Chia may have gained popularity as a "pet" in the 1980s, but chia's most important legacy is its seeds. Once a major food source of the Aztecs, chia seeds are a significant source of omega-3 fatty acids, soluble fiber and a number of other essential nutrients. Once mature, chia sees can be harvested quite easily. In fact, the process has changed little since the time of the Aztecs.
Observe your chia plants for signs that their seeds are ready for harvest. Once the chia's flowers have yellowed and dried in late summer, the seeds should be harvested. And if not gathered soon after that point, they will fall out of the plant and begin to germinate.
Uproot your chia plants. Chia is an annual, so the blades will soon die anyway. Pull the entire plant out of the ground by grasping it at its base and place it in a container.
Grab the chia plant near its base and hit the top of the plant against the inside edge of the container until its seeds fall into the container.
Toss the de-seeded chia plants onto the compost pile.