Do Cactus Plants Need Sun?

The cactus is a beautiful low-maintenance plant that can be found in many different places across the globe, but what do you need to know about caring for this desert-dwelling plant? One of the most important things to consider when growing a cactus is access to sunlight. Do cactus plants need sunlight? The answer may surprise you!

do cactus need sun
“Cactus” by Richard Leeming is licensed under CC BY-SA 2.0

Do cacti need sun?

Cacti love the sun. There are a few exceptions, but otherwise, they prefer to get as much direct sunlight as possible. Are they more beautiful in a different place in your house? Then it may be that your cactus is not really happy.

How do you recognize that your cactus is getting too little light? Cacti do not grow quickly, so you often only notice later if they are not happy in a place. Still, there are some signs you can spot before it’s too late and your cactus has given up with grief.

A cactus that is too dark will always look for more exposure to light. And in the meantime, to save energy, the new growth will be distorted and weary. The growth is not nicely round and full, but thin and elongated, maybe even pointed in a bulb cactus.

That is a sign that the cactus is looking for more exposure to light. Sometimes this growth is very fast because a cactus wants to find exposure to light as quickly as possible. Unfortunately, that growth spurt is not good for your cactus at all, although you may at first think that it is going well.

This process is called etiolation, where your cactus often turns a bit yellowish as well, instead of deep green. You will get weak and unhealthy plants.

Some examples of this are a cactus that used to be a ball, but now suddenly becomes elongated with a narrow point at the top. An opuntia (that cactus with ‘rabbit ears’) whose new ‘ears’ grow tall and thin. A cactus with an unhealthy light green color, or a cactus that hangs a bit limply.

do cactus need sun

How much sunlight does a cactus need?

A very bright place without intense sunlight with at least 3,000 lux is well suited for all cacti. The following applies to cacti: the lighter the better. Many species of cactus can tolerate the blazing midday sun even behind glass.

The easiest way to determine whether the location you are considering or already selected is fair in terms of the exposure of light is with a commercially available lux meter, a measuring device for the intensity of light. It is important that the measuring range covers at least the range between 700 and 5000 lux and that a reasonably reliable and accurate reading is possible. Such devices are available either in garden supply stores or online.

If you have a hand-held exposure meter for photographic purposes that allows the light measurement, you can also use this with sufficient accuracy: Set the film sensitivity to 18 DIN (= 50 ASA). The following assignment of the exposure of light values ​​(also called EV = exposure value) to the illuminance results. In addition, a shutter/aperture combination is specified, as not all hand-held exposure meters display light values.

Light valueAperture / timeIlluminance
71/4 s at f. 5.6= 700 lux
81/8 s at f. 5.6= 1400 lux
91/16 s at f. 5.6= 2800 lux
101/30 s at f. 5.6= 5600 lux

You should take the measurement on a normal day in the morning or in the afternoon when the sky is slightly overcast. At noon you would receive values ​​that mislead you into thinking that the circumstances are favorable.

Measure exactly where the cactus is or should be. It is necessary that you measure not only at the front of the window, where it is naturally the brightest but also as far in the interior as the cacti plant takes up space. Here you will experience some surprises!

You can also measure in the middle of the living room or in the corners of the room, which would definitely benefit from an optical enhancement with indoor plants. You will find that the illuminance there is usually so low that no cacti plant can thrive in the long term. Room artificial lighting should not be used on cacti, because the required high values ​​are usually not achieved. In addition, due to the mostly small space requirement, there is almost always a suitable spot in the natural sunlight.

do cactus need sun

Can a cactus get too much sun?

Yes, too much sun can damage a cactus.

When a cactus gets too much sun, it often turns bluish or sometimes reddish. Then you should protect it from the direct sun from now on. The process is reversible in the initial stage, ie the discoloration recedes over time. However, if you leave it in full sun, there are two options. Either it gets used to the sun slowly or it slowly dies.

Where to plant cactus?

Even if the cacti plant does not have a great need for water or soil, it still needs a lot of light to develop. Also, it is best to place it outside or near a south-facing window. On the other hand, consider placing it in a cool room when cold winter comes.

When planting in a garden, there are a few rules to follow to properly plant your desert plant in a suitable location. The best is a position where they enjoy bright sunlight part of the day, at least 5 or 6 hours of sun, in the morning or in the afternoon.

