We've now been tracking planting outcomes closely enough, for long enough, to say something more useful than a general impression about what actually determines whether a young tree survives its first dry season in Donholm. This is a look at what four years of nursery and planting records actually show.
Species selection made the single biggest difference
Of every factor we've been able to isolate, species selection shows the clearest and most consistent effect on dry-season survival. Indigenous species adapted to Nairobi's rainfall patterns have consistently outperformed the small number of ornamental species we experimented with in our earliest, less selective plantings back in 2022, a gap that has held steady across every subsequent planting season rather than narrowing as our technique elsewhere has improved. This is the clearest evidence we have for the preference toward indigenous species that now shapes nearly everything our nursery produces.
Within indigenous species themselves, we've also seen meaningful variation, some perform reliably well across nearly every site we've tried them on, while others show much more site-dependent results, doing well in one location but struggling in another with seemingly similar conditions. That variation is part of why our site survey process, covered in a separate post, now scores each candidate site individually rather than assuming any given species will perform consistently everywhere.
Nursery hardening explains most of the rest
The second clearest factor is whether a seedling went through our full nursery hardening process before being transplanted, gradual exposure to fuller sun and reduced watering frequency in the weeks before planting, rather than being moved to open ground directly from partial-shade conditions. Seedlings that skipped or shortened this hardening period, generally in our earliest seasons before the nursery process was fully established, showed a noticeably higher failure rate during their first dry season than properly hardened seedlings planted at the same sites.
This finding directly shaped how strict we've become about the hardening timeline, even when demand for seedlings at an upcoming planting day creates pressure to move stock along faster than the process ideally allows. We've learned, sometimes the hard way, that rushing this step trades a short-term convenience for a meaningfully worse long-term outcome.
Mulching and post-planting watering matter, but less than we expected
Mulching and a consistent watering routine in the weeks immediately after planting both show a positive effect on survival, but a smaller one than we initially expected relative to species choice and nursery hardening. Our interpretation is that these two factors mostly determine how well a seedling copes with a genuinely difficult dry season on top of already-good fundamentals, rather than compensating for a poor species choice or an under-hardened seedling in the first place. In other words, mulching and watering help a good planting do even better, but they can't fully rescue a planting that started from a weaker position on the two bigger factors.
That's a useful, if slightly humbling, finding for our own training sessions, where we'd previously emphasised watering discipline as heavily as species choice. We now put more weight on getting species and nursery preparation right from the outset, treating aftercare as an important but secondary layer on top of those foundations.
What this means going forward
Practically, this data has sharpened our priorities: continued investment in the nursery's hardening process, more careful, site-specific species selection through our survey work, and slightly less anxiety about achieving perfect watering discipline on every single seedling, since the data suggests species and hardening carry more of the weight than we'd assumed. We'll keep updating this analysis as more planting seasons add to the dataset, and we'll share meaningful shifts here as they show up.
Households collecting seedlings from our nursery benefit from these same findings indirectly, every seedling that leaves our nursery has already been through the hardening process this data validated, whatever a household does with watering and mulching afterward builds on top of that same foundation.
Limitations of what this data can actually tell us
We want to be upfront about the limits of this analysis. Our record-keeping in the earliest seasons was considerably less rigorous than it is now, which means some of the comparisons between our first plantings and later, more careful ones aren't perfectly controlled, other factors changed at the same time as our nursery process improved, including which sites we chose and how experienced our team had become at planting technique generally. We're confident in the broad direction of these findings, species and nursery hardening matter more than aftercare alone, but we'd be overstating our certainty to claim precise, isolated percentages for each factor's individual contribution.
We're continuing to refine our record-keeping specifically to make future versions of this analysis more rigorous, tracking site conditions, species and hardening history more consistently for every planting rather than relying on the more informal records our earliest seasons left us with. As that dataset grows, we expect to be able to say something more precise, and we'll publish updated findings here as the picture becomes clearer.