Watering spike for 2L bottle

I'm leaving for my honeymoon in a couple of weeks, so I needed a way to keep my plants alive between the times when the neighbor will stop in to water everything. So I made this watering spike.

My bit of testing showed that it took about 12 hours on average for the water in the 2L bottle to drain. It lasts a little longer if the ground is wet to begin with.

EDIT 7/26/11: Spike with Threads added. This one also includes 3 "fill layers" in the middle of the spike, which makes a sort of filt