Dahlias are a great flower for pollination experiments. There are so many varieties in colors, shapes of blossoms, size of plant that you can get almost an infinite number of possible outcomes. Records exist dating back to the 19th century, of botanists working on various dahlia combinations. The seeds of some of these experiments were very expensive and highly sought after. The home gardener can carry on this same project with almost no expense. Following a few simple guidelines will ensure that the seeds do develop successfully.
Purchase a few dahlias with different characteristics that you like, if you don't have them growing already. Since you want the offspring to be a quality seed, make sure you find the healthiest plants. If your nursery has limited dahlias, look around for other garden stores in neighboring towns for more genetic variation.
Choose a healthy flower with the characteristics that you like to be the male flower. Cut it from the plant and make sure it has at least a few inches of stem. Pull out all the petals and place it in a cup of water and bring inside to make sure it doesn't lose its pollen to foraging bees. Let it sit there for about a week while the female flower is readied.
Find a healthy flower to be your female receptor for the pollen. Dahlia flowers have both sex organs on the blooms but the pollen is released first and when it is gone, the female stigmas are ready to receive their pollen. This prevents self fertilization. Pull off all the petals and cover the flower head with the gauze and rubber band. This will prevent it from being fertilized by passing bees while you wait two or three days for it to ripen.
Remove the gauze hood from the female flower when you see that several of the stigmas are open. Take the male flower you selected earlier and rub it against the top of the female flower. This will make sure that the pollen has good contact with the stigmas and therefore a good chance of producing seeds.
Keep the seed head covered with the gauze hood until you see that it is turning brown and shriveling, usually about four or five weeks. Cut it off the plant and bring it inside. If it has not turned light brown, let it dry more. Once the head is dry you can open it up and remove the seeds.
Make a label from the chart listed in the Resources section. Keep this label on the envelope where you store the seeds and make sure you keep track of the different parents and their characteristics.
Grow these seeds you have manipulated and see what kind of new variation you have created. This can become a fascinating hobby and who knows, maybe something you develop will become highly desirable.