A bit more on saving seed from You Grow Girl site.
- Harvesting Seeds
- If this will be your first time saving seeds, start out with some easy plants that flawlessly produce seeds without any intervention. Annuals such as cosmos, marigolds, pansies, corn flowers and many others are some of the easiest. Collect seeds from the highest quality and healthiest plants. A good specimen is disease and pest free, has bright foliage and flowers, and grows vigorously. Under usual circumstances snipping flower heads off after they are spent (deadheading) is crucial to encouraging a plant to continue producing new flowers. To save seed, leave the flowers on the stem after the flower dies off instead. That way, the plant will start putting its resources into producing seed instead of new flowers.
Before long a seedpod will replace the spent flower. Don't remove the seed head right away: leave it on the stems as long as possible, letting it ripen within the pod. Seeds are generally ready when the pod turns brown, dries out or cracks open. If you notice that the seed pod is prone to cracking open on it's own (snapdragons, violas, pansies), attach a lunch-sized paper bag around it using an elastic or string, catching the seeds as they fall. When the seeds are fully ripe, cut the stem at the base of the plant and shake the seed head inside the bag to dislodge the seeds from the casing. If some seeds are lost to the soil they will come up on their own next year. This is called self-seeding, and many annuals reproduce themselves this way.
If the seed heads are not fully dry and ripe when you cut them off, either hang the stems (with the seed cases) or lay them flat to dry on a newspaper or paper towel pad away from direct light. Make sure that all seeds are completely dry before removing them from the pods: if you package them before they are fully dry they will go moldy in storage. This is the simplest way; it's easier to dry the whole seed head then a bunch of loose seeds. When the pod is dry, extract the seeds by carefully crushing or breaking open the seedpods. Separate crushed debris from the seeds by sifting everything through a fine mesh screen. The debris will fall through and the seeds will remain on top of the screen. Some seeds such as those from marigolds or black-eyed susans can simply be pulled from the seed head.
Seeds from fruits and vegetables should be collected when plants are at their peak, before they are over-ripe and decay has set in. Some vegetables such as beans are the exception and should be harvested when the pods are dry. Seeds from most fruits and vegetables are incased inside a wet environment (the part usually eaten). In the case of very wet pulp such as tomatoes, the seeds can be washed from the pulp and then laid out to dry on newspaper or a screen. The same can be done with pumpkins, squash and other soft pulp vegetables. In the case of harder pulp fruits and vegetables they are simply opened up and the seeds removed manually.