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As the weather gets colder, allowing some basil stems to go to seed will give you the opportunity to plant that basil in the following growing season.
Harvesting is all about timing, seed pod formation, and color and texture changes. Monitor these around late September for October harvesting.
Start harvesting by cutting off the seed heads on a dry and sunny day.
Before removing the seeds allow the seed heads to dry more in a well-ventilated area away from direct sunlight.
Once the seed heads are adequately dried, extract the seeds. You can do this by hand or by shaking the seed pods around in a paper bag.
Store seeds in an airtight glass container or paper envelope. Label the container to ensure no mix ups.
Keep the seeds in a cool, dry, and dark place. Check on them periodically to ensure there are no signs of mold or moisture.