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I get a lot of questions about looking after houseplants, especially in winter. People tend to be disappointed by my answers, though, because what they really want is is a quick easy solution and it doesn’t always work that way. Gardening is always context-dependent. In other words, what works for one plant won’t necessarily work for another. So tip #1: Know what you have and know what it likes. This applies to any form of gardening, really.

Anyway, I thought I’d set down some ramblings. It isn’t going to be a simple “here’s how”; instead I’m going to do a whole series of posts about what plants need, especially in the context of keeping them indoors, from a scientific point of view (I majored in biology). It won’t always be light reading. What you get out of it, if you stick it out, will be up to you. I’ll break it up into a series of posts so any one post doesn’t get too burdensome, but each post in a given topic will follow upon the previous one.

I’ll start with light.

First, a short physics lesson.

Electromagnetic radiation, to put it very simply, is a type of energy carried in waves. What we think of as light is a very narrow band of that radiation that we happen to have the physiology to detect and interpret. This selection of EM radiation is called the visible spectrum. Each wavelength of the visible spectrum corresponds to a different colour, and the colours can roughly be set into seven groups: the seven colours of the rainbow.

When light strikes an object, some of those wavelengths are absorbed, and some are reflected. The wavelengths that are reflected are the ones that make it to our eyes, and that is the colour we perceive the object to be. If an object reflects red wavelengths and absorbs the rest, our retinas detect those reflected wavelengths and send certain signals to the brain, which then interprets those signals as “red” (or 紅色 or carnë or rouge or rojo or whatever you want to call it). Something that reflects all colours is white, something that absorbs all colours is black, and something that transmits colours (allows them to pass through it) is transparent.

The same applies to chlorophyll. Plants (most of them) appear green because chlorophyll reflects green wavelengths and absorbs the others, harnessing the energy they carry to fuel photosynthesis. So it’s a little ironic that green, so romantically considered to be the colour of life and fertility, is in fact the wavelength that generally contributes the least to said life and fertility.

Of course, not all plants are green. Those plants make use of other pigments to conduct photosynthesis, pigments that do absorb and use green wavelengths. Many green plants, especially deciduous trees and shrubs in temperate climates, use those pigments as well as chlorophyll, simply as a way to use a little bit more of the light they receive (actually, some of them have other functions, or are waste products). However, chlorophyll seems to be the most efficient at photosynthesis, so the plants rely mostly on that and the higher concentration of chlorophyll masks the other pigments. In autumn, the chlorophyll is recalled into the plant’s body but the other pigments are left behind, and this is why leaves change colour.

I’ll get to houseplants in the next post.

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