Vinca, also known as periwinkle, produces colorful blossoms in the spring. This member of the dogbane family grows between 8 and 18 inches, and forms about a 1-foot-wide plant at maturity. However, a few types of vincas form trailing and twining vines. These annual plants produce blossoms in various shades of peach, red and purple. Although many garden centers sell vinca seeds for planting, many gardeners prefer to gather their own seeds from existing plants at the end of each growing season.
Check your mature vinca plants regularly after blossoms begin to droop and fade. Look for the appearance of seedpods replacing the spent blooms. Cut back on the frequency of watering sessions as the blossoms begin to fade and seedpods appear.
Test the seedpods for maturity by gently shaking them on the vine. Begin harvesting the seedpods before the snowfall. Although some plants drop their seeds in the fall, mature seedpods often remain on the vinca plant well into the winter months. Listen for a rattling noise when shaking the seedpod. A dry outer pod that makes a slight rattling noise when shaken indicates seed maturity.
Pluck or snip the mature seedpods from the parent plant by gently pulling at the base of the pod with your fingers, or snipping away pods with a sharp pair of scissors. Drop harvested pods into a paper bag after removing from the parent plant.
Sort and clean your vinca seeds. Sprinkle the seedpods on a clean piece of newspaper. Remove any wilted or diseased pods. Toss out any debris or bugs found amongst the healthy seedpods. Make sure all your pods are dry before storing for the winter. Allow green or soft pods to set out in the sunlight until thoroughly dry.
Pop open dried seedpods to remove individual seeds from within the pods. Check the health of the individual seeds by looking for uniform color and shape. Toss out any deformed or stunted seeds from your collection.
Package your dry seeds in a dark, dry container, such as a paper bag or thick envelope. Write the name of the seeds and the date harvested on the outside of the container. Place the container in a cool dark area until ready for planting.