Curly-leafed and turnip-rooted parsley have recently been introduced to Greece as alternative herbs within the programme for crop diversification. Because the response of these subspecies to nitrogen (N) application under the warm climatic conditions of the Mediterranean region is unknown, both were cultivated over three consecutive years in order to evaluate their yield potential and quality (in terms of nitrate content) in relation to nitrogen application in comparison with the traditionally cultivated plain-leafed subspecies. Nitrogen was applied as ammonium nitrate in the form of liquid feeds at rates of 30–450 mg kg−1. Foliage and root yield increased with N application up to a level of 150 mg kg−1 and the nitrate content of the tissues was low. Increasing N application rates to 300 or 450 mg kg−1 did not cause a further increase in yield, but the nitrate content of the tissues increased. In view of health concerns with respect to human nitrate intake and environmental threats posed by excessive N application, it is concluded that the optimum level of ammonium nitrate application under local conditions should be 150 mg kg−1. Overall, all three subspecies responded to N in a similar way in terms of yield and nitrate content.