Intro: The popular moon cactus plant is a small grafted cactus. Grafting, which can be done with many plants, is a propagation technique in which a gardener will take two separate plant species, cut them and grow them together as one plant. The plants, if they are compatible, will bond and grow as one. The top cactus of the moon cactus has a mutation that causes it to lack the chlorophyll that makes the cactus green. This mutation exposes the red, orange or yellow color beneath. Cactus that lack chlorophyll cannot live on their own – they die as seedlings unless grafted onto another cactus with chlorophyll.
Scientific Name: The two cactus species most commonly used for moon cactus are Gymnocalycium mihanovichii as the top cactus and Hylocereus spp. as the base.
Plant Type: Grafted cactus
Light: The moon cactus plant requires bright indirect sunlight. Full sun will actually harm this container plant, so keep it out of direct sunlight for long periods of time.
Water: Water moon cactus thoroughly, then let the plant dry out between waterings.
Fertilizer: You don't need to regularly fertilize your moon cactus plant, but you should dose it with a cactus fertilizer every month during its growing season (April to September).
Temperature: The tiny moon cactus won't do well in very cold temperatures, so bring it inside to overwinter during the cold winter months.
Pests and Diseases: Insect pests and diseases won't be much of a problem with the moon cactus, but you may see some spider mites or mealybugs attacking your cactus plant. The biggest problem with this plant is overwatering, which can lead to root rot.
Propagation: Grafting cactus can be difficult, so leave propagation to the grafters! It is easiest to buy a moon cactus specimen from your local garden shop, but if you can find a healthy specimen of Gymnocalycium mihanovichii that lacks chlorophyll and a healthy Hylocereus, you may want to give it a try. Follow the seven steps to grafting cactus.
7 Steps to Grafting Cactus
1. Purchase a healthy red, yellow or orange Gymnocalycium mihanovichii and a healthy Hylocereus large enough for grafting.
2. Disinfect a sharp knife (to reduce risk of infection in the cacti).
3. With the knife, cut the top off of a healthy Hylocereus. Cut a piece that is the same size of the G. mihanovichii that will be grafted onto it.
4. Trim the edges of the Hylocereus so that its edges slope downward.
5. Cut off another thin layer from the top of the Hylocereus and cut a thin layer off of the bottom of the the G. mihanovichii. Place the two cacti together so that the rings of their vascular bundles directly face one another. The vascular bundle is that small round ring in the center of a cactus’s cross-section. The vascular bundle is visible in the photo on the right.
6. Hold the two cacti together with rubber bands (don’t make the rubber bands too tight or too loose).
7. Wait two to three weeks for the two plants to grow together, and then gently remove the rubber bands.
In this video, University of Nevada Cooperative Extension's ML Robinson demonstrates how easy it is to graft cactus.
Misc. Info: Keep moon cactus in temperatures above 60 degrees, and fertilize monthly during their growing season. Moon cactus can only live for a few years.