Two field experiments were carried out on clay soil in El-Gemmeiza Agricultural Research Station, Agricultural Research Center, El-Gharbiya Governorate, Egypt during 2013 and 2014 seasons to study the effect of five potassium treatments and four foliar applications with Zinc and Manganese on growth, earliness, yield, yield components and fiber quality of Egyptian cotton cultivar Giza 86 (Gossypium barbadense, L.). The experimental design was a split-plot with four replications. The main plots involved the five potassium treatments namely; A- Soil application of 24 kg K₂O/fed. as potassium sulfate at thinning, B- Foliar application of 5 kg potassium sulfate/fed., C- Foliar application of 2.5 g potassium citrate/L., D- Foliar application of 500 cm³ potassium humate/fed. and E- Foliar application of 2.5 cm³ potassium silicate/L. and the sub plots involved the four foliar applications of Zn and Mn namely;  1- Control (without foliar application), 2-Foliar application of Zn-EDTA, 3- Foliar application of Mn-EDTA, and 4- Foliar application of Zn-EDTA + Mn-EDTA.  The timing of foliar applications was at the start of flowering and 15 days later. The most important results obtained could be summarized as follows: 1-The potassium treatments gave significant effect on plant height at harvest, no. of internodes and sympodial/plant, no. of open bolls/plant, boll weight, seed index and seed cotton yield/plant as well as /fed. in both seasons and lint percentage in the second season only, in favor of foliar application of 2.5 cm³ potassium silicate/liter water. Also, potassium treatments gave significant effect on internode length in both seasons, in favor of foliar application of 2.5 cm³ potassium silicate/liter water. On the other hand, the potassium treatments gave insignificant effect on first sympodium node, days to first flower, upper half mean length, uniformity index, micronaire reading and fiber strength in both seasons.2- Foliar application with Zn and Mn treatments gave significant effect on plant height at harvest, no. of internodes/plant, internode length, no. of sympodia/plant, no. of open bolls/plant, boll weight, seed index and seed cotton yield/plant as well as /fed. in both seasons and on lint percentage in the second season only, where the superiority was found in favor of applying Zn and Mn in mixture at one level for each (2 g/L water) twice at the start of flowering and 15 days later. However, insignificant effect was obtained due to these treatments on first sympodium node, days to first flower, upper half mean length, uniformity index, micronaire reading and fiber strength in both seasons.3-The interaction between potassium treatments and foliar application of Zn and Mn treatments gave a significant effect on plant height at harvest, no. of internodes/plant, internode length, no. of sympodia/plant, boll weight and seed index in both seasons and no. open bolls/plant, seed cotton yield/plant as well as /fed. in the second season only, where the highest values of these traits were obtained from foliar application of 2.5 cm³ potassium silicate/liter water and foliar application with Zn and Mn in mixture contains 2 g/L water from each element twice (at the start of flowering and 15 days later). This interaction gave insignificant effect on first sympodium node, days to first flower, lint percentage, upper half mean length, uniformity index, micronaire reading and fiber strength in both seasons.