It is a great feeling to go out into the garden and pick fresh plums off the tree. But once they have been harvested, you will need to act quickly if you wish to preserve them for longer than a week.  Plums can be kept in the refrigerator for up to one week but at room temperature for no more than 3 days. Therefore, it is best to store them in some form that will maintain their goodness for as long as possible. This can range from making jams and marmalade or using them in recipes right away.