St. Paul, Minnesota is a great site to grow melons with its rich soil and weather melons can grow very well. You can save the seeds from heirloom melons to use for seed next year.
You must wait until the melon is completely ripe before you use it for next years seeds. If the melon is not ripe the seeds with not grow.
Once your melon is ripe cut it open and dig out the seeds with a spoon. Then seperate the seeds from any soft melon and place them on a paper towel to dry.
When the seeds are good and dry you can place them in a envelope that is labeled with the type of seed in it. You should also put the year on the envelope so you know when the seeds will be good for planting.
Most seeds are only good for a year after they have been saved so it is a good idea to use seeds that have only been from the previous year.
Store your seeds in a cool dry place that will not freeze. If you store them in a humid area they will mold, rot or even sprout and then they will not be good to use for growing new plants. Most seeds will not grow if they have been allowed to freeze.
Saving your own seeds can save you money and if you harvest the seeds from organic plants then the seeds willl be organic.