This study was designed to determine the chemical composition, antioxidant activity, and selected bioactive compound content and occurrence in whole immature and mature garlic plants grown from air bulbils. Two winter garlic cultivars, Harnaś and Ornak, of Polish origin, were cultivated from air bulbils at the Experimental Station of the Agricultural University in Kraków, Poland. Harvest bunching of garlic of both cultivars was carried out in May and in June. Mature plants were harvested in July. In whole plant proximate analysis, the concentration of vitamin C, total polyphenols, antioxidant activity, carotenoids, chlorophyll a and b, as well as glutathione level were determined. P-coumaric acid was found in Harnaś and Ornak samples collected in May. Sinapinic acid was identified in Ornak samples collected in June and July. Identification of sulphur compounds depended on the term of harvesting. Significantly higher content of total phenolic compounds, antioxidant activity, as well as other bioactive compounds, was measured in the Harnaś and Ornak cultivars harvested in May. A significantly lower level of bioactive compounds was determined in mature plants harvested in July. The organosulfur compound profile and polyphenolic profile depended on the time of harvesting. Immature garlic cultivated from air bulbils is recognized as a potential source of bioactive compounds in human nutrition, however, more research, in particular in vivo studies, is required to confirm its functional properties.