Saving seeds of most hybrid annuals is a thankless task because not all of next year's flowers will be up to the standards of this year's cultivars; each year they will either get smaller in size or lose much of their color, or both. And it's impossible to tell which seedlings will be acceptable until they bloom (although some cultivars, such as Nicotiana "Lime Green," will flower true-to-type).
Most of the annual seeds can be gathered, placed in paper envelopes, carefully labeled, then stored in a cool, dry, dark place until they are needed the following spring.
All the annual ornamental grasses are perfect for seed-saving, as well as bishop's weed, winged everlasting, borage, creeping zinnia, tithonia, Johnny-jump-up, bells-of-Ireland, most tree mallows, California poppy, and starflower.
The end of summer is the time to watch for ripening seedpods to be dried for winter bouquets. It's the time of the year when flowers seem to sense the approach of cool weather and often burst forth with a last round of bloom. The colors seem brighter against the sharp blue skies that appear as temperatures fall, and the air trades that misty softness of summer for the crystalline clarity of autumn.
As the days grow shorter you will be surprised by the strength of some of your annuals. The leaves of the various strawflowers (many have their origins in Australia) may shrivel with the increasing cold of autumn, but their stiff petals of bright orange, red, yellow, or white resist the advances of frost, continuing to glow in the morning sun of early fall.
The flowers of the poppy may be gone, but the marvelous seedpods are still there. Fall brings out the glorious colors of the flowering cabbages and kales, plants that need the nip of frost not only to grow but also for their colored leaves to shine.
Then there are the pansies; they'll bloom all winter in areas of the country where winters are mild, but will even persist in northern gardens until almost the end of the year, or until snows get too deep for casual walks to the garden. Sweet alyssum, too, will keep flowering far into fall.
This is the time of the year to think about moving some of the geraniums (Pelargonium spp.) into pots and taking them indoors to a sunny windowsill for winter bloom. Some annuals, such as bedding begonias or ageratums, can be dug up and placed in small pots, where they will continue to produce flowers until the very short days of December.
Polka-dot plants(Hypoestes phyllostochya) are really tropical perennials and are easily moved to indoor pots for the winter. Even marigolds will fight the advancing seasons and bring a spot of gold to the living room.