A purple cactus can be caused by many factors. Some cactus naturally turn purple, but it can also be a sign that something is wrong. Find out why your cactus is turning purple so you can help it thrive.
In most cases, cactus turning purple in response to environmental stress. Too much sunlight, temperature problems, root rot, nutritional deficiencies, crowded roots, and cactus cysts are all possible causes. Additionally, your plant may be perfectly healthy and is simply adjusting to new conditions.
Is A Purple Cactus A Cause for Concern?
If your cactus is turning purple, this isn’t always a sign of a major problem. For some types of cactus, it’s normal to turn a bit purple.
This is a natural part of their life cycle when they experience cold, dry conditions.
Could It Be Fruit?
If you have a Prickly Pear cactus, you could be in luck. There’s a chance that the purple spot on your cactus is actually a fruit!
Prickly Pears are sweet fruits that are used in a lot of Mexican cuisines. They range in color from green to reddish-purple and can resemble a discolored spot on the cactus.
Causes of Cactus Turning Purple
A change in color becomes a cause for concern if many of your cactus’ leaves are noticeably purple.
Other signs of a problem include wilting, stunted growth, or soggy foliage. It’s important to determine the cause of the color change to determine if your plant is in any serious danger.
Cacti change colors when they experience stress. Cacti contain a purple pigment called betalain, which they produce more of as a stress response.
Let’s go through the potential causes and figure out how to treat them.
Too Much Sunlight
Even though cacti evolved to do well in bright sunlight, the one you have at home might be having trouble adjusting.
Store-bought cacti have usually been grown under shade in a greenhouse. This means that they aren’t used to so much direct sunlight.
Cacti need bright light, but it’s best for the light to be indirect and dispersed. Suddenly exposing a cactus to bright light can scorch its skin, causing it to turn a purplish-red color.
If your cactus is new, or if you have recently moved it to a sunnier spot, there’s a good chance that it’s sunburnt.
How to Treat Sun Scorched Cactus
Luckily, the fix for sunburn is relatively easy. Move your cactus over to a spot that gets less direct sunlight.
Don’t go moving it to your basement just yet though — cacti still need a whole lot of sun!
Light that falls directly onto the plant, for example through a south-facing window, is direct sunlight.
The other windows in your house will offer indirect sunlight, which is more dispersed and easier on the plant.
Moving your plant over to a window facing in any other direction can help with sun scorching.
If you only have south-facing windows, try making a DIY sun filter. Simply prop a paper towel up over your cactus to give it some much-needed shade.
Temperature Issues
Purple leaves can be a sign of temperature-related stress. Cacti sometimes turn reddish-purple when their roots overheat.
Cacti can also turn purple when they get too cold. If the plant is suffering freeze damage, its cells burst and it is no longer able to hold liquid.
How to Fix Temperature Stress
The ideal temperature is somewhere in the middle, so it’s important to avoid placing your plant in extreme temperature conditions.
To prevent your cactus from getting too cold, keep it away from drafty places like open doors and windows. Also avoid places that get too hot and dry, like fireplaces and heating vents.
Since the plant’s roots are the most likely to overheat, keep your cactus in a pot that stays cool. Avoid black plastic planters, and instead go with a material like clay.
Root Rot
Purple leaves could also be a sign of root rot, which results from overwatering and poor drainage.
If the soil stays wet for too long, your plant’s roots will die and will be unable to take in any more water and nutrients like magnesium. As a result, your cactus may turn purple.
How to Fix Root Rot
Begin by pruning off the damaged roots and leaves with sterile scissors, and removing as much of the soggy soil as you can.
Transfer the plant into a sterile pot with fresh potting soil. Don’t water the cactus for a few days after moving it, and let the top inch of soil dry out between waterings.
Most of the time root rot is the consequence of overwatering. I have written an article on how you can save your overwatered cactus. Also, you will learn how to water them correctly.
Nutritional Issues
One possible reason why your cactus is turning purple is because it doesn’t have the proper nutrients that it needs to survive. If your plant is wilting and turning purple, this may be a sign of a magnesium deficiency.
Christmas cacti are particularly likely to develop magnesium deficiencies. That said, all types of cacti are susceptible.
How to Treat Nutritional Issues
If your cactus is experiencing a magnesium deficiency, fertilizer is the solution. You can buy a magnesium-enriched fertilizer, but you can also go the DIY route with an Epsom salt treatment.
To make a magnesium treatment, mix the following ingredients into a spray bottle:
- Eight tablespoons of Epsom salts
- Two and a half gallons of water
- One or two drops of dishwashing detergent
Use a spray bottle to spritz the leaves of the cactus, making sure to also get the undersides of its leaves. Keep using the spray mixture every two weeks until your cactus turns back to its normal color.
Crowded Roots
Crowded roots are another potential reason for your cactus’ color change. If a plant is grown in a container that is too small, its roots can become overly crowded, or “rootbound”.
Rootbound plants are unable to properly absorb water and nutrients from the soil. The nutrient deficiency can cause the leaves to turn purple as a stress response.
How to Fix Overcrowded Roots
With time your cactus root system will also grow bigger and it may not fit within the pot it used to be.
If you notice that some parts of the roots are trying to get out through the drainage hole then it’s time to repot your cacti to a bigger container. Normally consider repotting your cactus every 3-4 years.
If your cactus’ roots have become overcrowded, you’ll need to move it into a bigger home. As a general rule, you should repot cacti when you can see their roots through the drainage holes at the bottom of the pot.
For faster-growing cactus varieties, this generally takes two to three years. Slower growing cacti should be repotted only about every three or four years.
Not all species of cactus have the same needs, so it’s important to research the ideal conditions for your cactus.
For example, some types of cactus such as Christmas cacti actually do well when they have crowded roots.
For this reason, a Christmas cactus should not be repotted unless it has been in the same pot for at least a few years.
Here are the steps to repot your cactus:
- Before repotting your cactus, first, make sure that you’re wearing thick gloves to protect your skin from the plant’s sharp spines.
- Check the plant and soil for any pests or signs of disease
- Select a new container one size larger than the previous one
- Place gravel at the bottom of the pot to help with drainage, and scatter a thin layer of gravel on the surface of the soil
- Let the soil drain out before resuming your regular watering schedule
Source: Cactus & Succulent Society of San Jose
Cactus Cyst
A purple cactus could also be a sign of an infection. There’s a chance that your plant is infected with a pathogen called Cactodera cacti, more commonly known as cactus cyst.
Cactus cyst happens when a cactus is planted in infected soil. Reddish-purple leaves, as well as stunted growth and wilting, are all possible signs of infection.
The most obvious sign of the cactus cyst, however, is tiny white spheres that appear on the plant’s roots. (Source: Plantwise Knowledge Bank)
You May Also Enjoy: Black Spots on Cactus (How to Treat, Identify and Prevent)
How to Treat Cactus Cyst
It is very difficult to treat the cactus cyst once it has infected the plant, so it’s better to focus on prevention instead. To prevent your cactus from getting sick, plant it in clean, sterilized soil in a new pot.
If your cactus does get infected, your best bet is to discard the plant. As hard as it is to throw away your beloved cactus, it’s important to prevent the infection from spreading to your other plants.
Have you ever dealt with a cactus that is turning purple? What caused it, and what did you do to revive your plant?