The Ohio State University has an Extension fact sheet on "Growing and Curing Gourds in the Home Garden" which can be found at http://ohioline.osu.edu/hyg-fact/1000/1630.html. The information below is taken from the fact sheet.
The birdhouse gourd is in the Lagenaria family: “Gourds are ready for harvest when the stems dry and turn brown. It is best to harvest gourds before frost. Mature gourds that have a hardened shell will survive a light frost, but less developed gourds will be damaged. The Lagenaria will tolerate a light frost; but gourd color may be slightly affected. Gourds should be cut from the vine with a few inches of the stem attached. Take care not to bruise the gourds during harvest, as this increases the likelihood of decay during the curing process. Discard any fruit that is rotten, bruised or immature. After harvesting, gourds should be cleaned with soap and water, dried, and rubbing alcohol applied to the surface.
Curing Cucurbita gourds is a two-step process which may take one to six months depending on the type and size of the gourd. Surface drying is the first step in the curing process and takes approximately one week. During this time, the skin hardens and the exterior color of the gourd is set. Place clean, dry fruit in a dark, well-ventilated area. Arrange gourds in a single layer and make certain that the fruits do not touch each other. A slatted tray will allow air circulation around the gourds. Check gourds daily, and discard fruit that show signs of decay or mold and any that develop soft spots.
Internal drying is the second step in curing and takes a minimum of four weeks. Keep the gourds in shallow containers in a dark, warm, well-ventilated area. If any mold appears on the outside skin, gourds can be wiped clean and allowed to continue drying. However, any gourds that become decayed, shriveled, or misshapen should be discarded. Periodically turn the fruit to discourage shriveling and promote even curing. Providing warmth during the internal curing process will accelerate drying and discourage decay. Adequate curing is achieved when the gourd becomes light in weight and the seeds can be heard rattling inside. Cured gourds can be painted, waxed, or decorated.
Lagenaria gourds can be surface cured in the same manner as cucurbita gourds. However, the internal drying process takes much longer for the gourds to fully harden. After curing, the surface can be smoothed and polished with very fine steel wool or sandpaper. The hardened shell should be treated with rubbing alcohol, allowed to dry, and then waxed or shellacked for the final finish.”
After the gourd is fully dried (seeds rattle when the gourd is shaken) and the finish of your choice is applied, you can drill the holes for hanging, drainage and bird entrance. For hanging, just drill a couple of holes through the neck of the gourd and use copper wire, string trimmer cord, or such to hang the gourd. For drainage, drill 5 to 7 holes (5/16 inch) in the bottom of the gourd, about 2 inches apart. For the entrance hole, use a 2 1/8 inch hole saw to cut the entrance hole somewhere on the widest part of the gourd.
