Measure the diameter of the bird-feeder pole using a tape measure. Most poles measure a half inch or 5/8 inch in diameter. Purchase a piece of metal rod the same diameter as the bird-feeder pole from a home improvement or hardware store. Purchase a metal coupling made for the size of the rod.
Cut the new piece of metal rod to the desired length using a hacksaw. Cut the rod square so that it fits nicely into the coupling. Use a fine-grit sandpaper to remove any burrs from the end of the rod and to make it smooth.
Fit one end of the coupling over the end of the bird-feeder pole and insert the extension rod into the other end of the coupling.
Heat the coupling connections with a propane torch and apply silver solder to the heated connections. Move the end of the silver solder around the entire circumference of each connection to ensure a bead of solder applies all the way around. The solder will hold the rods together more securely. Place the bird feeder into the ground in the desired location.