Guide to Caring for an Unknown Plant 2: Leaf Color and Light

You’re on your way back from the plant store, an unplanned but pleasant detour after a day’s shopping. On a whim, you buy a plant you’ve never seen before, but which you really like. To make matters worse, the store doesn’t identify it. So how do you know how to care for it?

This article is the sequel to Guide to Caring for an Unknown Plant 1: Plant Type and Light.

Foreword

This second guide is also about light. Having seen in the previous guide the link between plant type and lighting requirements, we now turn our attention to leaf color. The third guide will deal with watering, and the fourth with other aspects of plant care (repotting, potting soil, fertilization, temperatures, propagation, etc.).

To illustrate the article’s objectives, we’ll take a look at this mystery plant and, based on the information given in the article, draw some conclusions that may help us understand its need for light.

N’hésitez pas à aller relire les principes de base sur la lumière dans l’article précédent.

Answers to the Practical Exercise (Guide 1)

At the end of the first guide, these three photos were presented and you were asked what the observation of the plants suggested about their light requirements.

1) You can see from the photo that the plant produces a trunk, which is quite straight, by the way; it’s probably a tree in the wild. It should be given at least indirect bright light, with some direct sunlight, depending on observation of the plant only.

Plant name: Schefflera.

2) The healthy-looking plant begins to fall over on its side. Fleshy roots can be seen at the corners of the nodes (adventitious roots). This is a climbing plant: it would like a lot of light, but will accept medium light.

Plant name: Syngonium podophyllum (and indeed, it tolerates even low light).

3) This plant is neither a cactus, nor a tree, nor a climber. It may look like a rosette plant, but it’s getting a little too big to be considered as such. However, three important details stand out: the absence of leaves, reminiscent of a cactus; the fleshy stems, which are reserves against desert conditions; and the bluish tint caused by the bloom the plant produces to protect itself from the sun. So it’s well-suited to growing in the sun!

Plant name: Aloe vera

Those familiar with its cultivation might be inclined to mention that aloes tolerate low light; however, it’s rather that aloe is the exception. It tolerates many years in low light, but pays the price by wilting and developing limp leaves. As a general rule, plants like aloes need lots of light (and grow much better in it!).

Another Important Feature: The Color of the Leaves

Leaf color, a particularly obvious characteristic, tells us a great deal about a plant’s need for light. This is particularly interesting when looking at different cultivars of the same plant: once we’ve identified the basic plant, or type of plant, we can refine our understanding of its light requirements.

The principles of photosynthesis are undoubtedly highly complex, but for the purposes of this article, we’ll simplify: it’s green that enables photosynthesis, nothing more, nothing less. We’ll divide plant leaves into three categories:

1. Leaves that are entirely green photosynthesize optimally. These plants, especially dark-green ones, are therefore naturally more tolerant of lack of light.
2. Next, medium-green leaves: this subgroup includes plants whose leaves are derivatives of green. For example, chartreuse (neon) plants are a mixture of green and yellow. They can therefore photosynthesize properly, but not as well as if the leaves were entirely green. We also see silvery leaves (green and silver), greenish-pink leaves and dark leaves (mauve or vaguely burgundy); in short, the more green there is (somewhere, even mixed), the better the leaves can photosynthesize.
3. Finally, the subgroup of leaves with hues that can’t photosynthesize. Generally speaking, these leaves are not entirely colored – when they are, as in the case of entirely albino (i.e. white) plants, the plant lives on its reserves and eventually dies, since it cannot photosynthesize. This category includes bicolored plants with white, pink or other variegation. The more imposing the variegation, the less green the plant and therefore the less able it is to photosynthesize: it therefore needs more light intensity.

It is of course by combining observations on plant type and leaf color that we arrive at a precise answer.

Applied Example: The Mystery Plant

Based on the information we have about the type of plant, what can we say about its light requirements?

Two hues can be seen on the leaves of the mystery plant: dark green and pale green. Both shades can photosynthesize, suggesting an increased tolerance to lack of light.

Since we’ve already noticed its rosette-like growth, a sign that it’s a lowland plant, we might be inclined to give it medium light. On the other hand, to produce flowers, it needs bright light.

So here’s my verdict: the mystery plant tolerates average light, but only flowers in bright light.

Practical exercise

In the next article, we’ll talk about plants’ water requirements. In the meantime, what can you tell about the following plants by observing their characteristics? Feel free to write your answers in the comments. Answers will appear in the next article.