The tallest structures on the surface of Earth are trees, which can reach 120-130m already. But I want something much bigger. In the setting of my magic-powered sci-fi story, humans use bioengineered creatures to build organic skyscrapers: the Spires.
Initially, Spires comes as human-sized 'seeds' which, one planted in an appropriate ground, are supplied by pumps with a steady flow of nutrients. The Spires have no branches or leaves, it is mostly a vertical pole supported by strong roots. Spires have multiple hearts to propel the flow of nutrients up to the latest stages, hence overcoming the limitation of our IRL trees.
After its colossal growth over a decade, the Spire is emptied out and human habitations installed within.
Geometry of the Spire would be like a thin cone with its base on the ground. The habitable section is considered as any portion with a width larger than 3 meters. I would like the diameter of Spire's base to be between 50-100 meters.
What organic materials would be strong enough to support the growth of the habitable section of such a structure up to a kilometer?
Answers involving really organic materials/structures, such as wood or mother-of-pearl, would be preferred over the ones with yet-artificial compounds such as carbone nanotubes or graphene.