Gather seeds when they're ripe
Collecting seed is a matter of timing. My season begins in May when the Hepatica species ripen and ends in December when the climbing fern (Lygodium palmatum) finally sheds its spores. Generally, seeds of woodland wildflowers tend to ripen within three to six weeks after a plant has flowered. Rather than follow this rule, I recommend using your eyes instead. If a plant produces fleshy fruits, its seeds will be ripe when the fruit begins to color. If a plant’s seeds are enclosed in a woody or papery capsule, wait for it to turn yellow or brown before harvesting its seeds.
While some seeds may continue toripen if picked too soon, it is always best to let them mature on a plant as long as possible. A ripe seed has a coat that is typically some shade of tan, brown, or black. Unripe seed is white or green in color. If you are unsure, try picking the seed in three or fourd batches a week or so apart. This way, you can compare and note when the seed becomes fully ripe.
When collecting, you can also cut seed open to test viability. Ripe seeds should be filled with white material that is some combination of embryo and the food-storing endosperm that often surrounds it. In unripe seed, this material is milky or watery, and the seed coat that surrounds it will be soft and easily compressed. As the seed matures, the inside becomes firmer, like the flesh of coconut, and the seed coat hardens and is not easily crushed between the fingers. At this stage, the seed is ready for harvest even if the seed coat is not quite fully darkened.
Collect seeds once they've ripened. The author collects red baneberry seeds as soon as the fruits begin to color.
A file folder is a handy tool to use when collecting seed. The author shakes out the seed, folds the folder in half, and gives it a shake. The chaff stays in the folder while the seed falls out into an envelope.