It’s no secret that cactus plants can withstand quite a bit of drought and sunshine. But just how much sun do cacti need? And should they always be exposed to direct sunlight?
Of course, not all cacti are the same, nor do they have the same light requirements, but for the most part, all cactus plants enjoy basking in the sunlight.
In what follows, you can read about the general light requirements of desert cacti including tips on where to position your cactus plants for best light exposure, and some of the signs of excess light and the signs of too little light.
How Much Light Do Cacti Need?
Desert cacti thrive in lots of light, warmth, low moisture and good draining soil. These plants have evolved to retain water in their roots and stems and withstand arid conditions that are typical of the desert.
This means that sporadic rains don’t seem to be a problem for these plants. Because cacti plants are all about survival and adaptation to difficult conditions, they are slow growing plants.
On average, cacti prefer around 12 hours of light per day, but need a minimum of 4 hours of light per day.
These plants don’t enjoy being in the shade, so it’s important to find the brightest spot you have in your home, so that they get enough sunlight.
Don’t expose your cacti to more than 14 hours of light per day. While cacti can withstand a lot of direct sun, they are not immune to damage from excess sun exposure.
Desert cacti will thrive in direct sunlight, but tropical cacti will prefer indirect sunlight, and some species will actually do better in partial shade.
It’s important, therefore, to find out as much as you can about the light requirements of your chosen variety, so you can recreate as faithfully as possible the light conditions these plants receive in nature.
Where to Place Your Cactus Plant?
If you don’t really have a bright location in your home, you’re going to have trouble growing healthy cactus plants.
Ideally, you should pick a south-facing window, which will ensure that your cactus is getting all the sun it needs.
An east or west facing window will not provide desert cacti with enough sun exposure, but it may be a good choice for other cacti species that don’t require direct sunlight and do all right even in partial shade.
Therefore, if your particular cactus variety requires lots of light, before moving your cactus to the location of your choice make sure that your plant will get the sun exposure it needs there.
Signs That Your Cactus Isn’t Getting Enough Light
Lack of enough sunlight can produce a few symptoms that are easy to detect on your cactus plant.
Some varieties will become ‘leggy’ and stretch towards the light. The scientific name for this phenomenon is called etiolation and it’s irreversible, even though you change the environment of your plant.
Growths that are a result of etiolation can be pruned or clipped of, depending on your cactus variety.
Other cacti will become discolored. Deep green cacti will become a pale green, so changes in the color of your cactus is an easy-to-notice symptom.
While root rot is usually a consequence of overwatering, it can also be tied to lack of light issues. With little sun exposure, the soil dries out much slower, keeping the soil too moist.
A cactus that’s growing more on one side than the other also exhibits signs that it is not getting enough light. When this happens, it means that one side is getting more light than the other side. The solution to this issue is to periodically rotate the plant so it gets enough light on all sides.
If you move your plant to a new location where it will get more light, do it gradually, so that the plant gets accustomed to its new location and doesn’t get scorched by sudden sun exposure.
Signs That Your Cactus Is Getting Too Much Light
If your cacti get over 12 to 14 hours of light per day, they may experience distress because of excess light.
Signs of too much light include:
- Bleached aspect, yellowing or stem turning orange
- Brown spots or callousing
All these can happen if a cactus that’s been sitting in partial shade or indirect light gets moved to a location with direct light.
Too much light will also interfere with the CAM (Crassulacean acid metabolism) photosynthesis of cacti plants. The CAM photosynthesis allows the cacti to open their pores during the night when temperatures drop to reduce loss of moisture.
Cacti will then take up carbon dioxide, which is needed for the photosynthesis that goes on during the night.
Can You Keep Cacti Outside?
During summer, I like to move my cacti outside, where they can bask in the sunlight, but I always move them back when temperatures start to drop. Usually, cacti don’t do well once temperatures hit the 50 F mark.
There are cacti that will tolerate temperatures lower than 50 F. For example, the green flowered hedgehog cactus (Echinocereus viridiflorus) can withstand 20 degrees below zero Fahrenheit.
Depending on the climate in your area, you may be able to keep some cacti outside all year long.
Therefore, periodically moving your cacti outside during the summer will be beneficial to them, but it’s important to gradually familiarize them with any changes in light conditions, and to move them back inside once temperatures start to drop.
Cactus plants — and many other succulents too — require direct sun exposure to thrive. But not all cacti species have the same light requirements, therefore, make sure you know the light requirements of your cactus species to help it develop normally.
When a cactus enjoys direct sunlight, it doesn’t mean it will do great for any amount of time in direct sunlight, or that they don’t ever get sunburn.
The key is to always monitor the health status of your cactus for signs that will let you know if it’s getting too much or too little light.