A controlled greenhouse experiment was undertaken during the 2021–2022 growing season in the Al-Tahiriya region, north of Babylon Governorate, Iraq (32°36′59 ′N, 44° 22′ 25′E), on loamy soils, to study the effects of foliar application of potassium (K) and nano-zinc (Zn) on vegetative & reproductive growth of tomato (Lycopersicon esculentum Mill. cv. Wejdan). The experiment was laid out in a randomised complete block design (RCBD) with three replications, consisting of four Levels of potassium sulfate K (0, 25, 50, and 75kg/ha) and four concentrations of nano zinc (0, 1, 2 and 3g/L) treatment. Foliar treatments were applied at an interval of 30 leaf days, starting 40 days after transplanting and continuing until 70 days after transplanting. Results were analysed using the Least Significant Difference test at a P ≤ 0.05 significant level. Application of potassium at 75 kg ha-1 significantly enhanced vegetative growth, viz. plant height, number of leaves per plant, leaf area, shoot dry weight, chlorophyll content, leaf nitrogen content and leaf concentrations of phosphorus and potassium. Potassium fertilisation at 75 kg ha-1 also increased flowering with an average of 16.20 inflorescences per plant and 14.05 flowers per inflorescence. Foliar application of nano-zinc at 3 g/ L increased the plant height, number of leaves, leaf area, shoot dry weight, chlorophyll content, leaf N, P and K contents, and number of inflorescences and flowers per inflorescence with averages of 215.45 cm, 50.58, 177.75 cm 2, 221.08 g, 50.93 SPAD, 1.72%, 0.56%, 1.92%, 16.15/ plant and 13.83/ inflorescence, respectively. The interaction between the combined application of 75 kg/ha of K and 3 g/L nano-Zn induced significant (P ≤ 0.001) the highest values for all vegetative and reproductive parameters measured to indicate interaction between the two nutrients, revealing the benefits of utilising potassium and nano-zinc under certain levels of foliar treatments of tomato produced under protection.