Many people thought that cacti need just a small amount of water because they are accustomed to desert conditions. Is this true? How long can a cactus survive a prolonged drought? Given this, I did a 1-month experiment to answer this question once and for all!
Cacti cannot survive indefinitely without water. Test conducted on cacti demonstrates that after four weeks without water underwatering signs such as 1) shrinking, 2) discoloration, 3) wilting/leaves curling, and 4) dead brittle roots will appear. Cacti can survive without water from a few weeks to a few years.
You are probably wondering if you can just leave your cactus sitting near the windowsill or office table without water. Here, you will understand what could go wrong if you underwater your cactus. Have a good look at the experiment results.
First collected four cacti of two different varieties. It is crucial to select well-watered, no wrinkle, and actively growing samples for an accurate analysis. The experiment was performed inside my greenhouse, hosting hundreds of cacti.
The four cacti used for this experiment belong to the following species:
1- Pair of Gymnocalycium Mihanovichii ‘Chin Cactus’ – prefers regular watering, especially on hot days.
2- Pair of Haworthia Fasciata ‘Zebra Plant’ – do not like a completely dry substrate.
Each variety comes in identical pairs, one as the reference/control sample and the other as the test sample. Having this setup is vital to detect the changes and analyze the effects of underwatering easily.
The sample specimens are placed next to each other and were set up somewhere inside the greenhouse. The two specimen varieties have almost the same light preference, indirect/light shade.
In this setup, the test and reference samples can receive the same amount and duration of sunlight with water as the only independent variable. For one month, the control samples are watered regularly, while the test samples did not receive any water except the humidity in the surrounding. The arrangement stays in the same spot for the entire experiment duration.
To document any developing signs, I took photos of each sample every week or every time I can spot any changes.
The underwatering signs in cacti, like the Zebra Plant, are 1) closing/erecting leaves, 2) wilting tip, and 3) darkening of leaves 14 days from the start of the experiment. These signs of underwatering became more evident on the 28th day of observation.
The result indicates that the Zebra plant is vulnerable to changes in its optimal watering routine.
Closing/Erecting Leaves: At the start of the experiment, the test sample has some leaves spreading from the base. But after two weeks of no water, the leaves are becoming erect and gradually close up. The closing of leaves is caused by water loss in the plant’s system. In response, the leaves curled up to lessen transpiration.
Wilting Tip: Another noticeable sign of underwatering is the brown tips of the leaves. During moisture loss, the tip of the leaves is likely the first to wilt because of its small surface area.
Darkening of Leaves: The Zebra plant has light green leaves from the start. However, after 14 days, the leaves turn a bit darker/dull in color. This is another indicator that your plant is stressed and needs moisture.
While these underwatering effects are noticeable in the Zebra plant after 14 days, other signs like shrinkage, discoloration, and spine changes are evident in the Gymnocalycium Mihanovichii cactus after 21 days. It shows that Gymnocalycium is a bit more resistant to underwatering compared to the Zebra plant. It is because Gymnocalycium has thicker stems that can store more water.
After around three weeks without water, the body of cacti such as the Gymnocalycium develops wrinkles from the base. It grows dry as the water in its system becomes depleted, depriving the plant of moisture. Due to insufficient water, it becomes parched, and the body begins to wrinkle and shrink.
The lack of water affects the color of the cactus too. There is an apparent change from greyish green to greenish-black and yellow due to stress. Also, the spines grow longer and thin with noticeable discoloration (brown-light brown) due to dryness.
All distinct changes in the appearance of the test samples are mentioned and explained already. How about the root system of the plants? Let us take a look at how the root system reacts with the lack of water.
Although cacti have a unique way of absorbing moisture through their stems, their roots are the primary gateway in acquiring water from the substrate. At the end of the experiment, all four samples were uprooted to check the condition of the roots.
I inspected the roots thoroughly, and I found out that the test samples have the same status.
The lack of water can kill the cacti roots. The roots of Zebra Plant and Gymnocalycium test samples after a month without water have shown dead parts, all dried out, with no visible growth.
Cacti cannot live entirely without water because it is crucial for photosynthesis. Nevertheless, cacti have unique adaptations to extreme environmental conditions to survive months or even years of drought.
According to Arizona Sonora Desert Museum, most cacti develop an adaptation called succulence that helps them thrive for long periods without water. They are well-designed to endure dry seasons by utilizing the water that they store within their succulent stems.
The idea that all cacti require only small parts of water is just a myth. Cacti love to drink enough water to fill in their spongy stems for storage. On the contrary, they don’t like sitting on the wet substrate for long as it may cause root rot.
Underwatered cactus develop signs of 1) shrinking, 2) discoloration, 3) curling of leaves, and 4) brittle roots. Take note that some of these signs are common for overwatering as well. The main distinguishing hint is dryness.
Your dehydrated cactus will exhibit shrinking or shriveling due to insufficient moisture in the plant’s tissues. The stored water was all used up, and as a result, your plant will develop wrinkles, distorted, and uneven growth. This is mainly a common sign of underwatering.
If your cactus has a significant color change, it might be a sign of underwatering. When your cactus turns from green to darker color, it shows that your cactus is stressed due to the rapid evaporation of water from its stems.
While a yellow coloration indicates that your plant is not producing chlorophyll as they usually do because of an insufficient moisture supply. It may also be because of dried or dead roots experiencing extreme dryness.
