Prepare the Plums: Start by washing and pitting the wild plums. You can leave the skins on for extra flavor.
Combine Ingredients: In a large saucepan, combine the plums, sugar, lemon juice, and water. Stir gently to mix.
Cooking: Bring the mixture to a boil over medium-high heat. Stir frequently to prevent sticking. Reduce the heat and let it simmer for about 45 minutes until the jam thickens. Skim off any foam that forms on the surface.
Test for Doneness: To check if the jam is ready, place a small amount on a cold plate. If it wrinkles when touched, it's done. If not, continue cooking for a few more minutes.
Canning: Pour the hot jam into sterilized canning jars, leaving about 1/4-inch headspace. Seal the jars with lids.
Water Bath Canning: Place the filled jars in a water bath canner. Ensure they're covered with water and boil for 10-15 minutes.
Cool and Store: Remove the jars, let them cool, and check for proper seals. Store in a cool, dark place.