It is known that cacti can tolerate the harsh scorching sun and dry desert conditions. But can they survive the cold winter temperatures too? We tested it for you! We place cactus in the fridge (yes) and checked how well they withstand low temperatures.
In general, the majority of cactus can survive low temperatures down to approximately 37F (3C) with minimal cold damage for periods up to a month. However, some cacti (frost tolerant) can survive easily way lower temperatures. Prolonged cold exposure will cause 1) softened stem, 2) dull colour and 3) blackened stem.
Each cacti species has different cold tolerance. While other species can barely stand the typical cold, some can go beyond subzero temperatures and still survive after the winter period. Interesting, isn’t it? Stay with me, and together let’s get in awe of how cacti survive the severe cold.
Four cacti (2 pairs of shade-tolerant species) were used to carry out an experiment and test if they could resist the cold temperature. Each identical pair has 1 test sample and 1 control sample to determine any changes at the end of the experiment.
Here are the cacti species used in the experiment:
- 2 Golden Ball Cactus (Parodia ‘warasii’) – temperature requirement above 40F (4.5C)
- 2 Chin Cactus (Gymnocalycium ‘anisitsii’) – resistant at 23-32F (-5-0C) or less in a short period
Before the experiment, both test samples have apparent new spine growth, which signifies that they are actively growing. The experiment setup is done by placing the samples in clear plastic jars (with covers and tiny holes at the bottom) inside the refrigerator (not freezer) with a temperature of 37F (3C).
They stayed unwatered inside the fridge for one month. Weekly monitoring was done to document any changes. On the other hand, the control samples remained in the greenhouse and received the usual care.
Test results after 30 days showed that Gymnocalycium and Parodia test samples had survived the experiment. However, both plants have stopped growing new spines after the second week. The colour of the Gymnocalycium has become dull, while the Parodia develops soft stem tissues in the final week.
The test samples resisted the 3C cold temperature and thrived without water inside the dark fridge for a month. Although minimal changes were observed, we can tell that Gymnocalycium is cold-tolerant while Parodia is slightly resistant.
As long as the temperature remains above 3C and the soil remains dry, they can tolerate the cold winter season. They have survived because of their tendency to go dormant and stop their cell activity as the temperature drops.
Does The Lack of Light Affect The Experiment Result?
The absence of light inside the fridge does not create any effects on the experiment because the test samples are species that can withstand dark for a given period. Also, this experiment does not show signs of lack of light, such as the pale appearance associated with a stretchy stem.
The 3 most common signs of cold damage are 1) softened stem and 2) dull colour. However, hard frost can harm differently by freezing and disrupting cacti cells, leading to 3) blackened stems in just a matter of days.
The amount of damage a cactus can sustain is dependent on its species, the extent of temperature it experiences, the amount of time it is exposed to cold, and whether it is in its active state or not. Moist soil mix hastens the damage caused by decreased temperature.
Stems are likely to become soft once the cacti are kept too cool for an extended period. The cold temperature causes cacti cell membranes to decrease mobility and metabolism. It means the cacti become inactive, resulting in softened mushy stems.
At cooler temperatures, water and nutrient permeability decreases as well as cell respiration. The normal fluid flow within the different layers of cells on the cactus stem is affected, leading to water build-up inside. Having not used the moisture inside leaves the cactus stem soft to touch and soggy.
Further cold exposure can lead to stem rot and cactus death. However, if the cactus is removed from the cold as early as possible, the plant can still recover as long as kept dry in a well-ventilated and lighted spot.
Cold exposure can dull the vibrant colored cactus stem. Most cacti, even the cold-hardy species, gradually change colour during winter as cell activity decreases. The presence of green chlorophyll in the cells reduces as they become inactive, revealing only other colors.
However, this does not mean that the cactus is sick. It will revert to its original color once it is removed from the cold and exposed to the light gradually. Although there are cacti that can sustain this situation, some will succumb to death due to prolonged cell inactivity.
Extreme low temperatures can freeze cacti cells and cause irreversible damage. Black areas occur mainly on growth tips and pads, thin stems, and cactus ribs. The damage usually appears immediately after the freeze and it is permanent.
Frozen plant tissues generally appear dull green and turn white as they harden and freeze. During this state, the cacti cells are already dead because of dehydration. The sharp ice crystals puncture the membranes and leave open lesions on the stem.
As the temperature increases, the ice gradually melts, and the inside stem becomes water-soaked and transparent. Some moisture leaks from the wounds and allows fungi and bacteria to infect the exposed areas. Later, the affected portion develops rotting black patches.
Cacti living in regions with periodic cold survive the temperature drop by becoming dry and dormant. During their dormancy state, cacti stop growing and become less active. Reducing water intake allows the cells to release water and collapse to avoid freezing.
One unique adaptation of cacti to survive winter cold is becoming inactive and staying slightly dehydrated. As winter progresses, the plant will stop producing food, reduce water absorption or limit it to a minimum. The plant hardens its stems to prevent complete dry out while going dormant.
Some species even retract below the ground to avoid further moisture loss while staying alive throughout the winter. Retaining just a little moisture in their system prevents them from freezing and suffering from other potential damage.
Other cacti species such as Golden Barrel Cactus, Coryphantha, Trichocereus and Echinocactus develop extensive spines to withstand the biting cold wind. Species such as Opuntia produce thick waxy epidermis to endure frost. Oreocereus have thick wools that protect the stem from the harsh cold.
