Alternatives to extension cord over the grass to light a Christmas tree
This is what we sell quite a bit of, more at this time of year than other times.

Some people call them rocket post, or landscape post.



This is the post...



This gives you an idea of what you can add to it...



Click here to get the color flyer

Basically if you have a receptacle outside in a convenient location you can remove the weather proof cover and put this on...



...run conduit from one of the 1/2 or 3/4 threaded hubs (your choice when you buy) and run PVC to the post.  At the post end you just end the PVC run with an elbow to come through the ground.  You keep the top of the post blanked off or put almost any landscape light you want on top of it.  It has a 1 gang opening one 2 sides and you can put in a low voltage divider.  That way if you put the post in a place that you want a TV, Telephone, computer, speakers...you can use the post with a separate PVC.

Remember you will have a local code to follow and turn off all power when working on it.  Our local code says Schedule 80 PVC or ridged galvanized conduit wrapped in 50 mil tape that breaks the ground, 18 inches deep, GFCI circuit and these are just what I'm highlighting.  Depending on code you can use UF underground feeder (like 12/2 W/GRD UF)

Good Luck!