The Asteraceae family in Siberian Asia exhibits remarkable biodiversity and has long served as a valuable resource for domesticating various beneficial plants with medicinal, therapeutic, and industrial significance to humanity. In this work, we studied for the first time the chemical composition of six understudied or previously unexplored plant species, Artemisia jacutica (AJ), Carduus nutans subsp. leiophyllus (CL), Cirsium heterophyllum (CH), Echinops davuricus (ED), Ixeris chinensis subsp. versicolor (IV), and Lactuca sibirica (LS), which were successfully cultivated under open-field conditions as biennial or perennial crops. We profiled these species, employing a liquid chromatography–mass spectrometry approach, identifying over 100 phenolic compounds. Among these compounds were hydroxybenzoic acid glucosides, hydroxybenzoyl/p-coumaroyl/feruloyl quinic acids, hydroxycoumarin O-glucosides, caffeoyl/p-coumaroyl/feruloyl glucaric/tartaric acids, O- and C-glucosides of apigenin, acacetin, luteolin, chrysoeriol, 6-hydroxyluteolin, pectolinarigenin, kaempferol, quercetin, isorhamnetin, and tri-/tetra-O-p-coumaroyl spermines and spermidines. All examined species exhibited a significant accumulation of phenolic compounds throughout the experimental period, reaching levels comparable to or exceeding those found in wild samples (WSs), with the best total phenolic content for AJ at 26.68 mg/g (vs. 26.68 mg/g in WS; second year), CL at 50.23 mg/g (vs. 38.32 mg/g in WS; second year), CH at 51.14 mg/g (vs. 40.86 mg/g in WS; sixth year), ED at 86.12 mg/g (vs. 78.08 mg/g in WS; seventh year), IV at 102.49 mg/g (vs. 88.58 mg/g in WS; fourth year), and LS at 127.34 mg/g (vs. 110.64 mg/g in WS; fifth year). Notably, in the first year of cultivation, approximately 40–60% of the wild-level target compounds accumulated in the plants, with even higher levels detected in subsequent years, particularly in the second and third years. This study highlights the potential of cultivation to produce new Asteraceae plants rich in bioactive phenolics.