How Much Sunlight Does A Moon Cactus Need? [Too Much or Too Little]


Moon cactus is just a kind of finicky as it is two distinct cacti grafted together with different cultivation needs. One example is their differences in light requirements. So, how much sunlight does a moon cactus need?

A moon cactus needs at least 4- 6 hours of indirect sunlight and prefers a bright, shaded spot with morning or afternoon sunlight daily. Well-balanced light exposure is required to keep the moon cactus thriving, maximizing its life span.

Inadequate light is the most common reason limiting the growth of a moon cactus. However, too much light can be harmful to the plant as well. Then, what is the appropriate light requirement of a moon cactus?

Moon Cactus Light Requirement

In case you don’t know, the moon cactus is a combination of two cacti. The top portion uses a Gymnocalycium mihanovichii mutant cactus, while the bottom uses another cactus, usually a Hylocereus species. These two species are grafted so that their vascular tissues will come in contact and eventually merge.

The two species which made up a moon cactus have different light necessities.

Gymnocalycium Mihanovichii (the Head)

A moon cactus’s scion (a botanical term for the top graft) is a Gymnocalycium mihanovichii obtained through human selection (a bit like the dozens of different dog breeds). It comes in highly pigmented shades such as yellow, pink, red, orange, and sometimes purple. The mutant cactus heads have a way lower chlorophyll level leaving them defenseless against the sun radiation.

Its chlorophyll-less body cannot withstand prolonged direct sun exposure. Long hours of direct sunlight will cause sunburn and discoloration on the cactus. Indeed, most moon cactus are kept indoors, placed either near a bright window sill or inside a greenhouse.

Hylocereus Species (the Rootstock)

The colored scion is grafted to a green rootstock as a source of its nutrients. Common rootstocks are the robust Hylocereus species. It is rich in chlorophyll and can store enough water to supply the whole plant.

This part of the moon cactus, however, requires sufficient light needed to manufacture its food. It prefers direct sunlight without being scorched due to its thick, green flesh absorbing light and energy. The rootstock can tolerate several hours under full sun, and they sure love it.

Ideal Sunlight Exposure

Moon cactus is a very complex plant when it comes to sunlight exposure.

Since both parts of a moon cactus have different light preferences, balanced sunlight exposure is necessary. Place your moon cactus in a bright shade where it can receive 4-6 hours of indirect slanted sunlight daily, depending on your location.

In that way, the scion will not burn, and the rootstock can absorb enough light as well. Be mindful when choosing a spot for your moon cactus. Remember, the ideal location of your moon cactus for decoration may not be a perfect spot for its growth.

Ideal Indoor Location For Moon Cactus (Windowsill?)

Ideal Spot for Indoor Moon Cactus

A room with natural light is the best spot for a moon cactus to receive sufficient sunlight.

Growing a moon cactus inside your home with natural sunlight coming in is ideal. Placing your moon cactus near a south-facing or east-facing window sill of your home or office is the best. In the same way, it can absorb at least 2 hours of morning or afternoon sun and 4 hours of bright light for the rest of the day. That is enough for the moon cactus to absorb energy from the sun needed for photosynthesis.

Grow Light

Like other plants, the moon cactus needs light to provide energy for food production. Moon cactus in greenhouses or near window sills absorb balanced wavelengths of light coming from the sun. However, there are settings when natural light is not sufficient. Like when you live in an apartment or dormitory with little to no sunlight.

Artificial or grow light will be fine if you cannot provide natural sunlight for your cactus. These grow lights are designed to emit supplemental light wavelengths suitable for plant growth.

When purchasing a grow light, always consider the color temperature, light intensity (lumen), type of bulb, and power consumption. This grow light on Amazon has a specification that provides an acceptable spectrum and light intensity needed by a plant to grow indoors.

The grow light below it serves pretty well:

The 3 Signs Of Light Deficiency

Moon cactus without light for several days will not die immediately. However, there will be changes in their structure and color. It will show on their appearance if they are deprived of light. And if that happens, you need to take action to avoid killing your moon cactus. Here are the possible signs of light deficiency in a moon cactus.

Etiolation/ Stretching

Etiolation happens when the moon cactus is desperately searching for a light source. It stretches out from the growing point at its center. An etiolated cactus develops an elongated growth from the tip. The once spherical moon cactus will become cylindrical.

Keeping a moon cactus in a spot with little to no light will result in etiolation. The etiolated moon cactus will not die immediately, and saving the plant is possible. Just provide enough sunlight, and your moon cactus will smile once more.

Paleness

Etiolation is usually accompanied by paleness. If the moon cactus cannot receive enough sunlight, photosynthesis will fail. The plant cannot produce enough food for its system; thus, new growth has unhealthy color.

Bringing your moon cactus gradually to a bright, shaded area will get back its vibrant color.

Root Rot

Without light, a moon cactus cannot synthesize food affecting its energy level and water absorption capability. The tendency is the soil will remain moist for too long and can be a breeding ground for fungus. A fungal infestation will result in rotten roots.

The 3 Signs Of Too Much Light

Indeed, the moon cactus is too tricky with light requirements. Low light has an adverse effect, so is with too much light. There are several signs that your moon cactus is exposed to too much sunlight.

Sunburn

Sunburnt moon cactus develops brown patches of color on its epidermis. The patches look calloused and rough.

The damage of sunburn is irreversible. If you notice this sign, move your moon cactus right away to a shade where it gets indirect exposure.

Discoloration

Moon cactus getting too much sun will change its color. From being vibrant and happy, it will start to look bleached and dull. The intense light from the sun causes the pigment to change.

Sometimes the moon cactus rootstock will turn yellow or brown. But take note that this sign can also be associated with other reasons like disease or overwater. So, use a wise judgment when assessing issues of your plant.

Wrinkled/Shriveled

Prolonged exposure to sunlight will cause the moon cactus to get wrinkly from the outside. Often a result of being scorched.

The water in the plant’s tissues was all dried up because of the intense heat from the sun. The plant, mostly the upper portion, will appear shriveled, and there’s little we can do to a shriveled moon cactus.

Takeaways

  1. Moon cactus prefers a spot where it can receive 2 hours of filtered morning or afternoon sun and another 4 hours of bright light for the rest of the day.
  2. A south-facing or an east-facing window will make a moon cactus happy since it can get enough light in this position.
  3. It is imperative to know the light requirements of your moon cactus because little or too much can have an adverse effect on the plant. Giving your moon cactus the right amount of sunlight every day will lengthen its life span.

Sources

“Lighting Indoor Houseplants,” David H. Trinklein, University of Missouri Extension

“Etiolation,” Writing in Biology, University of Massachusetts Biology Department

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Esther

Esther is the self-proclaimed cactusholic :D of the team. She owns a cacti shop with hundreds of plants that she takes care of. Esther has many years of experience in growing and caring for drought-resistant plants like cacti and succulents.

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