Gourds have similar growing requirements to winter squash. Unless trellised, they require large amounts of space, full sun and a long growing season to produce the largest specimens. The fruits are not typically grown for their food value but instead used for ornamental purposes.
Leave the fruits on the vines as long as possible allowing them to reach full maturity in the garden. Harvest after the skins toughen and prior to the arrival of freezing weather. Bring the harvest into a protected area like a garage or barn and allow them to cure. We spread them evenly on screens so that they are not touching each other and air can flow around as much surface area as possible.
In several months they will dry to a hard, wood-like exterior and the interior will have dried to a point where the they sound hollow with seeds rattling.
At this stage, the exteriors may have all kinds of colorful molds and fungi growing on them. Don't worry. Wash in a mild bleach solution, scrub with a stiff brush, and allow them to dry again. They now should be ready for sanding, carving, shaping, painting, or whatever else you are planning to do to them.
Check out the beautiful gourd art of Bonnie Gibson. Her site illustrates what a master artisan can do with a simple gourd. www.arizonagourds.com
The American Gourd Society promotes interest in all activities relating to gourds: cultivation, historical uses, gourd show competition, craftwork, and artistic decoration.