Yikes, that's a cold place to even imagine a lemon tree growing! Sending warm thoughts to you from Florida . . . for what it's worth.
Um, Rob I don't mean to complicate things but I'd deep six those marble chips outa there. They are quite alkaline and will leach calcium into your soil which your lemon tree doesn't need.
Also putting rocks or other coarse material in the bottom of a pot is an old idea that's been found to not work well. In fact it can do the opposite of aiding drainage by causing what's known as a "perched" water table in the pot where the water stays in the soil above the rock layer. Just use the same soil all the way to the bottom for best drainage.
