Growing Strangler Figs in Coconuts. Ideation of Carbon-Negative, Living Infrastructure

Carbon-negative, Living Infrastructure has the potential to generate revenue, draw down atmospheric carbon and benefit both human health and biodiversity whilst cooling cities and strengthening urban climate resilience. Living Root Bridges (LRBs) are the most well-known examples of living infrastructure. LRBs are functional pedestrian bridges formed from the living aerial roots of Strangler fig trees (Ficus subgen. Urostigma). Unfortunately, the 50–100 year gestation period required to ‘grow’ a LRB installation renders their integration into urban spaces untenable. However, it may be possible to significantly reduce LRB construction times if conditions favourable to inter-specific anastomosis are provided. A significant challenge is to first identify a growth media capable of providing moisture and nutrients whilst Strangler figs are suspended supra-situ. Whole coconuts are readily available across the tropics. Coir fibres extracted from the mesocarp of coconut husks have proven to be a suitable growth media for containerised plant production. However, no previous studies have investigated the potential of using whole, unhusked coconuts as plant growth containers. This study investigates the potential for whole coconuts to be used as growth containment units for a common Strangler fig, Ficus benjamina. Strangler fig cuttings were grown in five whole-coconut treatments; high-quality potting mix, coarse sand, retted coconuts, perforated and unperforated coconuts. No significant between-treatment difference was observed in the three parameters studied, diametric growth, leaf count and mass accumulation. Whole, untreated coconuts are a suitable medium for the production of Strangler figs. The widespread availability of whole coconuts makes them an ideal growth containment option for accelerated construction of ultra-low-cost, carbon-negative, living infrastructure. The integration of carbon-negative, self-repairing Living Infrastructure into urban spaces represents a low-cost opportunity to provide climate-resilient infrastructure whilst simultaneously cooling cities and enabling greater access to green spaces. Living Infrastructure instillations in tropical urban spaces such as Cairns or Singapore may also have the potential to become popular tourism attractions.