The research aimed to present the possibility of cultivating selected plants of the genus Ocimum in central-eastern Poland and to assess the chemical composition of the obtained raw material, considering the development stage of the plant. The research object consisted of six selected plants from the genus Ocimum: Ocimum basilicum, Ocimum basilicum var. purpurescens, Ocimum basilicum × citrodorum, Ocimum basilicum ‘Cinnamon’, Ocimum basilicum ‘Siam Queen’, Ocimum basilicum var. minimum ‘Minette’. The herb was harvested on the following dates: mid-June (vegetative stage), mid-July (beginning of flowering), late July/early August (full flowering), end of August (late flowering). The research showed that plants of genus Ocimum sp. can be successfully introduced to cultivation in central-eastern Poland. The yield of these plants was at a high level (average yield of fresh herb—1.15 kg m−2 and average marketable yield—0.14 kg m−2). Plants of genus Ocimum sp. accumulated the least essential oil, flavonoids, and tannins in the vegetative stage (mean: essential oil—0.86%, flavonoids—0.60%, tannins—0.41%). The highest content of all tested secondary metabolites was found in the variety O. basilicum var. minimum “Minette”. The variability of the content of the analyzed compounds depending on the growth and flowering stage of the plants under study is diversified. For this reason, the date of harvesting raw materials from these plants should be selected individually to obtain a high-quality product.