Last updated on August 25th, 2023 at 12:30 pm
Mammillaria rhodantha, commonly known as the rainbow pincushion or rainbow cactus, has beautiful flowers and an interesting growth pattern that’s sure to grab attention no matter where you place it in your home or office.
The rainbow pincushion is an attractive and unusual member of the cactus family, with fuzzy yellow spines that are tipped in red, orange, or magenta. It’s frequently sold as an indoor plant, but it’s actually a species of cactus that has adapted to life outdoors in USDA zones 8-11. It grows to just two inches tall and spread up to eight inches wide, so it doesn’t need much space to thrive.
Mammillaria rhodantha is an easy cactus to grow and can add bright color to your garden or houseplants. It makes an excellent addition to any collection of succulent plants.
Origin and distribution
Mammillaria rhodantha is native to Mexico. It was first described in 1824 by Carl Sigismund Kunth. The rhodantha part of its name comes from genus Rhodanthe which has a similar form and flower colors but with different flowers and fruit.
The mammillaria part of its name comes from those star-shaped hairs on top of tubercles. Its range extends into Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, Panama and Colombia.
The natural habitat for this plant are scrublands at an altitude up to 1,000 meters above sea level. Its flowering period starts from the end of spring until the end of summer when it starts producing berries that mature during fall.
They can be found growing as solitary plants or in groups. When grouped together they give off a rainbow effect because they have so many different colors like pink, red, purple, orange and yellow.
These plants are best grown inside where they can receive indirect sunlight most of the day; direct sunlight will cause sunburned spots on the leaves.
Mammillaria rhodantha propagation
Mammillaria rhodantha are easily propagated from stem cuttings. These can be done at any time of year, but winter is best to prevent plants from getting too large in a season.
Cuttings should be pencil size or slightly larger, and approximately 6-12 inches long if potted or planted directly into well drained soil. Trim off the bottom few leaves and place the cutting in an inch of damp sand until roots form.
Once roots have formed, plant the new plant or pot it up with potting mix. Keep warm and moist until established, then keep the new plant outdoors during summer months and bring indoors before first frost date.
When watering, water thoroughly and allow top layer of soil to dry out between waterings. In addition, feed monthly with a general-purpose fertilizer diluted by half and follow label instructions for best results.
Mammillaria rhodantha care information
Mammillaria rhodantha is another excellent beginner cactus. It is probably more tolerant of neglect than other similar-sized mammillarias, and even when its roots have been allowed to dry out it will usually bounce back after a few days of being watered well.
Light requirement
Mammillaria rhodantha is among a handful of types of cacti that require absolutely no sunlight to survive and thrive. That’s right—you can keep these guys inside in your windowsill, and they’ll be happy as clams.
In fact, if you place them in direct sunlight during winter months, they may suffer from sunburn. On the other hand, during summer months it is not uncommon for people to grow mammillarias outside.
Their small size and wide availability make them an ideal houseplant for those who do not have the time or inclination to care for more complex cacti such as saguaros or giant barrel cactus plants.
Soil/potting mix
Any cactus or succulent garden soil will do for growing your Mammillaria rhodantha, but it’s important to note that all growers are different, so you may want to ask around if you’re having trouble finding a soil/potting mix specific to these types of plants.
The general rule is that potting mix should be well-draining, so it can accommodate plant roots without compromising their ability to absorb water. It also needs to provide nutrients and minerals for the plant as it grows.
There are a variety of pre-made mixes on the market, some of which come with fertilizer included in the formula.
Alternatively, feel free to use what you have available: sand and compost from your own yard mixed together in equal parts will work just fine!
Watering
Mammillaria rhodantha should be watered generously during their growing season, from spring to fall. During winter months, reduce watering and only water enough to keep them from getting shriveled and wrinkled.
Water throughly, making sure all of their soil is moistened; they’re susceptible to rot when overwatered. Once you figure out what is an adequate amount of water for your specific plants, stick with that amount so you know how much you need to water each week!