Careful when assessing the discoloration as it might be associated with overwatering or lack of light. The simple indicator is when the cactus is mushy or not. Mushy discolored cactus might be signs of overwatering.
Lack of water may cause the leaves of your plant to curl up. Because they have not received the right amount of water, they will try to retain and squeeze in the moisture left in their system to conserve resources.
Wilting tips usually happen when water becomes unavailable for several days. The leaves began to turn brown and become brittle due to dehydration.
Another wise method in determining if your cactus is dehydrated is by uprooting your beloved plant. Cactus roots that are not getting enough hydration from the soil will become dry and dead. It will also come off easily when touched.
Fixing a shriveled cactus is easier than reviving a mushy one. Indeed, in gardening in general, it is way easier to save an underwatered plant than an overwatered one.
Here’s what I always do to restore my underwatered cactus:
1) Bottom soaked watering. If you notice some wrinkles or shriveling in your cactus, just use the bottom-soaked watering technique. In this case, you should:
- Prepare a basin filled with tap water, then submerge the shriveled cactus into the tub. The pot should have a bottom hole for the water to get in and soak up the potting mix. Allow the planter to sit in the water for 30-45 minutes. For severely dehydrated cactus, you can let it sit for three days straight.
- When the topsoil is already wet, remove the pot from the basin and let it drip to drain. After all the water from the substrate drains, put the cactus back to its original location.
You can magically see how your shrinking cactus will plump up after getting the right amount of water it needs.
2) Uproot and Trim Dead Roots. If there is no progress with the bottom soak watering, try uprooting your cactus and check for the roots. Dead roots might be the reason why your cactus is not plumping up after soaking.
After uprooting, remove dead and dried roots, then wash the roots to remove unwanted pests. Trim off some of the roots to stimulate new growth.
3) Repot To A Fresh Potting Mix. After trimming the roots, air dry the cactus for a day and replant it on a new pot and potting mix. Don’t let it sit under direct sunlight; instead, put it in a bright, shaded spot. Avoid watering for one week to prevent root rot. You can start introducing a small amount of water after a week and gradually increase for the following weeks.
4) Prune Severely Dehydrated Cactus. With a sterile and sharp knife, cut off the dead or desiccated portion of the cactus. Dead and dried cactus parts are unlikely to plump back to their original shape.
Cacti have special physiological modifications that equip them to withstand harsh situations such as water scarcity. They have unique adaptations from their roots up to the stems, spines, and stomata.
BBC Bitesize KS2 in England said that a cacti expert once explained how a cactus thrives for years amidst heavy downpour by relying on the water it stores. He reveals that an eight-month dead cactus still has water in its body tissues.
One impressive characteristic of the cacti that makes them survive without water for longer than other plants is their shallow roots. Its long and shallow roots spread out from the base to absorb moisture.
The roots tend to expand to take in all the water available in the substrate or the ground. In the dry season, the roots retract so that the cacti can preserve water as much as possible. Because of this ability, the cacti will remain hydrated as long as the water is in their system.
The water from the roots is absorbed into the cacti’s thick and spongy stem tissues for storage. Their stem tissues are composed of slimy mucilage cells, which binds to the water and inhibits evaporation.
As the stem absorbs water, its collapsible water-storage cells expand to retain more water until there is hardly any water to soak. Around the stem are the minute openings called stomata. These stomata are sunken and open only during the night to slow down moisture loss due to evaporation in the daytime.
Cacti can endure drought also because of their specialized leaves called spines. Contrary to other plants that lose moisture through leaf transpiration and evaporation, the cacti spines do not give off the water but retain it.
Its dense hairs and bristles limit airflow and protect the stem of the cacti from intense sun rays to avoid water loss or dehydration. In addition to water retention, the spines protect the cacti from predators who attempt to damage their water resources.
Cacti have a thick, waxy epidermis called cuticles that surrounds the stem.
Moisture cannot pass through waxy skin. The cuticle serves as a protective barrier preventing the water from evaporating from the cactus. It also inhibits the entrance of pathogens from the outside.
A cactus can live for several months or years, depending on its size and water retention ability. Many cactus explorers said that a giant desert cactus could survive for two years without rain in the arid land.
Most cacti are spherical, cylindrical, or semi-cylindrical in shape. Consequently, as they increase in size, their body volume increases significantly compared to their surface area.
Therefore, a giant barrel cactus can tolerate drought better than a tiny one because the volume of water storage per water loss surface is greater for the bigger-sized cactus. Small cacti seedlings are more prone to dehydration than mature larger cacti.
- Cacti can survive prolonged periods of drought, but they still need water to replenish their thirsty stems.
- Cacti have several adaptations that help them tolerate dry conditions. They can retain water because of their shallow roots, thick stems, spines, and waxy skins.
- An underwatered cactus can have a bigger chance to survive compared to an overwatered cactus.
- Larger cactus are more likely to survive prolonged drought than small size cactus.
- “The Giant Saguaro,” Arizona Sonoran Desert Museum
- “How cacti survive without water.” BBC BiteSize
- “Micrograph of Plant Cells and Tissues,” by James D. Mauseth, University of Texas
- “Growing, Connecting, Educating,” University of Arizona
- “Cacti and SUcculents,” University of Nevada, Las Vegas
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