To change a plants Fertilizer settings go to the plants blueprint so for example the BP_TomatoPlant and select the BP_PlantComponent in the Components panel, then in the Details panel and inside the Plant Settings Category find the Fertilizer category like the image below.
Here you can change this plant’s Fertilizer settings, you can hover your mouse over each settings name to get a tooltip with more info about each setting.
You can enable or disable the Use Fertilizer setting to remove the plants need for Fertilizer.
You can also set the plants Max Fertilizer which is the maximum amount of Fertilizer the plant can store, you can also change the plants Starting Fertilizer which is the amount of Fertilizer the plant begins with when placed or when the game starts.
Fertilizer Usage Time is how often a plant consumes its Fertilizer in seconds and the Fertilizer Amount is the amount of Fertilizer that will be used.
You can enable or disable the Show Fertilizer Usage UI this will remove the Fertilizer usage panel from the plants UI.
You can set the plant to take damage when it has no Fertilizer, this can be enabled or disable using the Use No Fertilizer Damage setting.
No Fertilizer Damage Time controls how often the plant will take damage in seconds and the No Fertilizer Damage is the amount of Damage the plant will take when it has no Fertilizer.
Fertilizer can effect how fast the plant grows and how fast the vegetables grow. This uses the Growth Multiplier setting, if set to 0 having Fertilizer wont effect the plants growth speed, if set to 0.5 the plant will grow 50% faster then its normal speed, this effect stacks with other stats grow multipliers.