Harvesting and saving basil seeds is a relatively easy process that can be done in just a few steps:
Wait until the basil flowers have dried out and turned brown. This is a sign that the seeds are ready to be harvested.
Cut the flower stalks off the basil plant and place them in a paper bag. Be sure to label the bag with the date and the variety of basil.
Hang the bag upside down in a warm, dry place for a few weeks. This will allow the seeds to fully dry out and separate from the flowers.
Once the seeds have fully dried, gently shake the bag to separate the seeds from the flowers.
Remove the flower debris and other plant material from the bag, and transfer the seeds to an airtight container.
Label the container with the date and variety of basil, and store it in a cool, dry place until you're ready to plant the seeds.
When planting basil seeds, it's important to keep in mind that they have a relatively short shelf life. For best results, it's recommended to plant the seeds within 1-2 years of harvesting them. To ensure germination, soak the seeds in warm water for a few hours before planting, and plant them in well-draining soil in a warm, sunny location.
This can be a tricky bit, taking out the big stalks is okay but separating tiny seeds from broken up flower debris is tiresome. I don't usually bother too much, the debris helps to spread the fine seed when you sow, I have never bothered soaking the seed either, I suppose they might germinate better, but I get so many seeds even if germination rates are low I still have plenty of plants.