Don't forget to try to save seeds from the plants you grow. Send saved seeds back to the library or give them to a friend so someone else can give it a try. Or keep them and sustainably grow your own plants!
Below is some info about how to save seeds. Most of this information can be found in "The Complete Guide to Saving Seeds"
Saving seed from fruit can be easy and straight forward.
Beans: Leave uneaten bean pods to dry and cure, then shell by hand. Store seeds in a cool environment.
Pepper fruit is a podlike berry. Leave pepper on plant until wrinkly, scrape out seeds and let them dry in a worm spot out of direct sunlight.
Tomatoes: You can allow the fruit to sit after harvest until it softens and becomes very mushy, or even begins to rot, then squeeze the seeds out of the fruit. Or immediately after harvest, squeeze the pulp and seeds from the fruit into a container, add a small amount of water, and let ferment several days at or below 70 degrees Fahrenheit, stirring several times a day to speed fermentation, The fermentation process, which takes about 4 days, protects against seedborne bacterial canker. Nonviable seeds will float, while seeds having the best chance of being viable will sink. Pour off the water and the floating seeds.
Milkweed seeds can be found in a pod-like structure that appears on the plant in the fall.
Allow pod to dry on plant until they begin to ripen and split. Dry the fruits further on a screen, then open by hand and remove the seeds. Each seed will have attached a long tuft of "silk."
Swiss Chard is a biennial, meaning that it will not set seed until the second year of growth. At seed maturity, plants of this species take up a fair amount of garden real estate. A benefit to growing Swiss chard for seed is that you can lightly harvest the plants in their first season for food, and then let them overwinter and harvest the seeds the next year.
Once seeds start ripening, there will almost always be a mixture of mature and immature seeds on plants. Harvesting when approximately two-thirds of the seeds are brown is recommended. Depending on the scale of seed collection, individual seedstalks can be cut or entire plants can be pulled from the garden and moved to a place where they can continue drying. Depending on the percentage of ripe seeds at harvest, 7 to 14 days should be a sufficient drying period.
Carrots are biennial which means they have a two year life cycle and require a cold period, usually over winter, to induce flowering.
In northern areas, plant carrots in May and June. Carefully dig the stecklings (first year roots) in mid-October and remove the tops, leaving 1-2 inches above the roots/soil line. Store in a cool, dark humid location, such as in damp sawdust or sand or in barrels with layers of straw between the roots. In areas with mild winters, you can plant the carrot seeds in midsummer and overwinter in place, covered with mulch. If stecklings have been stored, replant sound ones in early to mid-spring slightly deeper than they were growing previously, about 2 feel apart in a row. If roots overwintered in the garden, be sure to thin them to this spacing. The plants will resume growth and send up stalks using the sugars stored in their roots.
It may also be possible to grow carrot flowers from carrot tops. Place a one inch carrot top piece in water. Once it develops roots it can be planted in soil.
Carrots will cross pollinate with other varieties from the Apiaceae (parsley family), so if you'd like to avoid creating hybrid varieties, isolate flowering carrots of the same species or subspecies.
Harvest carrot flowers (umbel type) when most umbellets are brown.
Bag the flower stock to catch the seeds as they dry and drop.
Cure seed for 4 to 5 days in hot, dry environments, or for at least 2 weeks in more humid places.
Radishes produce seed pods about 1-3 inches long.
Collect pods individually when brown and allow them to dry. Once dry, separate seeds from any extra plant material.
The seed saving process is pretty similar for the following flowering herbs.
With Basil, Cilantro, Dill, Parsley, and Thyme, collect flowers as they dry or tie a paper bag over the flowers and wait for them to dry in the bag, as many flowers will shatter. You can use a screen to dry the flowers further and rub out the seeds, making sure all plant material has been removed.
Arugula plant will send up stalks when ready to seed. After the plant flowers, it will produce elongated seed pods. When the pods began to dry and brown, remove them from the plant. Allow them to dry until the pods become very brittle. Remove the seeds, discard or compost the pods. Store the seeds in a cool environment.
Harvest sunflower heads when the seeds are dark colored and begin to rub off easily.
Hang the sunflower heads upside down and dry for 2 or 3 weeks. Dry the seeds on a screen, then store dried in sealed containers.
After the flowers fade, pointed seed pods will develop that mature from green to brown. When ripe, they will split open at the top to reveal the tiny brown seeds. Shake the open pods over a container to remove the seed. Store the cleaned seed in a cool, dry place.
The New Jersey Tea plant spreads its seeds by exploding them our of their pods, making harvesting a challenge. Keep a close watch on the heads, since they explode soon after they turn a dark color. When the seed head turns nearly black, remove them and spread them out to dry. A light cover of some kind may be necessary, since the seed heads may explode and release their seeds as they dry. Separate the seeds from their pods and store the cleaned seed in a cool, dry place.
Purslane produces yellow flowers that bloom for a short time. Then they form a small green fruit fruit in the center of the leaves, open the fruit to find purslane's seeds. More information can be found in the link below.