The process required to save seeds varies from one plant to another. In most cases, you will need to wait until the end of the growing season for the seeds to fully mature. At this time, you can begin the process of collecting, cleaning, and storing the seeds for future planting.
Begin by identifying the fruits, vegetables, or flowers from which you want to save seeds. If you have more than one of the same type of plant, identify the healthiest looking plant during the growing season. Harvest seeds from your most successful plants to increase the chances of growing equally healthy plants in the future.
For most plants, you need to leave the vegetable, fruit, or flower on the plant as long as possible to allow plenty of time for the seeds to mature. To save seeds from peas, beans, squash, cucumber, and eggplants, for example, you should leave the vegetable on the plant until it is past the ripe stage where you would eat it. If the plant has pods, they will rattle when the seeds are ready to be harvested. Squash should be left until they are very hard, and cucumbers should remain on the plant until they begin to get mushy.
When the seeds are ready for harvesting, you should gently remove them from the fruit or vegetable. If the seeds are wet from the moist flesh of the fruit or vegetable, you must clean and dry them. Place the seeds in a jar filled with clean water to rinse them. The viable seeds will sink to the bottom. Discard any seeds that float to the top.
Once the seeds have been rinsed clean, lay them out in a single layer on a clean screen to dry. Set the seeds in a cool, shady spot. If they become too warm or are left in direct sunlight, they may sustain damage.
Some seeds, such as tomato seeds, need to ferment before they are cleaned and dried. Leave these seeds in a clean jar with the pulp of the fruit and a small amount of water. Stir several times a day. After about three days, the seeds will have completely separated with the viable seeds on the bottom of the jar and bad seeds floating on top. Discard the pulp and bad seeds and proceed to clean and dry the good seeds as described above.
Once the seeds you have collected are dried, they are ready for storage. With some vegetables and most flowers, the seeds will already be dry when your remove them from the plant. Store the prepared seeds in paper envelopes or clean glass jars. Label them with the type of plant as well as the year. In many cases, you can save seeds for two or three years. For the best results, however, you should plant your saved seeds the following season.