Cultivation of tomato seedlings in the winter-spring period takes quite a lot (70-90 days), causing high costs of heating, and production. By selecting the appropriate date of sowing and applying a growth improver the period of breeding can be shortened. The goal of this study was to determine the effect of selected growth enhancers on growth of tomato seedlings in four different sowing dates, compared to untreated seedlings. The study was conducted in a heated greenhouse of the Vegetable Crops Department at the Faculty of Agriculture, University of Zagreb. The seeds of a tomato cv. 'Rutgers' were sown in polystyrene containers with 104 pots on four sowing dates (26 February, 9, 19 and 30 March 2015). Immediately after pricking and twice more in between of 10-12 days seedlings were treated with foliar growth enhancers Bio-Plantella super F and Ekorast, in concentration of 0.15%. During each treatment, morphometric observations regarding the seedlings’ height and number of leaves were performed. After completion of the cultivation of seedlings, the mass of underground and above-ground part of the plant as well as the content of dry matter in the plant parts were determined. The effect of applied bio-stimulant varied depending on the planting date and the observed characteristics. In some cases the positive effect was absent, so the maximum values were therefore determined in untreated seedlings or, on the other hand, it showed to be no significant difference regarding the treatment and control. Besides biostimulant, the growth and the development of seedlings is affected by the microclimate conditions of the greenhouse, which becomes noticable in the duration of the production cycle. Growing of the seedlings lasted for 42 days for the sowing date of 30 March and, in comparison, 55 days for the sowing date of 26 February. In accordance to the time needed for growing seedlings and the positive affect of biostimulants, the sowing date of 30 March can be recommended, combined with three treatments of a biostimulant Bio-Plantella super F (at a concentration of 0.15 %) over a period from pricking to planting.