To my knowledge, none of the cacti around north-central Texas or central Oklahoma are legally endangered or threatened, but cacti can be highly desirable to plant collectors. So, PLEASE PLEASE PLEASE make sure any cactus seeds you have acquired are from a sustainable and legal source! The three species I have grown (below) are relatively common.
When I have encountered cactus genera in articles and resources, it appears the species in the genera Coryphantha, Escobaria, and Mammillaria seem to get reassigned among each other periodically, so I’m going to guess that similar conditions apply to all. I will specify the species given if it’s one of the three I have grown that are common in our region.
Perhaps a pinch of local dirt from near the same species of adult cactus to ensure they get suitable mycorrhizal partners (Carillo-Garcia et al. 1999; Harding 2017). Most sources I read about did not talk about this aspect of germination, so I imagine many can make it without it, but germination or survival may not be as good. I didn’t do this, but if I try again in the future I will see if it’s possible.
They may need a bit of richer soil, as might be found under a nurse plant such as a tree or shrub or neighbor plant (Carillo-Garcia et al. 1999; Muro-Pérez et al. 2014). However, not too rich, as more northern Coryphantha (like ours presumably) prefer less organic matter. But not much. No details are given on how much is too much. Think about where you find the little round cacti around here normally – it’s usually up on barrens or dry hilltops, not a lush forest humus layer.
Make the seeds’ environment humid.Page 3 of Newland et al. 1981 provides a recommended cactus sprouting soil recipe and humidity-containing bag. As it’s for Arizona, I imagine it would work just as well for our cacti farther east here (ie if Arizona cacti can take the humidity recommended, ours probably need at least that). Edit summer 2022: we used plastic trays with clear lids to keep things humid for the 2022 Montana C. sulcata and got great germination rates (32+ out of around 50 seeds).
How to get them to sprout
Germination rates vary and fresher (ideally this season’s) seeds seem to be better. Love and Akins (“Second summary of the native seed germination studies of Norman C Deno: species with names beginning with letters C through E“, 2019, Native Plant Journal, vol. 20, issue 1, pp 65-97; not freely available online, so you’ll need to get it via interlibrary loan from your local library if you want it), actually have results for E. vivipara (22% germination in 1-4 weeks, at 70°F. with “a few more” seeds sprouting the following year) and E. missouriensis (65-80% in 1-6 weeks, specifically noted as being from freshly collected seeds, temperature not specified). For one Mammillaria species, less than a year old is best and two years was the maximum but germination was lower (Flores-Martínez et al. 2008). Another source said 2-3 years old at most, but I could only read the abstract as the rest of the article was in Russian. I would err on the side of planting sooner rather than later. My 2019-collected Coryphantha sulcata seeds (ie two years old) only had one germinate in 2021 and it took from Sept. 28 to mid December.
Surface sow. Most species, and this probably includes our local species (the three above at least) need light (pp 426-427, Barrios et al. 2020), so put them on the surface of the soil. Muro-Pérez et al. (2014) also argue against burying for a different species of Coryphantha.
Most cacti do well around 20-35 degrees C (aka room temperature or warmish), with an optimum of around 30 C (Figure 4, Barrios et al. 2020), including for temperate zone cacti (which is where we live).
I’m waiting to get this article via interlibrary loan and will update the post if it has anything new: R. BREGMAN, F. BOUMAN, Seed germination in Cactaceae, Botanical Journal of the Linnean Society, Volume 86, Issue 4, June 1983, Pages 357–374.
For the babies, semi-shaded is apparently better as they would normally be sprouting between rocks or under some sort of “nurse plant” that has kinder microclimate than the seedling just baking on its own in the harsh world. This factoid was for Mammillaria, but it seems reasonable for its cousins. Edit (summer 2022): We observed sunscald on baby Coryphantha sulcata (Montana genotype) in the plant window (which only gets morning sun, but that’s a lot even in summer I guess) and a single coffee filter over each appeared to solve that problem within a week.
Coryphantha as a genus is considered “easy” to grow, but it says the species from the US are usually more difficult to grow (yay us…) than ones from farther south. The link in the previous sentence says that you should ensure good drainage in permanent planting (such as bigger rocks in the bottom of the pot, never letting water stand, and not watering in the winter). Apparently clay containers let the plant get too cold in winter, though I wonder if that matters for our native ones. But, things in pots do get colder than things in the ground, so consider if you can find a plastic one instead like that source recommends. Just by accident my cacti are in a plastic container.
A lot of seedlings may die. Riley and Riley (2018) were studying an endangered cactus and they had 4 of 20 seedlings survive after three years, so maybe my just having a few surviving for our local common species is not bad??