One of the things that excited me most about moving into this place was the possibility of having two large planters. As soon as I saw them I started planning how I was going to arrange my cactus and succulent collection, which I did. It was a great spot, because they got plenty of light and were protected from my cats. Everything was perfect, until I discovered that my Echeverias no longer looked like giant rosettes, but ugly and lanky.
This irreversible phenomenon that destroyed the aesthetics of my plant is known as etiolation and has to do with the amount and direction of the light it was receiving. It was at that precise moment that I began to learn a little more about the light requirements of plants, as it is necessary to understand these processes in order to offer them the best conditions for their growth. Today I am going to share with you what I have learned on the subject, including the classification and groups of plants according to their need for light.
Importance of natural light for plants
Light is essential for the development and growth of plants. Almost everyone knows that it is essential for photosynthesis, that process by which the plant processes its own food, allowing it to store glucose and provide energy for all its cells; but few people recognise that there are 3 other processes that depend on light: phototropism, photoperiodism and photomophoresis.
Phototropism, which responds mainly to blue light, causes the plant to grow or move in the direction of the light, although there are cases of negative phototropism, in which the opposite occurs. Plant shoots grow towards the source of light energy. This movement occurs because in plants there is a protein called phototropin, which are light receptors that absorb the blue part of the spectrum. When activated, they are able to affect the behaviour of other plant proteins and hormones such as auxin, which promotes cell elongation.
Auxin concentrates in areas where there is no incidence of light, causing those cells to grow, tilting the plant towards the light source. This mechanism is responsible for etiolation (what happened to my poor echeverias), which stretches the plants to receive more sunlight.
Negative phototropism is an interesting mechanism of some plants like Monstera Deliciosa. When this plant does not get enough light, instead of moving upwards towards the sun, it will tend to move towards the shade. It is not that it wants to commit suicide, it is just that in its natural habitat the monstera grows in the shelter of large trees, so the plant will instinctively seek the thickest shade because it will come from a tall tree, which it will climb to better reach the sun's rays.
Photoperiodicity expresses the plant's response to the amount of light and darkness in a 24-hour period. Believe it or not, plants are able to measure the length of day and night quite precisely. These sun/dark exposure intervals will determine flowering, germination and other processes.
This circadian rhythm is made possible by a pigment called phytochrome, which are protein pigments located in the leaves that are able to detect these seasonal changes. The length of the daylight hours serves as a signal to stimulate particular processes such as flowering or metabolic activities among others, including stem growth, leaf fall and root development. This pigment reacts mainly with red and far-red light of the light spectrum.
Photomorphogenesis is plant growth controlled by light, but not related to photosynthesis. They are responses to high intensity blue light and are directly dependent on the amount of light received, both in wavelength and total amount, as well as on the activity of phytochromes.
Natural vs. artificial light
Not all light is the same, they vary in intensity and quality so that one type of light may stimulate certain processes but prevent others, so it is essential to understand the importance of the type of light provided to the plant. Undoubtedly, natural light is the best of all and plants, regardless of their classification, should have adequate access to it.
To give you an idea of the big difference between natural and artificial light, the light inside your house produced by a light bulb is no more than 500 lux, whereas natural light on a sunny day outside can reach 100,000 lux. On the other hand, natural light offers a much more varied spectrum than artificial light. Let us remember that sunlight has the whole spectrum of light, with all the colours of the rainbow, but especially red (which is responsible for the elongation and flowering of the plant) and blue (which determines growth and germination).
Please note that when I talk about artificial light, I am referring to the ordinary lighting that we use in the various rooms at home or in the office, with an ordinary household light bulb. Special lamps for indoor plants can provide everything that plants need to grow and are a simple way of ensuring that your plant collection gets everything it needs, regardless of the natural conditions of the space in which they live.
Classifying plants according to light requirements
Sorting plants according to light requirements is a simple way to understand the needs of your plants and to know if they will be happy where you plan to place them. So simple that if you know that you have a lot of direct light on your balcony, then you will look for full sun plants that can make the most of those conidtions. do you live in a flat that looks like a cave? Then you get plants whose light needs are more flexible. On the other hand, knowing about the photoperiod will allow you to understand certain processes of your plants.
According to their photoperiod
The photoperiod is the number of hours of uninterrupted light the plant will receive in a 24-hour period. This refers not only to direct sunlight, but also to the length of the period of light (day) and darkness (night). This time range varies with the seasons, becoming longer in summer and shorter in winter. As plants cannot consult the calendar or ask for the date, they use these environmental clues to know what season it is and to see if it is propitious to start certain processes such as flowering.
