The purpose of the experiment was to assess the effect of application of zinc ammonium acetate (ZAA) on yielding, morphological features and on selected vegetation indices of timothy cv. ‘Owacja’ cultivated for seeds. Zinc ammonium acetate that has a biostimulatory effect was used foliar in the carried out experiment. The experiment was conducted in the years 2015-2017 at the experimental station in Prusy near Krakow, a part of the Experimental Station of the Institute of Crop Production of the University of Agriculture in Krakow. The field experiment was set up in a randomized block design, in four replications, and the area of experimental plots was 10 m2. Degraded Chernozem formed from loess (classified to the first class quality soil) was present on the experimental area. The experiment consisted in applying ZAA as spray at three doses: 0.214, 0.267 and 0.400 kg(ZnNH4(CH3CO2)3)/ha. Based on the obtained preliminary results, it was found that application of foliar activator in a higher dose (0.400 kg/ha) caused a significant (p ≤ 0.05) increase in seed yield, 1000-seed weight and in germination capacity in relation to the control. Improvement in morphological properties was also observed. Leaf greenness index (SPAD) was also determined. Its highest value was found in plants from the treatment where the highest dose of the zinc ammonium acetate was applied. Seeds obtained from plants treated with ZAA were riper (ripeness was measured with 1000-seed weight) and had higher germination capacity in relation to control treatments.