I went over to take a look. I pulled up the carpet in the interior corner where the owner told me the tree had been (she had already clipped it). Right there, on top of the padding, just below the carpet, was coil of white vine. The air smelled like potato.
"I think it's a potato."
"We just planted potatoes outside along that wall!"
This house is more than 100 years old. The first time I went down to this basement I noticed the floor's hills and valleys. It's wood set in sand. Over time the earth's moisture rots the wood making the perfect compost to grow potatoes and trees, not to mention providing the perfect home for bugs.
I've renovated two houses of this same vintage, and both had basement floors like this, built right on top of earth. My solution isn't for everyone: I dug two feet down, poured in six inches of gravel, then laid down rebar, a maze of radiant heat pipes, and then four inches of concrete. It's something that needs to be done when you first move in, unless you can take a major disruption.
It's all a question of what you can live with. If your basement smells bad and you can't take it, or your foot goes through the floor, or things are getting ruined because of dampness, you might want to consider digging down, laying down rigid foam insulation, and pouring a concrete slab. Then, flooring. If done right, a floor like this will last 200 years.
This particular client is not interested in a major disruption. They've lived with the wavy floor and occasional dampness. Knowing that, I broke off the vine and pressed the carpet back down on its tack strips.
I'll visit in a few months and look for more vines and the makings for home fries.
