Once a watermelon has been cut open the watermelon will only last for around 3 to 5 days before it goes bad.
If you cut open a watermelon make sure to refrigerate it and if possible wrap the cut open watermelon in some plastic wrap.
Wrapping the watermelon in plastic wrap will help seal in moisture to prevent the watermelon from shriveling up and drying out.
A watermelon that has not been cut open will last for up to 2 weeks before it goes bad.
If you have watermelons that are not cut open they will last for 2 weeks and should be eaten within 2 weeks of buying or picking them from the garden.
Once cut open the watermelon should be eaten within 5 days before it goes bad.