Some of us seem to be born with a green thumb, while others among us are constantly accused of houseplant homicide. Fortunately, for those of us who are herbology-challenged, there is a wide variety of cacti capable of tolerating our foibles. Cactus plants require little attention, can withstand infrequent watering, and do okay in a fairly wide range of temperatures. They may be the perfect option.
How does a cactus live without water? Well, simply put, it doesn’t—but it’s easy to understand why you might think otherwise. The truth is that cacti, like all living things, need water to survive. But they’ve evolved and adapted in ways that make them very efficient users of the water they receive. That means that they’re able to go long stretches between watering and get by well on just a little bit.
Whether you live in an area with a climate that is perfect for outdoor cactus cultivation or you’re just looking for a houseplant that you can’t kill—you can’t go wrong with a cactus. Once you understand all of the ways they’ve adapted to become resistant to drought, you’ll have a better idea of how to keep them happy. They will add beauty to your indoor or outdoor spaces and require little in return.
A Cactus Can Be Happy Without Much Water
Perhaps the first and most important thing that you need to know about cacti is that there are more than 1,000 individual species. In fact, the plant genus that is home to all cactus plants is so diverse that it includes some cacti that have leaves instead of spines. The natural habitat of cacti ranges from the southernmost tip of South America all the way north to western Canada.
If you’re like a lot of people, the first thing that comes to mind when you think of a cactus is cartoon coyotes or cowboys in ponchos with stubby cigars. But the tall, lobe-branched cacti that you see in those settings are just one of a wide variety of species. Unless you live in the desert southwest of the United States or in northern Mexico, that probably isn’t the best cactus to set your sights on.
One thing that works in your favor is that no matter what species of cactus you decide to bring home as an indoor or outdoor botanical confidence builder, you’ll be getting a drought-resistant and hearty houseguest. Let’s look at some of the ways that cacti have evolved to be such efficient water users.
The easiest way to recognize a plant as a member of the cactus is family is to notice what they don’t have—leaves! But that’s not 100% accurate for a couple of different reasons. The first reason is that their spines are highly-adapted leaves. The second is that some members of the cactus family have leaves instead of spines.
So why did most cacti evolve spines where their leaves ought to be? And how do spines make a cactus more efficient at water consumption than other plant species? The leaves of most broad-leafed plant species have at least two important jobs to do. First, they are an important part of the plant’s respiratory system. Second, they play a crucial role in photosynthesis. Many broad-leafed plants rely on their leaves to contribute significantly to their water gathering efforts as well.
The part of a plant that takes in the carbon dioxide that the plant will convert to oxygen during photosynthesis is called a stoma, and it is usually located in the leaf stem of broad-leafed plants. Of course, photosynthesis is the process by which plants convert sunlight to nourishment.
So, beyond taking in the fuel for photosynthesis, leaves also collect the sunlight that provides the missing ingredients. Cacti have come up with creative twists on each of these processes to become better at surviving without much water.
Most plants don’t have to worry about conserving water the way that cacti do. So, their stomata are located in places that tend to permit a great deal of evaporation. They open during daylight hours, which further compounds the rate of evaporation. Cacti can’t afford to be so cavalier with their precious stores of water.
Because most cacti have evolved and adapted to make survival possible in environments that would kill most broad-leafed plants, they’ve had to get creative about the respiratory and light-absorbing processes that they use to accomplish photosynthesis.
A cacti’s stomata are still located at the base of their spines, which we noted earlier, are just highly-adapted leaves. The spines themselves make a big difference in the rate of evaporation because of their reduced surface area in comparison to broad leaves. But the real difference in how a cactus plant’s stomata help them survive on limited water can be found in their adopted schedule.
Most plants take the easiest route between where they are and where they want to be. When it comes to photosynthesis, that means opening their stoma during daylight hours to take advantage of the abundant light. But if a cactus were to do this, they would lose unacceptable amounts of moisture to evaporation during the heat of the day.
Day and Night
Because cacti have to do everything they can to conserve water, they’ve adapted a unique biological clock that strikes a balance between the need to breathe and the fear of losing all of their stored water. A cacti’s stomata open at night when there is less risk of evaporation. Since desert environments have plentiful sunlight, they are able to get by on what they collect through the membranous coatings on their stalks.
Conducting all of their breathing at night means that cacti have to store the carbon dioxide that they take in overnight until they can use it in photosynthesis when the sun comes up. This is another evolutionary adaptation that makes cacti capable of doing what they do in the places where they do it.
We’ve already noted the difference that surface area makes in the different rates of evaporation between leaves and spines. The fact that a cactus taps the cells of its main body for light absorption means that cacti don’t miss the metabolic contributions that are lost in this trade-off. When you get right down to it, most cacti are nothing more than fleshy, leafless stems with an array of spines.
But why does a cactus have spines if the stomata are located on the stalk, and the stalk does the lion’s share of the photosynthetic work? There are two main functions that the spines serve in the life of the cactus plant. The first one is pretty obvious if you think about it, but the second function might not be as easy to pick up on just by looking at a cactus.
The first thing that spines do for a cactus is to protect it from grazing animals. Think about all of the broad-leafed plants that get munched on by birds, insects, and mammals. Now, think about how attractive a plant would be to those same grazers if it was located in the middle of a desert and filled with life-sustaining moisture. If it weren’t for their body armor of effective spines, cacti wouldn’t stand a chance.
