Wash the strawberries, blueberries, raspberries, and blackberries thoroughly. Hull and halve the strawberries.
In a large saucepan, add all the mixed berries, granulated sugar, and lemon juice.
Split the vanilla pod lengthwise, scrape out the seeds, and add both the seeds and pod to the saucepan.
Cook the mixture over medium heat, stirring occasionally until the sugar dissolves and the berries release their juices.
Bring the mixture to a boil, then reduce the heat to low and let it simmer for 20-30 minutes, stirring frequently.
Check the jam’s consistency by placing a small spoonful on a chilled plate. If it holds its shape, it’s ready.
Remove the vanilla pod from the saucepan once the jam has thickened to your desired consistency.
Let the jam cool slightly, then transfer it to sterilized jars. Seal the jars and allow them to cool completely before storing.
Store the jam in the refrigerator for up to 2 weeks or freeze for longer storage.