The growth stimulation of gram plants (Cicer arietinum) by water dispersible carbon nanostructures (CNSs) is found to be dependent on the latter's morphology. The <10 nm diameter coiled single-walled carbon nanotubes (SWCNTs) are observed to be better promoters of plant growth than the ∼180 nm straight open-ended multi-walled CNTs post 7 days. In comparison, the 150–200 nm thick close-ended functionalized (CNW1) and annealed (CNW1A) carbon nanowhiskers show lesser growth stimulation. ∼570 nm CNW2 and ∼4.5 nm carbon dots (C-dots) show inferior performance. The varying growth rates suggest a hypothesis that although C-dots and SWCNT can adapt the symplastic pathway to reach the root's interior, all the CNSs are expected to prefer the apoplastic route and consequently widen the cell membrane pores due to their high potential gradient. 1D hollow nanostructures with the smallest diameters are found to be the best growth stimulators.