Grow moon cactus in bright light, not hot midday sun. Moon cactus is a colorful Gymnocalycium mihanovichii top grafted onto a green stock. The top cannot live on its own roots.
Give the colorful top bright light, not hot midday sun
| Factor | Recommended | Avoid |
|---|---|---|
| Light | Bright light. A sheer curtain on a south window, or an east window | Do not sit the colorful top in hot, unshaded midday sun |
| Mix | Cactus mix with grit, in a pot with a hole | Do not keep the green stock in peat that stays wet |
| Water | Soak when the mix is dry in spring through fall | Do not pour water into the graft line or leave the saucer full |
| Winter | Almost dry. Bring the pot in before about 50 F | Do not keep a warm, wet pot all winter |
| Graft | The colorful top stays on a living green stock | Do not treat the colored ball as a cactus that can root alone |
The colorful top has little or no green tissue, so it cannot make its own food. A green column under it — often a dragon-fruit cactus — feeds the top. Give the plant bright light, but keep hot midday off the colored ball so it does not bleach or scorch. [1] [2] chin cactus on its own roots is the green globe in this catalog — see How to Grow Chin Cactus.
- Place it in bright light. An east window, or a south window with a sheer curtain, is the usual home spot.
- Use cactus mix with grit. Ordinary potting soil holds water against the stock.
- Soak until water runs out, then wait until the mix is dry. Empty the saucer. Keep water off the graft line.
- In winter, keep the pot almost dry. Bring it in before about 50 F. Cold can kill the colorful top while the green stock still looks alive.
Does moon cactus need full sun?
Give it bright light, not hot midday on the colorful top. A scorched top fades and then collapses.
How often should I water moon cactus?
Soak when the mix is dry in spring through fall, then empty the saucer. In winter, keep it almost dry.
Pot it in a draining pot, and bring it in before a chill
Moon cactus is a pot plant. Use a small terracotta pot with a hole, about the same size as the nursery pot, so the mix dries. After you pot it, wait about a week before the first soak. [3]
- Use a pot with a hole and cactus mix. Do not put a layer of gravel in the bottom.
- Choose a pot only a little wider than the roots. A wide dish of wet mix rots the stock.
- Set the plant at the same depth it grew. Do not bury the graft line.
- Wait about a week, then soak once, and wait until the mix is dry again.
- Bring the pot in before about 50 F. If the green stock makes side shoots, cut those off so they do not steal food from the top.
Can I grow moon cactus in a pot?
Yes. Use a small pot with a drainage hole and cactus mix. Bring it in before about 50 F.
If the graft fails, set the top on a new green stock
The colorful top and the green stock grow at different speeds, so the union often fails after a few years. You cannot root a fully colored top in mix — it starves. If the stock turns soft, or the top leans off, cut a fresh green column and set the top back on.
- Wear gloves. Use a clean, sharp knife. Cut the colorful top off with a flat face.
- Cut the top off a rooted green column of about the same diameter, such as a young dragon-fruit cactus.
- Set the colorful face onto the green face so as much of the rings overlap as you can. Hold the pair with a rubber band from the top to the pot.
- Keep it in bright light, out of hot midday, until the join feels firm. Then water as usual when the mix is dry.
How do I save a failing graft?
Cut the colorful top off, set it on a fresh green column of about the same width, and hold it with a rubber band until the join firms. Do not try to root a fully colored top in mix.
Not a green chin cactus — and not a Christmas cactus
Moon cactus is not a green chin cactus on its own roots. dwarf chin cactus and a green chin cactus grow without a graft — see How to Grow Chin Cactus. [4] A Christmas cactus is flattened pads, not a colored ball on a column. See How to Grow Christmas Cactus. The green stock is often a dragon-fruit cactus, but this pot is not a fruit crop — see How to Grow Dragon Fruit only if you are growing that plant for fruit.
Is moon cactus a Christmas cactus?
No. Moon cactus is a colorful globe grafted onto a green column. Christmas cactus has flattened pads and a different watering rhythm.
If the colorful top leans or the stock goes soft, cut a fresh green column and set the top back on.
FAQ
How long does a moon cactus live?
Often only a few years, because the top and the stock grow at different speeds. You can keep the color by setting the top on a new green stock.
Do I fertilize moon cactus?
You do not have to. If you feed, use a weak cactus fertilizer in spring and summer only. Skip winter.
Can I root the colorful top in mix?
No. A fully colored top has no green tissue to feed itself. Graft it onto a living green column.
Is ruby ball cactus the same plant?
Yes. Ruby ball, Hibotan, and moon cactus are shop names for the same grafted Gymnocalycium top.
Related guides
Recommended plants
References
- [1] NC State Extension Gardener Plant Toolbox -
https://plants.ces.ncsu.edu/plants/gymnocalycium-mihanovichii/ - [2] Almanac.com -
https://www.almanac.com/plant/moon-cactus-care-tips-growing-vibrant-cactus-plants - [3] Iowa State University Extension -
https://yardandgarden.extension.iastate.edu/how-to/growing-succulents-indoors - [4] Encyclopaedia Britannica -
https://www.britannica.com/plant/chin-cactus
This note is part of Gymnocalycium Guides.
More first-season notes by plant are gathered in How to Grow Guides.
Updated: Reviewed by Bosquelle Editors