We demonstrated the isothermal growth of DNA nanotubes at room temperature using a Mg-free monovalent NaCl containing buffer (TANa) without the need of an annealing step. Starting from a mixture of 5 different DNA strands, nanotubes with the desired structure grow for days as verified through different microscopic techniques such as TEM, cryo-electron microscopy and fluorescence microscopy. Frequency and length fraction analysis show the gradual disappearance of smaller nanotubes and appearance of longer nanotubes over time, likely because joining events are more favorable when compared to the case of assembly using divalent cations that favor kinetic trapping. This results in a sustained growth over days allowing a simple molecular program of a few elementary self-assembling bricks to reach mesoscopic dimensions (1 -100 µm) while ensuring near flawless assembly at the nanoscale level. This characteristic constitutes a promising asset for the design of future self-assembled smart materials capable of adaptation and self-healing.