Spines also do their part to help a cactus plant capture every drop of water that comes within its range. The spines may be angled to channel water toward the plant’s stalk and downward toward the root system, or they may be fine enough to gather the morning dew until it forms droplets that will fall to the ground. Each species has its way of doing things, but in the end, it’s all about the H2O.
When you look at a tree, you see a trunk, branches, stems, and leaves. When you look at ornamental or edible flowering plants, you see a stalk, stems, leaves, and flowers. But, as we noted earlier, a cactus is just a root network underground with a single stem that is covered in spines. The body of the cactus plant has a number of advantages that cacti rely on to survive in dry climates.
It isn’t as simple as changing one or two things about the way you do business when you set out to evolve and adapt to the harshest climates on the face of the planet. It takes an all-hands-on-deck approach. So, cacti have had to incorporate contributions from every part of its body to maximize water efficiency and become capable of thriving where other plants wouldn’t survive at all.
The stem or stalk that makes up the main body of a cactus plant is a highly specialized version of a trunk or stalk that you would find on broad-leafed plants like trees and flowers. It has evolved to be as efficient at water storage and conservation as it is possible for a plant to be. This has required cacti to adapt the internal composition, exterior surface, and even shapes that their main bodies feature.
Most cacti bodies are globular, and some even incorporate ridges. These features enhance a cactus plant’s ability to conserve water. Storage capacity and water retention are the primary concerns for most cactus plants, so it just makes sense that they devote so much of their bodies to ensuring that these two tasks get taken care of.
Of course, everything that lives also wants to grow and reproduce. Even the way that cacti approach these basic biological imperatives reflects the central importance of making the most out of the limited amount of water they get. The life cycle of a cactus plant is directly linked to its ability to gather, store, and conserve water.
Storage and Conservation
There are at least three key features of a cactus plant’s body that play important roles in the ability to store and conserve water. The first is the globe-shaped body style that many cactus plants have. The second is the presence of ribs or ridges on the body that act like accordion folds that allow the cactus plant’s body to expand as it absorbs more water. The third feature is a thick, waxy exterior surface.
The benefit of a globular body is that it offers more internal storage capacity with less exposure to the pressures of evaporation. Whereas a vining body-style like you find with ivy or a tall, thin stalk and broad flower like you find with sunflowers leave the plant at a disadvantage to evaporation, a cactus holds all of its water inside.
The ridges and ribs that accentuate many cactus plants’ bodies offer important benefits to this approach toward water conservation. When rain is infrequent, and dewfall is minimal, a cactus has to be able to grab as much as it can during the rare times when water is plentiful. If the plant’s body weren’t capable of accommodating the swelling that comes along with taking on water, it wouldn’t be able to make the feasts sustain it through the famines.
Of course, it wouldn’t matter how much water a cactus could absorb if it weren’t able to hold onto that water for long periods of time. The wax-like coating that is on a cactus plant’s exterior surface works like a waterproof raincoat in reverse. Instead of keeping the water out, it works to hold the water in.
Without getting too philosophical about it, we can probably agree that there is more to life than simply surviving. So, it makes sense that a cactus wants to survive not just for the sake of surviving but for the purpose of growing and reproducing. But with water at a premium, the cactus has to factor the energy demands of growth and reproduction into its plans.
That means that most cacti only grow larger during times when water is abundant. It also means that most cacti have evolved to go dormant with regard to blossoming except for those times when water is plentiful. In this way, their life cycle resembles those of other species that have evolved as highly-specialized desert dwellers. A desert landscape after a rainstorm will look vibrant for a time only to return to normal as things dry out.
But even the end of its life isn’t enough to get a cactus plant to give up its water reserve. Scientists have cut into the bodies of cactus plants many months after they have died only to find that they still retain the essential, life-sustaining moisture that they were storing when they died.
The final aspect of a cactus plant’s physical adaptations that need to be considered in relation to its water consumption is the root system. Most plants can rely on their root system for stability and water collection at the same time without having to make any trade-offs in the process. But for a cactus, that just isn’t the case.
Most cactus plants have shallow and broadly dispersed root systems. This means that all of the water gathering capacity of the plant is close to the surface. The approach makes sense when you consider the low availability of moisture deeper in the soils of desert landscapes. But the trade-off is that some cacti are susceptible to blowing over in strong windstorms.
Even the root system of a cactus plant is committed to the survival of the plant during long stretches when water isn’t available. The root network of a plant will grow when water is plentiful but die-off and shrink back toward the plant’s body when the plant can’t afford to spare the water required to sustain the wider root system.
While it is true that sending roots deeper would provide the plant with more stability, it would also require more energy to grow and more water to sustain. For most cacti, the extra stability just isn’t worth the expenditure of vital resources. Cacti get a better return on their investment by keeping their roots closer to the surface where they can soak up every drop of rainfall possible.
This article has outlined the numerous ways that cactus plants have evolved and adapted to be the premier specialists at water conservation in the plant world. The evolutionary tricks that the cacti have picked up throughout history incorporate the leaves, stems, stalks, and roots. It is a team effort when it comes to being efficient at water consumption. That is what it takes to thrive where few other plant species can survive, and that is what set cacti apart from most plants.
If you want to add more greenery to your apartment, office, or home, then you can’t go wrong with a cactus. You won’t have to worry about getting someone to water your plants while you’re on vacation or what will happen to your office décor if you’re traveling for business for a week or two. And now that you know how rare cactus blossoming is, you’ll appreciate the beauty of their flowers that much more.