Stop picking flowers about 8 weeks before your first frost. It takes about 6 weeks for the seed pods to form and mature after pollination.
Gently squeeze the seed pod to check if it’s dry. If it drips, it’s still too young. The pod should begin to turn brown, starting at the tip.
Collect the seed heads and place them on a tray or in an open box to dry completely. Once the pods are fully dry and papery to the touch, break them open and separate the black seeds from the dry petals.
You can also collect seed pods before they are fully ripe (as I’m doing in this video). This is helpful if you have a short growing season or didn’t stop picking flowers in time. Simply place the green seed pods into a jar with water in a warm, bright place to finish maturing. I’m using our greenhouse. Make sure not to overstuff the jar with stems and allow some space between the pods, as they can rot if they’re touching too closely.
Store the seeds in a dry, dark, and cool place, such as a breathable paper bag or envelope. Don’t forget to label the bag with the date and the variety of dahlia you collected.