•The application of plant growth regulators (PGRs) increased the lint yield and potassium (K) uptake in field-grown cotton.•PGRs improved the partial factor productivity, agronomic efficiency and apparent recovery efficiency of K fertilizer.•PGRs increased the ratio of K in N:P:K in cotton lint.The effects of plant growth regulators (PGRs) and potassium (K) fertilizer on cotton (Gossypium hirsutum) yield have been well documented but the role of PGRs on K use efficiency is poorly understood. Our specific objective was to determine whether foliar application of PGRs could improve K use efficiency in field-grown cotton. Field experiments were conducted with or without K at two sites (Beijing and Hebei, China) varying in available soil K during 2010 and 2011, with cotton cvs. Guoxinmian3 (GX3) and SCRC28 as test materials. Foliar application of the PGRs, mepiquat chloride (MC) and Miantaijin [MTJ, a combination of MC with diethyl aminoethyl hexanoate (DA-6)] during squaring and flowering periods significantly increased the lint yield and K uptake in most situations at Beijing location and had a consistent tendency to increase lint yield across K fertilizers and years at Hebei location. The partial factor productivity (PFPK) and agronomic efficiency of K (AEK) were enhanced by the application of the PGRs in most situations in Beijing, especially in 2011 and for the cultivar GX3. Although differences in the apparent recovery efficiency of K (REK) between PGRs and control were not significant, a positive and consistent effectiveness of PGRs on REK was observed across sites, years and cultivars. Therefore, the application of PGRs would be a useful practice for improving K nutrition and lowering the cost of K fertilizer input in cotton production.