The photoperiod is fundamental to the plant's metabolism. If photosynthesis is responsible for creating its food, it is the photoperiod that regulates the growth and direction of leaves, flowering, germination and more. A plant drops its leaves in autumn, survives the winter and is reborn in spring thanks to this process. It is also possible to use it to force certain species to flower. have you ever wondered how it is that some plants like Kalanchoe Blossfeldiana are always in bloom and looking beautiful in nurseries? This is because they manipulate the photoperiods, placing dark bags over the plants to simulate shorter days and make them think it is time to flower. It is also done to produce certain foods out of season.
From a photoperiod perspective we could classify plants into three main groups:
Short-day plants are those that produce flowers when indicated by phytochromes that sense red light (from sunset) and far-red light (which is even less intense). When they receive more of this light, they start flowering. This means that short-day plants grow and develop more when they are exposed to less light, as they are able to speed up their metabolism and processes. These plants require light periods of no more than 14 to 12 hours maximum.
Most of them come from tropical, subtropical or low latitude areas. This particular cycle is said to occur because these species originated in tropical locations, where winter (and thus shorter days) coincide with the rainiest time of the year and their harvests are before the dry season.
Some short-day plants, which usually flower in autumn or spring, are poinsettias, Christmas cactus, mystic rose, cyclamen, chrysanthemum, primrose. Short-day cereals and vegetables include sweet potatoes, bananas, as well as rice, sorghum, sugar cane, tobacco and maize.
In long-day plants, the opposite occurs to short-day plants, as intense red light inhibits flowering: The plant interprets these light changes as the onset of autumn and winter days, so it begins to prepare to go into hibernation. These plants require prolonged exposure to light, preferably more than 14 hours a day.
Such plants are able to perceive low temperatures as an indication that they should remain in a period of dormancy, a death of vegetative state that allows them to tolerate the cold better than the reproductive state (flowering to seed). Accumulating a certain number of hours sleeping underground will guarantee that they will grow and flower when the winter is over. This is why you cannot have plants originating from places with distinct seasons in tropical locations.
Long-day plants usually come from mid and high latitudes. They are associated with summer and it is believed that it is the short periods of darkness that actually trigger the flowering cycle. Examples of such plants are celosia, gaillardia, coreopsis, rudbeckia, poppies, clovers, wheat, peas, barley, onions, spinach, lettuce, beets, among others.
Just as there are some people who are very sensitive to certain stimuli and others who are completely indifferent, there are plants that do not like the hours of light or darkness. Whether the day is longer than the night or vice versa, day-neutral plants have their own rhythms, dictated by age or other stimuli, which determine their flowering times. Some of these species are petunias, dandelions and sunflowers. Watermelon, melon, hyacinths and daffodils also fall into this classification. In fact, it is believed that there are varieties of plants that managed to adapt to other photoperiods and became insensitive to these conditions. There are varieties of maize that can adapt to temperate zone cultivation, even though it is native to the Americas.
According to location
This classification refers to the way in which the plant should be illuminated. This depends on the environment in which the species originates. Thus, plants that come from tall, protected forests will require indirect light, while taller trees, vegetables and others will need to receive the sun's rays more intensely and directly. According to these criteria, plants will be classified into these 3 basic groups:
Full light plants
Full light plants are those that require the direct incidence of the sun's rays on their leaves in order to carry out their processes. All trees, including bonsai, are full light plants as can be seen from their dimensions. Likewise, scheflera, bamboo orchids, cacti, as well as all vegetables and flowers such as roses are plants that must receive a lot of direct sunlight, so you should place them outdoors or at least on a terrace or window.
Plants, all plants, require even a minimal amount of light in order to grow as it is essential for photosynthesis. That said, shade plants are those that come from places protected by thick tree canopies or that grow in the shelter of other species of trees or taller plants. They can remain indoors and will grow happily even if they are not so close to a window, in fact if they receive direct sunlight they can get burnt. Examples of these are Sansevierias, Peace Lily and Zamioculcas.
Semi-shade plants usually come from tropical rainforests, where they receive filtered light from the canopy of taller trees and plants. They require high levels of humidity and many are climbers. This can be a difficult concept to understand, especially as it is often confused with shade. Semi-shade or partial shade plants should be protected from direct sunlight, but in a well-lit location. If they are very close to a window, for example, you should at least filter the sun with a curtain. A well-lit, but north-facing space that receives hardly any light in the late afternoon would be perfect for this type of plant. Examples of semi-shade plants are calatheas, monsteras, ferns, dracaena, succulents, among other indoor tropicals.
Dedicated to creating an army of cacti, succulents, poodles and cats to help me conquer the world. In the little free time I have left, I play, write and dance.