Some people can forage plums, but I’ve never been lucky enough to see a tree to forage from. I used plums from our little trees to make 5 jars of delicious jam. You can use some cooking apples in with the plums if you don’t have many. Cooking apples have a good amount of pectin which is the thing that makes jam set. If you can get some un-ripe plums mixed in with your fruit, they have more pectin too.