Shade or sun?
If you are about to acquire a new plant, the first information you'll want to know is how much sun it can take and how much water it should receive. One would think that such information is easy to come by and, indeed, most plant listings provide guidance about these needs. The difficulty arises when the guidance is followed to the letter and your plant languishes or dies. If you've ever had this experience, or you hope never to have it, what I have to share here will be of benefit.
I became curious about this when I acquired some tropical plants and was assured that they grew in full sun in their native habitat. This habitat was a tropical rain forest, so lots of sun and lots of moisture was the ticket, right? Well, I found out quickly that "full sun" in a tropical rain forest is nothing like "full sun" in south Florida. In fact, full sun in a tropical rain forest is more like part shade because of the broken cloud cover and frequent downpours. Compare that to a south Florida winter or spring day, where "full sun" is brutal, non-ending sunshine from dawn to dusk, with no clouds or breaks for rain. Plants that do just fine in the "full sun" rain forest environment will be toast in south Florida full sun.
Moist or dry?
Once I learned that full sun in a rain forest means part shade in south Florida, I then thought about moisture. Rain forest means, well, rain, and lots of it, right? Actually, that is true, but that doesn't mean the plant loves to be sopping wet. How is this possible? The key is in knowing what kind of root environment the plant's habitat provides. A plant growing on rocks or in loose debris on the forest floor is going to have a lot of air around the root zone. This is true even when the plant is exposed to frequent rain showers. Contrast this with a plant grown in a soil medium that stays moist all the time, even when no rain is constantly wetting it. Plants that need the extra root aeration are going to languish or rot when grown in soil that is always moist or wet. In lieu of the extremely open or exposed condition of the roots in their native habitat, such plants will require a drier soil medium. This seems counter-intuitive until you understand that sometimes "wet" is really drier than you think! Understanding this also explains how certain kinds of cactus thrive in a rain forest. That fact alone should be enough to get you asking more questions!
Whenever I have difficulty growing a particular plant, I wish for the kind of detailed information that is generally lacking. I want to know the seasonal conditions of sunlight and temperature, of soil and moisture, and of the community of plants that surround my garden specimen in native habitat. Instead, what I get is probably what the day was like when the discoverer of the plant found it. The day was sunny and the plant was growing out in the open, away from trees, so that means it likes full sun, and so forth. No matter that the day in question was the first time in two months that the sun had been out for more than an hour straight! See what I mean? But all is not lost, because often your plant will provide you clues about what it needs.
Coming up: If Plants Could Talk: Reading the needs of your plants
Photo credit: NWS public domain image