New plant strengthening agents based on phytohormones for application in plant husbandry or arable cropping, preferably in fruit or wine growing. The invention relates to the use of a compound selected from the group gibberellin A4 (GA4), gibberellin A7 (GA7), gibberellin A3 (GA3), 1-naphthaleneacetic acid (NAA), N6-benzyladenine (BA) and S-abscisic acid (ABA), or of a mixture of at least two compounds selected from said group, as a plant strengthening agent, to formulations containing said active substances, as well as to a process for strengthening higher plants which is characterized in that a phytoactive amount of at least one of said compounds is applied to said higher plants, preferably to the epigeal parts thereof. Application in plant husbandry or arable cropping, preferably in fruit or wine growing, is preferred.