Why doesn't the dirt in my flowerpots disappear?

Dear Matthew Alice:

Plants grow because you give the good soil and water them, right? So why doesn't the level of soil in the houseplants that I've had for years gradually subside? Aren't the minerals in the soil sucked up through the roots to create new branches and new leaves?

-- Green Thumb Danny, the Net

Just out of curiosity, Danny, d'ya ever hear your philodendron weeping in the dark, crying out for nutrients? A ficus sobbing to be put out of its misery? I guess not if you have been able to keep your plants "for years." So from time to time, you must manage to throw your little green friends some fertilizer. Much more important than soil. In fact, almost any plant can be grown without soil. Soil is just a place to stick the roots so it doesn't fall over. You could grow a plant in Styrofoam peanuts, as long as you made sure it is bathed periodically in water and fertilizer. Common garden dirt is just crushed and eroded mountains. Not many nutrients in a stone. Your plants aren't sucking up dissolved dirt through the roots. They're living on the food you supply in compost-enriched soil or in fertilizer. Yikes. No wonder the rain forest is dying. It's all the bad vibes from suffering houseplants.