Since I can’t stress the importance of sterilization enough when talking about sowing succulent seeds… I will say that I’ve toyed with different methods of sterilizing the seeds (and the husks) themselves. I used to use a diluted bleach solution, but I was afraid that might be too effective and decrease germination rates. I’ve started using, instead, a diluted peroxide solution, which some university studies have shown can increase germination rates and vigor.
After talking about it in a succulent seeders group, I decided I had enough seeds from my home-grown hybrid to run a controlled experiment; same batch of seeds, same age, same tray, but three groups: one with a pre-soak in tap water, one with a pre-soak in diluted peroxide, and one with no pre-soak.
The biggest difference seems to be in performing a presoak of any kind. Both of the presoaked varieties showed speedier times to germination, and initial vigor in the first few weeks was noticeable. Over time this early jump start has given these groups quite a boost. There’s an advantage to the peroxide solution, but it’s a smaller margin compared to plain tap water (a few days) and overall, the germination rates stayed pretty even – but this may be because my self-harvested seed was incredibly fresh, and seems to be a vigorous hybrid on its own.
However, as time has passed, an interesting nuance has developed that may indicate this jump start has a downside. The section of the tray that was presoaked for four hours in the diluted peroxide started having a problem wherein the roots grew fast and did not penetrate the soil as effectively; instead of pulling the seedlings down into the soil, they ended up pushing the plantlets up and out of the soil to the point they flopped over. Some of these plantlets developed secondary roots that then anchored them, sideways, where they fell; as the original roots grew, they pushed out from the plantlet and against the soil, arcing into the air. This is bad – exposed roots can dry out and die; plantlets in direct contact with damp soil increases the odds of fungus problems or rot. You’ll see in this picture numerous plants with exposed roots, laying on their side.
Some of the roots were too long to simply prop the plantlets up and spoon new seedling mix in to cover the exposed root.
Despite being three months old (only), I decided I needed to address this before I started losing some; with a toothpick and a gentle hand on a pair of tweezers, I extricated as many of the wayward seedlings as I could. Within the tray I either tried to create spots where I could bore a space to replant them (shoving roots down with the toothpick before nudging the soil mix to backfill the holes) or taking the ones with the most erraticly shaped roots and repotting them in a taller 2″ plastic square pot – the kind I normally use when I separate them out into individual containers around the 1 year mark, except I loaded them up four to a pot (since haworthia seedlings seem to have increased vigor the more densely they grow together).
Adding a bit more fresh mix on top and then spritzing around the fresh replants seemed to work, for now – but time will tell if they rebound from the disturbance. I’ve generally tried to wait until around the 1 year mark to prick out seedlings and repot them, but these seemed vigorous and fast growing enough I’m hoping they do fine and this ended up more help than hindrance. I’m not convinced that the fault lay in the presoak, but it seems suspicious the problem was marginally present (3/22) in the water presoaked section, and heavily present in the peroxide presoaked section (around 8/24 of seedlings).
Peroxide presoaks will likely continue to be part of my regimen, but it may necessitate adding a bit more grit on top of the seedlings once they start germination to make sure they anchor into the substrate adequately.