If you live in warmer southern climates, saving Petunia seeds will not be much of an issue for you; however, if you live in a colder climate region, then your Petunias will usually die in the winter and you will need to save Petunia seeds and re-plant the following season.
Saving Petunia Seeds – Why Save
If your Petunias are annuals rather than perennials, you need to save your Petunia seeds each year in order to avoid buying new ones.
A Note about Hybrid Petunias
Before you get started saving your Petunia seeds, you should be aware that seeds from hybrid petunias should not be saved and used for a new planting if you are looking for the same type of Petunia that the seed came from. Hybrid seeds are created by inbreeding different parent plants and can only be re-created by breeding the exact two types of parents again. However, if you're adventurous and are willing to take a few chances, hybrid seeds can produce something unusual and very interesting.
How to Save Petunia Seeds
Petunia seeds are located in the plant’s seed pod. The seed pod is also referred to as the calyx, and is usually located at the base of the flower. You should wait until a flower dies on its own before trying to remove the seed pod from the flower. Generally speaking, it's not a good idea to deadhead Petunia plants in order to get seeds.
Once you find a good dead flower for seeds, you'll find the calyx located inside the sepal of the flower. You'll recognize the calyx as a bulging part of the stem that is located directly beneath the base of the Petunia flower. After the Petunia flower dies, it will fall to the ground, and the calyx will begin to swell and turn brown. After a period of a couple of days or so, the calyx will split open and the seeds will fall out.
You can pick the calyx off the plant before it opens or tie a piece of pantyhose or other some other very light type of material to catch the calyx so that it does not hit the ground and spill its seeds. If you pick this calyx before it opens, place the paper bag placed the calyx in a paper bag for storage until it splits open.
After you have collected the seeds from the calyx, you should allow them to dry for about a week or so. You'll be able to tell that the seed is dry if you can't bite into it or smash it. Once the seeds are dry, store your Petunia seeds in an airtight container such as a small food jar or small Tupperware container. In order to keep the seeds dry, you can also add small packets of silica gel to absorb any moisture that might get into the container.
Once you have placed your seeds in an appropriate, airtight container, keep the seeds stored in a cool, dry place. Temperatures of around 32° to 42°F are usually best for Petunia seeds. Also, make sure to label the container so that you know what type of seeds they are.