Fertilizer
Use a slow-release, granular fertilizer for cactus and succulents only if your plant is in active growth. If it’s dormant, you can use a water-soluble fertilizer. Use sparingly, you don’t want to overfeed your plants! Feed once a month during summer, every other month during winter months. Avoid fertilizing during the fall or winter when this plant becomes dormant.
Temperature
Mammillaria rhodantha requires a temperature of 60-70 degrees F. Unlike most cacti and succulents, it will not tolerate freezing temperatures, so it must be kept indoors in areas where winter temperatures drop below freezing. If you live in an area that experiences subfreezing temperatures year-round, consider keeping your pincushion outside during warmer months, then moving it inside for winter.
Humidity
Mammillaria rhodantha are native to arid and semi-arid parts of Central America. They can take a lot of heat, but will be happiest when kept in 50 to 70 percent humidity. Check your air humidity in your grow area before getting these little cacti home by placing a dry handkerchief on top of a damp cloth at room temperature for 24 hours.
Pruning
Trim back all growth tips with a sharp pair of pruning shears to remove old leaves and encourage new growth. New growth is where flowers form, so removing those old leaves will stop them from flowering. This is called pinching or pruning and must be done on a regular basis to keep your plant healthy.
The best time to do this is in the spring before the first shoots appear from the ground. Cut down any shoot that looks weak or has been damaged by frost damage, pests, disease or too much sun exposure.
When you are trimming off the top parts of the plant’s stem, it helps if you cut at an angle away from the center of the stem instead of straight across. Be careful not to cut into live tissue as it will cause permanent damage!
When to repot
Mammillaria rhodantha should be repotted in spring and fall to ensure they get just enough water. Repotting should be done every two years, so if your plant is growing too fast in its pot, it’s a good sign that it needs to be transplanted.
To repot, gently remove your pincushion from its pot and set it on a clean work surface.
Remove the old soil and replace with a mix of 50% sand or perlite, 25% peat moss, 25% orchid bark. Be sure to keep the roots moist at all times during the process by spraying them with water before replanting them back into the new potting mixture.
Dormancy/Winter rest
Mammillaria rhodantha, like most other cacti, are dormant during winter and require minimal care at that time. During dormancy make sure they receive as much light as possible without being exposed to cold drafts or direct sunlight.
A little water is fine but don’t give too much as that can promote rot. When your Mammillaria starts growing again in spring you may need to prune off old dead spines or reshape its form.
Otherwise, just wait for it to grow and enjoy! Be careful not to over-water during this time because the plant will be very sensitive due to the change in environment.
Mammillaria rhodantha flower & fragrance
The flowers of Mammillaria rhodantha are white to yellow-green, have a diameter of 1.5–2 cm and are usually born in clusters at the top of each stem. The fragrance is especially intense on warm days.
The flowering season is from June to September. In temperate regions it requires a minimum temperature of about 10°C for flowering, if night temperatures do not fall below 7°C . If kept dry during winter and given water and fertilizer in Spring, it will bloom again early next year.
Growth rate
Mammillaria rhodantha is a slow-growing cactus that’s not quite as drought-tolerant as some other cacti. It will appreciate regular watering during its growing season, but you can cut back to once every two weeks in winter.
Use a soil-based cactus mix with excellent drainage and keep it evenly moist. Fertilize monthly during growing season with 20-20-20 mixed at 1/4 strength.
Toxicity
Mammillaria rhodantha is one of a few genera in which all species are completely non-toxic to humans. These plants have no chemical defenses, and there are no reported incidents of any human poisonings.
Mammillarias do not contain nematocysts and, according to research done at Texas Tech University, they also do not produce skin irritants or other chemicals that might cause harm.
USDA hardiness zones
Mammillaria rhodantha thrives in USDA hardiness zones 8 through 11. The plant is a succulent, meaning it stores water inside its tissues. It should be watered sparingly and kept on the dry side to prevent rot.
Pests and diseases
Mammillaria rhodantha are susceptible to mealybugs, scale, and mites. They can also get sunburned from strong sunlight. Since most of these succulents originate in dry areas with low humidity, they’re prone to rot if overwatered. Watch for signs of decay and make sure your plant doesn’t sit in wet soil or have a saucer of water underneath it at all times.
