Growing gourds for birdhouses is an easy and fun project for the whole family. Gourds, although they grow on rather large vines, are really easy to grow if you have the space for them. Basically, if you just plant a few seeds in a 1" deep hole and keep them watered, they will take off. One plant can produce 10 to 20 large gourds. They will typically be about 8" to 15" tall, depending on the variety, and are just the right size to make into a birdhouse.
Gourds can be harvested in the fall after a good freeze which will kill the plant. Cut the gourds leaving as much stem at the top as possible. Place them in a dry location to finish drying and curing the gourd. This can be outdoors or indoors as long as they can be kept dry with good air circulation around them. It will take several months for them to cure. You can check them by shaking the gourd. If dry seeds rattle inside the gourd, they are generally ready to work with.
The nasty (by now) outer skin layer will need to be removed. If you want to leave the gourd natural, you can just sand off the loose material and leave it as is. In order to paint or decorate the gourd, you will need to scrape off most of the skin.
The best way to accomplish this is to soak the gourd in hot tap water for about an hour or more. A nice sized tub works well for this and I find it's easiest to do several at one time. Place the gourds in enough water to cover them. They will float so will need to be anchored under the water by either placing a board with a heavy object like a rock on top of them or another tub weighted down and placed over them will keep them under the water.
Now comes the fun (and messy) part. A kitchen table knife or other scraping tool works well to scrape as much of the skin off of the outside of the shell as you can. If it dries while you are working with it, dip it back in the water and keep scraping. Once you've scraped off as much as you can with the knife, let it dry and use a metal kitchen scrubby or even sandpaper to get the last little bits of skin off of it. A little extra work at this point will make a much smoother gourd and will be much more enjoyable to paint and decorate.
The next step will be to drill a 1" hole in the side of the gourd. Holes can be anywhere from 7/8" to 1 1/2" in diameter depending on the type of bird you want to attract to your nest. Once the hole is drilled, a gourd tool or a plain fork will work well to reach through the hole and pull out all of the seeds and dried material. It doesn't have to be thorough since leaving some in there will provide nesting material for the birds. After cleaning out the gourd, drill a few small holes in the bottom to allow for drainage.
Your gourd is now ready to use "as is" or ready to be decorated in any way that you want. Gourds can be painted using any type of paint that you like. My experience has been with acrylic craft paints to tole paint a design on the gourd, or even outdoor type spray paint. It's a good idea to put several coats of polyurethane over the paint to protect it from the elements.