let me try to clarify this a little. California has Agriculture Inspection Stations at most border crossings. all vehicles must go through the station. sometimes they just wave you through, sometimes they stop you and ask questions like, do you have any fruits or vegetables? where have you been traveling? do you have any firewood? if you surrender what ever they want that's the end of it. if you try to lie to them that's a different story, they will tear your vehicle apart if they want. you can't bring any produce, live plants, firewood, etc, without the correct paperwork. now after scarring the pants off everybody. I have crossed the border thousands of times and never been searched, I have some funny stories but nothing bad. and yes I have taken produce across the border and not declared it.
so about the house plant when you pull into the station if they can see it they will take it, no use trying to lie if they can see it. highdesertranger