It would be easy to fill Donholm's green corridors with fast-growing ornamental species that look impressive within a year or two. We deliberately don't, and given how often the question comes up at planting days, it's worth explaining why in more detail.
Lower maintenance, better long-term survival
Indigenous trees are adapted to Nairobi's rainfall patterns and soils, meaning they typically need less watering and intervention once established, an important consideration for a volunteer-run planting programme without a large maintenance budget or paid grounds staff to follow up on watering schedules. Many also support local birds, insects and small wildlife in ways introduced ornamentals rarely do, restoring a small piece of the ecological function the area has lost as green cover has shrunk over the decades.
Our own nursery data backs this up fairly directly: indigenous species we've hardened and planted through the nursery show meaningfully better one-year survival rates than the handful of ornamental seedlings we experimented with in our earliest, less selective planting seasons back in 2022.
The infrastructure problem with some ornamentals
Some ornamental species, additionally, have deep or aggressive root systems that damage nearby structures and drainage infrastructure as they mature, a real problem in a built-up area like Donholm where compounds sit close together and drainage lines run close to the surface. We've seen cases elsewhere in Nairobi where a fast-growing ornamental, planted without much thought to what sat underground nearby, ended up cracking a boundary wall or lifting a section of paving within a few years.
Indigenous species are, on balance, the better long-term investment for a neighbourhood this dense, even if they take a little longer to visibly fill out. It's a trade-off we're comfortable making, and one we explain to every household that collects seedlings from our nursery so the choice is an informed one.