A two-factorial experiment was conducted in 2012-2014 in a greenhouse owned by the Department of Horticulture at the University of Warmia and Mazury in Olsztyn. The experiment had a randomised block design with three replicates. The first experimental factor were six botanical varieties of basil: sweet basil, Thai ‘Siam Queen’ basil, Greek ‘Minette’ basil, purple basil, lemon basil and cinnamon basil. The second experimental factor was container size and the number of plants per pot: 0.7 dm3 container with one plant per pot, 3.0 dm3 container with one plant per pot, 3.0 dm3 container with four plants per pot. In successive years of the three-year experiment, between 22 and 24 February, containers filled with organic substrate (sphagnum peat) were placed on movable tables in the greenhouse, depending on pot size (0.7 and 3.0 dm3). Once-over harvest of basil herbage was carried out between 17 April and 7 May. The plants were cut at 5 cm above the substrate surface. Total yield and marketable yield were identical because no mechanical damage to leaves or symptoms of leaf diseases were observed. The content of dry matter, total sugars and L-ascorbic acid in basil herbage was determined. Basil ecotype had a significant effect on leaf greenness index, fresh herbage yield, dry herbage yield, and on the content of dry matter and total sugars. Growing basil plants in 3.0 dm3 containers, with four plants per pot, contributed to a significant decrease in fresh and dry herbage yields, in comparison with the remaining treatments.