Janet, here is the plant I asked you about, that keeps growing a leaf on top and losing a leaf from the bottom.It's beautiful, isn't it? But I want it to stay that way. Also, the bottom of the trunk is so tiny, the top so big. - A.H. -
This is a dieffenbachia. It's probably Dieffenbachia amoena, if you need to look it up. D. amoena is bigger overall and with a wider leaf than the other really common dieffenbachia, D. maculata (but the two are pretty much the same in all other regards, such as where they grow best.). People call it dumb cane because should you get the sap into your mouth and the immediate intense pain that causes didn't stop you from swallowing some, it can so affect your tongue and mucous membranes that your speech may become unintelligible for a while -- you'd be "dumb." The sap can also badly inflame the eye-- both the cornea and the white. So if you do any of the clipping I'll mention in a bit, keep your hands away from your face until you wash them!
(In The American Medical Association's Handbook of Poisonous and Injurious Plants, this plant and treatment of the problems it can cause, is covered. Cooling liquids, pain relievers, and time are prescribed. There is no systemic poisoning, just the problems with the points of contact.)
Okay, back to the dieffenbachia as just a very good houseplant, which it is because it grows so well in dim light. That yours is dropping lower leaves may be simply because it's getting older. This plant does this, seems to be the consensus among the experts. Sometimes a dieffenbachia may lose lower leaves because it's cold (below 60F on a regular basis) or because it's dry, but you'd probably not see such great growth on the top if either of these was the reason.
One person I talked to, who's taken care of more interior plants than any dozen other people (she maintained commercial interiorscapes for 20 years), says that you can probably keep your plant going a god while longer if you increase the light and the fertilizer. However, she says, most of the time when these plants got to the point of dropping the lower leaves her plan was to replace the plant with a new one, and cut up the original for new starts. She also liked to grow this plant as a 3-plant cluster, if the place where it grew had the room for it to spread out.
So for your plant, you can wait a bit until it starts looking bad, and then start over. Do that by cutting the top 2 leaves off, break off the lower one so there's an injured node at the bottom of the cutting, and then root that cutting in water or in a sand-peat mix. You can make more cuttings at the same time, so you can perhaps make that 3-stem cluster. Cut the stem below the tip into 3" sections and take off the leaves, lay the stem cutting horizontally, half buried (like a driftwood log that's laying on the beach with sand banked up around it) in a sand-peat mix, and let it root and sprout. If you keep cutting, making more new plants and all you leave in the pot is a leafless stub, it's likely to sprout, too.
Hope that helps, re the dieffenbachia.
Oh - re the tiny basal part of the stem. Still looking for verification of what I think is going on, that this is primarily an understory vining/leaning species that never really needs to thicken its trunk. So if growing conditions improve as it climbs, it bulks up there without compensating below. You'd probably have to keep it propped for years before it added any girth there...
Thanks for asking. It was fun to go looking for opinions and written reports of dieffenbachia leaf loss. Really. I kind of had to make myself quit... I think Steven and I had a dumb cane long ago but it seems like we got rid of it when we found out the cat might get into trouble if he chewed on it -- that cat was a first class plant molester.