1- Save the best seeds
Save the best-quality seeds, from the healthiest, most vigorous plants. Look for seeds that are well-formed and as unblemished as possible, with no obvious signs of infection or pest damage.
2- Lose the moisture
Dry them before storing them.When you store your seeds, they should have the lowest possible moisture content. If not, they will mold or rot. When drying them, put them on a shelf in a well-ventilated room and out of the sunlight. Make sure the airflow reaches the top and bottom of the seeds. I also shake them around every few days, making sure that all the seeds get equal ventilation. Drying for 2 to 3 weeks is ideal.
3- Freeze your seeds
Freezing them kills any insects or diseases in or on the seeds. This is a great option if you aren’t able to plant those seeds the very next year. A well-saved seed can last 5 to 10 years in the freezer.
4- Use airtight containers
You can freeze your seeds in small mason jars, or folded into parchment paper, sealed and stored in ziplock freezer bags.
5- Keep records
Label every jar and parchment envelope with the name of the seed and the date you saved it.
I found that drawing a garden map is very helpful. I write on it what I have planted and where. I also keep a garden diary, writing down what and where I planted something, what bloomed first and when I harvested the vegetables, or wild edibles.
*These tips were partly excerpted from William Woys Weaver’s book Heirloom Vegetable Gardening.