Lately, I’ve been thinking about renovating the cactus collection here at the UConn teaching greenhouses. As it stands, the collection is good enough for most purposes, though it includes a fair amount of old material of unknown provenance and sometimes dubious identification. However, it would definitely benefit from some judicious thinning, and an infusion of new blood: representatives of interesting genera like Ariocarpus and Ortegocactus, or obscure and evolutionarily distinct groups like Maihuenia, would increase the collection’s botanical relevance as well as its public appeal.
The first step in any project to acquire a diverse selection of properly named cacti, on a limited budget, is to check the Mesa Garden seed catalog, which is truly one of the seven wonders of the modern horticultural world. If it’s a cactus that’s in cultivation, Mesa probably offers seeds, for a dollar or so per packet, and from your choice of half a dozen different collection localities. Their only weak point is a paucity of tropical cacti like Rhipsalis, which do not appreciate the high altitude desert conditions in Belen, New Mexico, where Mesa Garden is based. Well, the catalog is pretty bare bones, too, with no photographs, and descriptions that are usually around four words long. But that’s why we have illustrated books.
So, back in January, I ordered up about 40 packets of seed from Mesa. I planted a few temperate species right away, and kept the pots refrigerated to simulate winter (a process called stratification). These pots moved out into the greenhouse in March, when I also planted the remainder of the seeds (from all of the plants that do not need stratification). Spring is the best time of year to start cactus seed: longer days and warmer temperatures encourage growth. Everything was planted in a very loose mix, of 1part peat, 1 part perlite, 1 part sand and 1 part grit, and just barely covered with a bit of course sand.
Cactus seed needs moist conditions to germinate, so I kept the pots well watered. Results have been excellent so far, with hundreds of tiny plants cropping up. Different groups of cacti have different seedling types. Some have two leafy cotyledons (seed leaves), and look a lot like tomato seedlings, at least until spines appear. Others are just minute spherical blobs, from the top of which spines start to poke after a few weeks.
Now that the plants are up, I’ve been cutting back on watering, and allowing the soil surface to dry slightly. It’s definitely not a good idea to let things dry out too much at an early stage, though: even cacti are quite vulnerable to desiccation for their first season. This summer, I’ll keep the seed pots warm, on the moist side, and provide dilute fertilizer every few weeks, in hopes of getting decent sized plants established by the time growth slows down in the fall.
As expected, there have been a couple of sowings that have yet to do anything. The Opuntia (prickly pear) allies—which have relatively large, tough seeds that are notoriously slow to sprout—have been especially recalcitrant. I’ll hang onto those pots for at least another year, and may try a second cold treatment next winter.