Collecting seed from annual evening stock (Matthiola longipetala or Matthiola bicornis) is an interesting experiment in plant genetics with the side benefit of saving on your garden budget. The sweetly scented flowers, commonly purple, pink or white with single or double petals, don't often come true from seed the next year, even when they aren't hybrids and you grow only one variety of the self-pollinating plants. White-flowered plants tend to revert back to pink or purple and double-flowered varieties revert to single, while seed from single-flowered stock can yield plants with double-flowered blooms. Whatever your results, the 1-foot flowers look and smell wonderful in the garden, and saving the seed is a snap.
Watch for 2-inch-long, cylindrical seed pods, called siliques, to form on your evening stock as flowers fade and petals drop off.
Clip off the faded flower stalks with the pods attached as the siliques turn from green to yellow -- they split down the center and disburse the 50 to 60 seeds inside when they turn brown. Choose stalks from only the healthiest plants.
Place the seeds stalks into brown paper bags -- loosely so air flows around the plant material --- and place the bags in a warm, dry area protected from the weather until the siliques split open.
Swish the stalks back and forth against the sides of the bag, or run your hand over the open pods to dislodge all seeds into the bag.
Pour the seeds into a paper envelope. Store the envelope in a jar and seal the lid. Store the jar in a cool, dry place until it is time for planting. Seeds can store for about 12 months without losing any quality.