Large cacti tolerate more sun than small ones, but even when they reach 4-5 years it is advisable that part of the day they are under a slight shade. Protect young seedlings. The soil in dark plastic pots can overheat in the sun and burn the roots of the cactus. It is best to have pots of white or vibrant colors. If you have no other option, cover the outside of the pot with paper or other thick white material.

For indoor cactus plants, however, try to take them out on a balcony during the summer season, so that they can enjoy a few hours of sunlight and a consequent renewal of air. If the light in your interior is low, that’s okay! Opt for cacti that come from the equatorial forests, like the Schlumbergera which offers magnificent flowers.

how much sunlight does a cactus need

Cacti that don’t need sun

Epiphytes

Some species need to be protected from direct sunlight in the hottest part of the day. These are the epiphytic species (which grow on other plants without parasitizing them) that grow in tropical forests at the foot of trees that form a shady canopy.

Among the epiphytic cacti, we find:

  • The Schlumbergera, which we will take care to keep away from direct sun by placing it on a table or by interposing a curtain between the cactus and the glass window.
  • The Rhipsalis species includes about thirty epiphytic cacti native to the forests of South America (there are some in Africa too) and which do not resemble other cacti: few or no thorns but pretty drooping stems that love shade and humidity.
  • The Epiphyllum or Disocactus family are perhaps the most beautiful species of epiphytic cacti. They are satisfied with a little shade, but their culture is complicated in our latitudes.

Read also:
Best Gloves for Handling Cactus

Shade tolerant cacti

Here are two species of cacti (there are very few) which are not epiphytic and which can be satisfied with a little shade if you live in an apartment, in a studio with little light for example.

  • Gymnocalycium : cactus from a family that includes more than fifty species from South America. It is nicknamed the “spider cactus” or “chin cactus” because of the shape of its needles. It can be stored in a very small pot; an advantage for the amateur who lives in the studio. Easy to maintain, it can withstand insufficient light, such as Gymnocalycium mihanovichii or Gymnocalycium stenopleurum .
  • Copiapoa : a genus of cactus from Chile comprising about 25 attractive species, some having the shape of cacti cacti, others rather spherical. Its sides which sometimes grow diagonally and lined with thorns. They ask to be protected from the full sun of midday in summer.

What to do when a cactus becomes etiolated?

Okay, you’ve recognized the problem and want to do everything you can to give your cacti plant a better future. With enough light, for example in a nice spot on the windowsill. Don’t expose your cacti plant to excessive sunlight all at once, but let it get used to it a bit. If you move it a little closer to the window each time, you have less chance of sun damage from the sudden amount of intense light.  

A better spot does not mean that the thin growth will suddenly become full. The cactus will grow wider above the thin growth, giving you a uniquely shaped cactus. 

With some cacti, you can easily remove the deformed growth, for example by cutting off the deformed ‘ears’ of the Opuntia. Others will continue to bear the consequences of the little light. But at least you will see the life story of your cactus reflected!

Conclusion: Do cactus plants need sun?

Although all cacti need long hours of light in general, not all can withstand the direct rays of the sun.

As a general rule, species with hairs, very strong spines or a large number of them, require lots of sunlight; while species with few spines and succulent plants require less intense sunlight. Ventilation is also very important for the latter.

“Cactus. Sun.” by amycgx is licensed under CC BY-NC 2.0

The right amount of exposure to light is perhaps the most difficult part of maintaining cacti. Especially if you live in a cold and dark country, you should make sure that your cacti receive adequate light, at least every now and then.

Cacti are naturally used to receiving long hours of light. Most cacti can survive with less or indirect light, but they will grow slower and will never bloom. During the summer, cacti usually receive more intense light than in winter. Most cacti actually need only a few hours of bright sunlight. Don’t forget to always place adult plants in cactus soil near windows.

It is also possible to provide artificial light to the cacti. Fluorescent lamps are an option as they provide plenty of bright light. The disadvantages are that these lamps provide little heat, and must be placed at a maximum distance of 10-30 cm above the cacti. Another alternative for artificial light is halogen lamps, which provide much more heat. HPS (High Pressure Sodium) artificial light are excellent, but the energy consumption is high.

Remember that too much direct light can also cause problems. If the cacti receive too much direct light, the side exposed to the hot sunlight will lose its true color, resulting in burns. This can cause permanent marks.