Context Water deficit is a limiting factor in cowpea (Vigna unguiculata) performance. Humic and fulvic acids are organic fertilisers that increase plant productivity and appear as a viable alternative to improve cowpea productivity under water deficit. Aim We evaluated the efficiency of humic and fulvic acid on the morphophysiological and biochemical properties of cowpea subjected to water deficit. Methods The experiment was conducted in a greenhouse. A completely randomised design was adopted in a 5 × 2 factorial scheme with four replications, with five doses of humic and fulvic acid, 0, 4, 8, 12 and 16 mL/L applied to plants irrigated at 100% and 25% of field capacity. Stomatal conductance (gs), water potential (Pw), plant height (H), stem diameter (SD), number of leaves (NL), number of root nodules (NR), fresh and dry weight of the aerial (FMA and DMA) and root (FMR and DMR), total soluble proteins (SP) and total phenolic compounds (PC). Key results Doses of 8 and 12 mL/L increased gs (100–200 mmol m2 s−1), reduced Pw (−0.9 MPa) and NR, increased FMR and DMR (20 and 10 g), SP (8–9 g) in stressed and non-stressed individuals. Conclusions Intermediate doses of humic and fulvic acid (12 mL/L) are recommended for cowpea production in dry regions. Implications Humic and fulvic acid together are viable alternatives for optimising agricultural production and decision making in semi-arid regions.