Precise control of liquid-solid interactions within sub-micrometer spaces is critical to maximize the active surface areas in porous materials, yet is challenging because of the limited liquid penetration. Here we discover an effective, dry-climate natural plant-inspired approach to guide water into sub-micrometer graphene microwells (Sub-μGWs) and to tune the transition from the hydrophobic to superhydrophilic states. Dry plasma texturing of Sub-μGWs by graphene 'nano-flaps' which adjust the tilt and density upon controlled liquid evaporation leads to controlled and stable sub-micrometer-scale surface modification and variable wettability in a wide range. This effect helps capture Au nanoparticles on the Sub-μGW surfaces as a proof-of-principle water purification platform and tune the charge-storage capacity and frequency response of Sub-μGW-based supercapacitors without altering the Sub-μGW backbones. The outcomes may be extended into diverse materials and solutions thus opening new opportunities for next-generation devices, systems and applications.