Care Diary: How to Grow Discocactus chrystillophilum

discocactus chrystillophilus bloom

Written byJen Greene

Animal lover, plant enthusiast, and addicted to the sunshine and warmth in San Diego.

October 7, 2021

I have held off on blogging about the care of this particular species of cactus as I’ve read and heard that they can be finicky, difficult, and tend to be quite sensitive.

I’ve had my Discocactus chrystallophilus for almost a year now, and they’re relatively small, attractive little cacti that have been a pleasure to grow and maintain in that time. Notably, however, I’ve had them exclusively in a sheltered plastic greenhouse or more recently, in my newly erected larger greenhouse.

Discocactus crystallophilus habitat and morphology

This particular species is described in Llifle as being a geographical/morphological form of Discocactus placentiformis. This form is found in Brazil, in Minas Gerais, at about 2300 feet above sea level, in rocky soil and often shares its growing area with bromeliads. 

The bromeliads are a hint to the moisture level and aeration that the roots require. It’s an unusual cactus that thrives in the same conditions as a plant typically considered quite tropical! 

They get between 3 and 4 inches tall, with an extra inch possible if you count their little cephalium. 

A cephalium is a flower-bearing, wooly, and densely bristled outgrowth at the apex of a cactus stem of certain species. It is where flowers and cactus fruit appear in cephalium-bearing species. 

Compared to a melocactus, the cephalium on a Discocactus is fairly small and nondescript. It’s white, bristled, and faintly fluffy, without the clear towering red hat that many of us are used to seeing in cephalium bearing species. 

Their bodies are green, ranging from dark to light, and potentially blushing a reddish to purple shade in bright light. Spines form in small clumps on white areoles, between 3 and 5 per areole, sometimes as many as 7. The lowest spine is usually longest, and points straight down. 

One of the most striking and exciting things about Discocactus crystallophilus is the blooming habit: once the cephalium has developed, the cactus is mature and will begin producing blooms! Mature plants bloom throughout summer with large, extremely fragrant nocturnal flowers. 

discocactus chrystallophilus
Discocactus chrystillophilus

Growth & Care Needs

I acquired my two Discocactus late in 2020, and they looked as you can see above. They were in 5″ pots, from a wholesaler who I know pots with a generous mix of pumice and cactus soil, so they were set for a while.

What I had read about their care implied that they needed somewhat consistent water, and to be protected from temperature extremes. Picking them up near the end of the year meant I was immediately throwing them into the riskiest time of year for our area: winter!

Temperature preferences for Discocactus chrystallophilus: You should keep these above freezing at a bare minimum, and they greatly prefer being much warmer than that. Recommendations online say to keep them above 60F; mine routinely experienced lows in the 30s during the coldest time of winter. I kept them on the dry side if I knew cold weather was coming, and would lightly water them if we had a warmer day (70s+).

Using even a plastic greenhouse is likely what made a significant difference in my experience growing these during periods that were definitely too cold for common internet recommendations. My little cheap greenhouse allowed them to get up to the 80s on sunny winter days, with occasional days in the 90s! At night, the greenhouse plus location (close to the house, sheltered from actually hitting freezing) kept them just warm enough to not suffer.

In summer, they do absolutely fine with extreme highs: temperatures of 110F+ in my greenhouse didn’t even phase them. I did make sure they had time to acclimate to the conditions in the new greenhouse – which was about a week or so in more shaded conditions, provided with plentiful water in the evenings. 

Discocactus placentiformis
Discocactus placentiformis

Watering, Light, and Soil 

Water, light, and soil are all tightly intertwined and really can’t be spoken of independently. In the photos above, the two Discocactus have come through the coldest winter temperatures and are showing signs of new growth in early spring (April 2021). The cactus at right had more exposure to light and cold, and blushed a purplish shade. 

With Discocactus, it seems that their roots are relatively delicate, and they are not fans of being repotted. As a result, I didn’t repot mine for nearly all of the initial time I had them (also why I haven’t blogged about their care – does it count if I didn’t repot in my own soil?). 

When it’s warm and they have plenty of light, they’ll take a regular amount of water. In colder months, I’d water them once every week or two if daytime highs in their greenhouse averaged over 75F. The main reason for this was related to nighttime temperatures – they needed to be kept from getting too dry, but they also couldn’t be too wet. In winter, I tried to water lightly: the water barely flowed out of the bottom of the pot or didn’t flow out at all. 