Cactus species that are not cold tolerant should be brought indoors when the temperature drops to avoid freeze damage. Cold-hardy cacti are fine outside in the winter but should be kept inside when temperatures drop below zero.
It is crucial to know the hardiness of the cacti species you are growing. In this way, you can know when to bring it indoors or provide some protection against frost. Some cacti thrive at subzero temperatures, while others barely withstand the average cold.
So, before growing cacti in landscapes and containers, check their hardiness if they can withstand extremely cold conditions. Here are some examples of frost tolerant, cold-hardy, and cold-sensitive cacti.
|FROST TOLERANT CACTI
(15 to 20F or -9 to -6C)
|COLD HARDY CACTI
(30 to 40F or -1 to 4C)
|COLD SENSITIVE CACTI
(45 to 50F or 7 to 10C)
|Prickly Pear Cactus
|Golden Barrel Cactus
|Silver Torch Cactus
|Golden Ball Cactus
|Sand Dollar Cactus
Cacti growing outdoors in the states such as Texas, Maine, and other regions that belong to zones 3-6 has a risk of cold damage.
When the temperatures get unpredictably harsh during winter, protect outdoor cacti from potential frost damage by1) using protective cover, 2) moving the plants indoors, 3) providing shelter, and 4) covering the topsoil.
If the temperature in your area usually drops below zero with episodes of frost, then it is essential to provide safety for your beloved cacti. The weather often becomes unfamiliar, and it helps to have advanced protection before it gets worse. Here’s how you can protect cacti in winter.
Frost efficient items such as burlap, thick plastic sheets, and frost cloth help keep frost from getting into the plants. This is a quick and convenient solution to keep cactus safe from the cold.
When setting up burlap and plastic sheet covers, one crucial thing is to leave enough space above the cacti. Make sure that the burlap cloth does not touch the cactus to avoid damage when the blanket gets wet. The plastic sheet can moisten and harm the cactus as well.
1. Frost Cloth– Good quality frost cloths can keep cacti warm for an extended period by retaining heat and preventing it from escaping into the chilly air. Likewise, the cloth helps to keep cold air out. White frost cloths are ideal, enabling light to pass through and reach the cactus.
2. Burlap Cloth– Burlap cloth is also a great covering because its breathable material allows good air circulation. Choose the thick fabric or double the layer for added protection if you have thin material.
3. Plastic Sheet– Thick plastic sheet provides shelter from frost, humidity and cold wind. You can use long sticks or poles for structure and pegs to fasten the cloth. Chairs with high backs can be used to set up covers for low growing cacti.
Here are some online items you can use for cover.
One sure way to protect cacti from the frigid environment and keep them dry is to transfer the plants inside. However, this is only applicable for container cactus and possible only for a few plants, as this can be a lot of work if there are several containers to bring indoors.
When moving the cactus inside over the winter, make sure to provide light, sufficient ventilation and keep the soil dry. Place the plants near a south-facing window or provide a grow light.
If the winter climate is not so harsh, but the air is chilly, provide cacti with some shield from the cold wind. Behind the walls, below the outdoor chairs and tables are good spots to shelter the plant from the cold climate.
If you are confident that the temperature will warm up and that your cactus will have plenty of sunlight during the day, then this can be a brilliant way to protect your cacti from mild freezes.
When the temperature drops, the warm soil gets cooled quickly. Covering the topsoil with a thin layer of stones such as lava rock or pumice can help keep the substrate warm.
A thin layer of wood shavings or rice hull mulch can also trap the soil’s heat and warmth. Just be careful not to use thick mulching as it can restrict airflow and trap moisture leading to root rot.
PRO TIP: Make sure to remove cloth and plastic cover, pebble toppings, and mulching after the threat of frost so the cactus can breathe and any moisture left will evaporate. Before moving back the plants indoors, you should not immediately expose them to strong sunlight to avoid sunburn.
Cacti can be at risk when exposed to ice or snow. When snow falls and stays long on the cold-sensitive, and even on the cold hardy cacti, the cells will start to get frozen and turn icy. The exposed part will rupture due to the ice and develop lesions which can be the threshold for fungi.
How cold a cactus can get depends on the species. Some species hail from the highland and cold desert climate can weather temperatures 0- 20 degrees Fahrenheit (-12 to -34C). These cacti have enormous spines and thick wools to keep the cold out.
Cold damage cacti can be revived as long as there are still some healthy parts. Prune the affected area and remove all the damaged parts to prevent the rot from spreading. However, you must wait for the winter to be over before saving your damaged plant. Or else, you’ll be risking further stem rot.
A cactus can tolerate the 37F (3C) cold temperature for 31 days by becoming dormant or inactive. It stops growing and producing food for the entire system. Water intake is minimal, and a lot of moisture is released as the cells shrink to keep them from freezing.
Cacti that are exposed to extreme cold can suffer minimal repairable damage like softened stem and dull body color. However, the freezing temperature harms cacti differently by developing black stems that rot afterward.
- “Effects of Cold Weather on Horticultural Plants in Indiana,” by Larry A. Caplan, Purdue University
- “Plant adaptation to frequent alterations between high and low temperatures,” by Guowei Zheng, Bo Tian, Fujuan Zhang, Faqing Tao, and Weiqi Li, National Center for Biotechnology Information
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