Succulents, including cacti, thrive in warm conditions but are quite sensitive to changes in their surroundings. You can tell by looking at them; they might change color or shape if something’s off.
For example, if your cactus is turning red, it’s probably because it’s getting too much sun, especially the harsh afternoon light. This red color is the cactus’s way of trying to take in less sunlight.
Most plants, cacti included, have cells containing anthocyanins. These are red and other colored pigments that help the plant shield itself from harm or serve other functions.
If a cactus gets too much sun, it produces red anthocyanins. This reduces the green chlorophyll in its cells, preventing damage from too much UV light.
This issue is common in spring. After a winter with short days and less sun, a cactus adjusts to those conditions. Come spring, with its longer, brighter days, the cactus might not adapt quickly enough. So, it makes red pigment for protection.
Moving your cactus from indoors to outdoors in summer, or from an east to a south window, can trigger this. Not all cacti turn red with light changes, though. Some are very sun-tolerant and don’t react this way.
Cacti generally need 6-8 hours of direct sunlight. If you’re moving it to a sunnier spot, start with partial direct light, like half a day, or slowly increase its exposure. Ideally, it should get morning sun for six hours and light shade afterwards. Gradually up the sun exposure until your cactus can handle a full day without turning red.
Lack of water can turn not just cacti but other succulents red too. They also tend to shrink and get wrinkly.
In a drought, a cactus changes color as it cuts down on photosynthesis to save water. This reduction in chlorophyll makes the color shift towards reddish or brownish-green.
To see if your cactus needs water, check the soil moisture. If it’s dry, it’s watering time. Remember, pots on sunny windowsills can dry out fast in hot weather, so it’s important to check regularly.
A sudden change in temperature, either up or down, can make a cactus turn red. Like before, the plant produces anthocyanins, which help slow down cell damage from oxygen.
Temperature changes can happen for various reasons. If a cactus is outside and there’s a quick drop in temperature after a hot day, it’ll get stressed and change color.
Usually, cacti prefer temperatures between 50°F (10°C) and 85°F (29°C). Going outside these ranges can stress them. If your cactus turns red due to temperature shifts, it should recover after some time.
Root rot might also turn a cactus red. Along with this, the plant might shrivel and emit a bad smell near its base. This often happens with too much watering or using the wrong type of soil.
If root rot is the issue, first stop watering. Then, take the cactus out of its pot and clean off all the soil from its roots. Use a sterile tool to cut away the rotten roots, being careful not to harm any healthy parts.
After removing the rotten parts, treat the cuts with hydrogen peroxide or a fungicide. Then, replant the cactus in fresh succulent soil in a pot with good drainage.
Keep the pot in shade and avoid watering the cactus for a few weeks. Start watering lightly later on. If the cactus begins to improve, you can gradually reintroduce it to direct sunlight.
Plants need magnesium for photosynthesis along with nitrogen, phosphorus, and potassium. If there’s not enough magnesium, photosynthesis slows down. This can make a cactus turn a pale reddish-green and its leaves might start to wilt.
Magnesium naturally occurs as sulfate. In the wild, plants usually get enough from the soil or water, so they rarely lack this element. However, at home, the specially prepared soil for cacti might not have enough magnesium.
To fix this, you should use a magnesium fertilizer. You can choose a compound fertilizer that includes all the necessary elements, or you can add magnesium directly.
You’ll find many suitable products at garden stores. Using these, your cactus should not only return to a healthy green color but might also grow better