Giant crops can grow from cauliflower, melon, or pumpkin when planted in a 3×3 grid of the same crop. All nine crops must be fully grown, and the center crop needs to be watered for the chance of a giant crop to appear.
Once the center crop is fully grown and watered, you don’t need to water the rest of the grid again. The giant crop may appear the next morning if conditions are right.
Unlike regular crops, giant crops do not die when the season changes. They will stay on your farm until you choose to harvest them.
To harvest a giant crop, use an axe. This will break the crop and give you 15 to 21 items of that crop, all normal quality.
Keep in mind, the soil under a giant crop may become untilled after harvesting. This means any fertilizer used on those tiles will be lost.
This method takes patience, but the reward is worth it for a busy farmer looking to maximize each harvest.