Cut open the mature cantaloupe. Scoop out the seeds and pulp with a spoon.
Separate the seeds from the pulp. Rinse the remaining pulp from the seeds with cool water.
Spread the seeds out on a sheet of wax paper in a single layer. Allow them to dry thoroughly, which takes between one and three days.
Store the seeds in a sealed jar. Label the jar with the cantaloupe variety and year harvested. Keep the seeds in a cool, dark location and plant within four years.
Fill a 3-inch diameter plantable peat pot with a moistened soilless potting medium. Plant the seeds indoors three or four weeks prior to the last possible frost date in your area. Cantaloupes require three months to reach maturity, so starting indoors ensures a long-enough growing season.
Sow one cantaloupe seed per pot, planting the seed at a 1-inch depth. Cover the pot with a plastic bag to retain moisture during germination.
Place the pots in a warm location. Remove the bags when sprouts appear, usually within one week of sowing.
Transplant the seedlings outdoors after the danger of frost is past. Dig the planting hole 1/2 inch deeper than the peat pot and twice as wide. Set the pot in the hole so that the rim sits just beneath the soil surface, and fill in around the pot with soil. The pot breaks down after planting. Space plants 18 inches apart in rows 5 feet apart.