Lacy phacelia (Phacelia tanacetifolia Benth.) is relatively unknown and information’s about this species in our environment are limited. This species originally from America arrived in Europe in the 19th century, primarily as decorative and honey production plant. The main aim of this study was to determine the morphological characteristics of phacelia which affecting its competitive ability at two different spring sowing dates. In addition, research was made to identify other morphological characteristics to ensure unknown data for description and growing of these cultivated species. The experiment was conducted during 2015 growing season at Maksimir experimental station, Faculty of Agriculture. Measurements of 20 morphological characters were made at 20 randomly selected plants within each sowing date. Presence of weeds in both phacelia crops was visually monitored and recorded. Sowing date influenced on morphological characteristics of phacelia in this study. Phacelia plants from early spring sowing were characterized by an lower stem height, smaller diameter of the stem, smaller number of internodes and branches per stem, smaller number of leaves per plant, smaller number of inflorescence branches per plant, fewer flowers per plant and less fruit per plant) compared to plants from late spring sowing. Reasons for smaller plants from the first sowing date probably were less favorable environmental conditions (high precipitation and low temperature) during the initial period of phacelia growth and poor physical soil conditions (compacted soil) in early compared to late sowing. Early spring phacelia sowing date resulted in 26 different weed species in crop while in late spring sowing date only six species of summer weeds were recorded. Results of this study indicate on greater plants development and less weed species in phacelia crop from late compared to early spring sowing date.