A method for minor garbage collection in a multitasking environment involves marking cards as clean, where the cards designate ranges of memory locations in a shared older generation. The method further involves marking a card as dirty when a reference field of an object within the card is modified, where a memory location of the reference field is designated by the card, where the reference field references a live young object in a task-specific young generation, and where the task-specific young generation is associated with a first task. The method further involves marking the card as single-dirty when the card only includes roots of live young objects in the task-specific young generation, and optimizing task-specific minor garbage collection for a second task by skipping the card when the card is marked as single-dirty.