Once the weather warmed up, those bets were off. All through spring and into summer, I would water every few days, usually checking if it was needed by picking up their pots to look underneath or feel the weight. If the pot felt light or it looked dry underneath, I’d water the cacti thoroughly. In warmer months, I made sure to saturate the soil and see water streaming out of the drainage holes below. 

In regards to light, these should be kept in bright but relatively indirect light, at least for my area. Nearly full sun most of the day is acceptable, but they should have shade for the brightest and hottest parts of the day, typically noon to 3 pm. 

When it comes to soil, I paid attention to the blend that they thrived in before finally repotting one this summer: extremely coarse, well draining soil that was maybe 50% organic matter at most.

My eventual mix when I did repot the cacti was 50% smaller grain pumice, 40% cactus and succulent soil, and 10% decomposed granite/sand. 

The mix I found when I repotted the larger of the two was roughly 50% large-ish pumice. These larger pumice rocks are extremely nice in your soil, and the cactus roots really seem to appreciate growing around the air pockets and soil with them. As a result, on the surface, the cactus looks planted in a 5″ pot – but the roots, when you remove the pumice, are barely of a size to fit a 3″ pot. 

This discrepency doesn’t mean you should remove all the airy soil components and pot the cactus in a much smaller pot, but rather points to a very important aspect of growing the species: the roots like room to breathe. 

Discocactus bloom

The thing about Discocactus that completely entranced me was the flowers. The first time I saw them emerge, I was blown away by how quickly they emerged, and then the smell, and then how quickly they faded. 

Discocactus chrystillophilus flower will, quite literally, go from a barely visible bud to a full flower over the course of a day. They open up when the sun goes down, and slowly fade when it comes back up. I did a photo series over on Instagram of one emerging in the greenhouse on a day I was able to check it frequently. Most often, I discover a bud in the morning, see it growing once or twice during the day if I’m home, and by evening, it’s open! 

They are extremely fragrant, something that was passably noticeable when they were in the plastic greenhouse (which was small and left open at night for airflow during summer), but as strong and distinct as a woman’s perfume in the enclosed wood frame greenhouse. 

discocactus chrystillophilus bloom
discocactus chrystillophilus bloom

Honestly, I can’t get enough of the blooms. I get excited every time I see them coming. 

They will bloom all through summer and, as I’ve experienced, well into fall if their daytime temperatures remain high. In the wood-frame greenhouse, daytime temperatures are still averaging in the 100F range, which sems to be fooling them into thinking it’s still summer even as the days get quite a bit shorter. 

Fertilization doesn’t seem to heavily impact blooming; I didn’t notice a correlation between using my dilute cactus fertilizer and increased bloom frequency. Sign of appropriate fertilization or inadequate quantities? Time will tell. 

Repotting your Discocactus

I repotted one of my two Discocactus in July, not long after moving them to the greenhouse, and offer my single experience to help you if you are also repotting yours for the first time. 

Know ahead of time that they are supposed to have delicate roots. Gently use your fingers to dislodge soil, and a gentle water stream from the hose to rinse the roots if you need to. 

Gentle in this case means using the meat of your fingertips to dislodge soil, not your nails, and to avoid using a metal tool to untangle or clean off the roots. You don’t have to gingerly pat each root, but you should be gentler than you would be for, say, an opuntia or ferocactus. I did not rinse the roots of my plant, just dislodged the soil with my fingers as described. 

Follow bonsai practices for planting back in the pot. Carefully position your cactus, and place a layer of soil mixture at the bottom that is just high enough for the lowest roots to touch when you hold the cactus at the level you want it to rest at. 

From there, add soil layer by layer, jostling the cactus and using your finger or a mini rake to ensure the roots settle into the soil thoroughly. Once you’ve filled the pot, add your top dressing and then let the cactus sit, dry, for at least a week before you water it. This allows any damage in the roots to heal or callous over before you add moisture and the potential for rot to the soil. 

discocactus chrystillophilum

Discocactus chrystillophilum is a fun, cute little cactus that stays small and attractive for its entire life. The cephalium is cute and funky, the blooms gorgeous, and if you can keep them adequately warm and sheltered in winter…mature specimens aren’t inordinately difficult to grow. 

You can follow along with my cacti and other plants on Instagram! I recently attempted pollinating blooms on my two Discocactus, so be sure to follow me for news on if I’ve succeeded. 

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