Finding and collecting seeds from plants after they've flowered doesn't require lots of intricate botanical knowledge. If you've never collected seeds before, you'll be surprised at what you can find once you start looking. These tips will get you started, but the best way to learn is just by doing. Get out into the garden and investigate the spent, dried blooms on the plants. You'll find the seeds!
The ovary where seeds form is generally found at the base of the flower, so if you remember how the plant looked when it was blooming, you'll have a good idea of where to look for the seeds. Seeds vary a lot in appearance. Some are large and crinkled, some are round and shiny, some are like dust. It can be confusing at first, but once you learn to recognize the seeds of one or two plants, you'll get the hang of figuring out where the seeds are on other plants.
When you're poking around at plant parts, looking for seeds, remember that the seeds will usually be harder, often darker, and more uniform in appearance than the surrounding bits of chaff and dried leaves. On most plants, you'll want to wait until the seed stems are turning dry and brown before collecting seeds, or the seeds won't yet be mature. Immature seeds are often green, with a soft coat that you can dent with your fingernail.
Some plants tend to drop their seeds before you can harvest them. In those cases, you might want to bag the developing seedheads. Fabric mesh wedding favor bags are inexpensive and work well for this purpose. With tiny seeds that are easily lost, I like to snip off the seedheads into a paper bag or other container. A little shaking will generally drop the seeds to the bottom of the bag for easy separation from the snipped stems and spent blooms.
Hybrid plants, created by crossing one variety with another, won't generally come true from seed. Some hybrids may be sterile and not produce seeds, or the seeds might not sprout. If you're not sure if a plant is hybrid or "open pollinated," whether to collect seeds from it or buy seeds instead depends on how disappointed you'd be if it didn't work out. Especially with seeds I'm collecting for winter sowing, where little effort is needed to try starting them, I often figure "nothing ventured, nothing gained."
From dandelions to castor beans, plants have their own unique ways of forming and dispersing seeds. Looking at some examples will give you an idea of where you'll find seeds on some common garden plants.
Spikes of little flowers can turn into stems of little seed pods.
Basil flowers in this fashion, and I described collecting and de-chaffing basil seeds in detail in this article. The same methods can be used for sages (Salvia), beardstongue (Penstemon), toadflax (Linaria), anise hyssop (Agastache), and speedwell (Veronica). Just strip some remnants off a dried stem and crush them in your hand, then look closely to see if you can find seeds. Seeds will often be tiny, even dust-like. If you're not sure but want to try anyway, just dry, save, and sow it, chaff and all.
Big flowers often form central seedheads
Sunflowers (Helianthus annuus) are the most obvious example, and their seeds are easy to recognize, with their dark or striped hard shells at maturity.
Coneflowers (Echinacea), black-eyed susans (Rudbeckia), yellow ox-eye (Heliopsis helianthoides), and blanket flowers (Gaillardia) have very different looking seeds, but they all form in a cluster at the center of the flower petals.
Some flowers produce pods filled with small seeds.
The upright, vase-shaped seed pods of columbines (Aquilegia) and rose campion (Lychnis coronaria) will spill a wealth of round, dark seeds into your hand.
Crushing a round seed pod from a petunia or toadflax plant releases dozens of tiny seeds.
Marigolds (Tagetes) leave behind papery sheaths filled with what seems at first to be fine dried straw, until you pull the sheath away and see the dark seed at the base of each shaft.
Some flowers produce larger seeds.
If you know where the flowers used to be, look for some sort of seed-containing structure there on the plant. Runner beans (Phaseolus coccineus) produce fat pods containing huge seeds, viable when the pods are dry and the beans are hard. Morning Glories and other Ipomoea species produce papery round pods containing several chunky seeds that have a hard, black coat when mature. Castor Beans (Ricinus communis) are found within the sections of enormous round, hairy pods.
Some DG PlantFiles entries include seed photos, and there are other good seed identification resources online, such as TheSeedSite. DG subscribers can turn to the Saving Seeds forum and other discussion forums for help with finding and harvesting seeds from different types of plants. Once you start saving seeds from a few garden favorites, you may find yourself looking for seeds everywhere. The art and sport of seed snatchin' is an honored tradition among many DGers.
Collecting your own seeds is easy and can become downright addictive. It's a great way to get lots of seeds for sharing, trading, and sowing! Whether you start seeds inside or winter sow them, it's fun to have a fat seed stash to choose from when it's time to start planting.
Get out into the garden and shake down your plants for some seeds!
Photos in the article were taken by me in my garden. Move your mouse over the images for additional information.
Understanding the botany of flowers can give you an even better idea of where to look for seeds, so please check out LariAnn's excellent and clearly-written
"Botany for Gardeners" articles.