and fertilizer will never disappear from the greenhouse unless removed by the player or in the case of fertilized soil as long as the tile does not spend a night unplanted. This is also true on Ginger Island, where there is no seasonal change on the island, making the farming space equivalent to the greenhouse since you can grow whatever you want there.

Speed-Gro/Fertilizers last as long as there is a plant growing (even across seasons) or if the soil remains tilled during a season. Fiber works in the greenhouse but goes away every season change. If you run a Quick-Gro at the top of the month for a repeater-plant, it will start producing earlier. Quality fertilizer is the best in Stardew Valley, as it shaves 25 of the growth time, saving 4 days for plants that take 12 days, like cauliflower.

In the greenhouse, the fertilizer lasts forever, and to get rid of a fertilized spot (to use better fertilizer), you must use your pickaxe to revert it. Once repaired, it can be moved by talking to Robin at the Carpenter’s Shop. The wiki says it wears off after a season, but some players have found that they can re-apply basic or quality fertilizer inside the greenhouse without replanting everything.