Studies carried out in 2003–2005 included determinations of free phenolic acids content in edible parts (shoots, pseudostem) of onion, shallot, and Welsh onion grown for green bunching in the field and forced in the greenhouse. Plants for phenolic acids contents analyses were achieved from setting the small bulbs (common onion, shallot) or annual plants from the seedling setting in the case of Welsh onion. In the field cultivation, plants were grown under short-term covers made of perforated PE film and non-woven PP, while forcing was realized in heated and unheated greenhouse. Free phenolic acids contents were determined after plant harvest, when plants reached the size useful for trading in bunches. Phenolic acids contents were determined in shoots and pseudostem by means of spectrometric Arnova method with recalculation onto caffeic acid. Performed study revealed that shoots contained significantly more free phenolic acids as compared to the pseudostem. Referring to the field cultivation, the component concentration in shoots was 0.23 mg·100 g^-1 FW, whereas due to forcing 0.135 mg·100 g^-1 FW, on average. Contents of phenolic acids at pseudostems of studied plants from the field cultivation were 0.05 mg·100 g^-1 FW, while at forced plants 0.04 mg·100 g^-1 FW. No significant differences related to the level of phenolic acids between common onion and shallot were found, both in shoots and pseudostem. However, shoots of Welsh onion contained significantly less phenolic acids, regardless the cultivation place and cover application. The accelerated field cultivation resulted in shoots of Welsh onion was 0.19 mg·100 g^-1 FW phenolic acids in FW, whereas the greenhouse forcing 0.11 mg·100 g^-1 FW. Regardless the species, forced plants contained considerably less phenolic acids (namely in shoots) as compared to plants grown in the field.

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