The influence of arbuscular mycorrhiza fungi (AMF) inoculation, seaweed extract (SWE) foliar use, and their co‑applications were evaluated on the growth‑associated traits, antioxidant potential, essential oil profile, and the nutrients content of fennel plants. A factorial experiment was conducted as a completely randomized design with two factors and four replications in the greenhouse. The factors were: AMF inoculation (not inoculated and inoculated with 5 g kg−1) and SWE foliar application (0, 0.5, 1.5, or 3 g L−1). The highest root colonization percentage was recorded in plants treated with AMF + 3 g L−1 of SWE. The top recorded plant height, leaf number, leaf dry weight, biomass, thousand seed weight (TSW), total soluble proteins and total soluble carbohydrates content, antioxidant activity, and essential oil content belonged to AMF + 3 g L−1 of SWE. Furthermore, the co‑application of AMF + SWE resulted in a considerable enhancement of the photosynthetic pigments content and, in N, P, K, Fe, Zn, and Mn contents in the shoots and roots. The GC‑FID and GC–MS analysis revealed that (E)‑anethole (73.28–76.18%), fenchone (5.94–8.26%), limonene (4.64–6.58%), methyl chavicol (2.91–3.18%), and (Z)‑β‑ocimene (1.36–2.01%) were the principal essential oil constituents. The top (E)‑anethole and fenchone contents were obtained by AMF + SWE. Altogether, the simultaneous application of AMF and SWE could be introduced as an environment‑friendly strategy to reach reliable growth responses, especially in fennel plants’ enriched with some precious essential oil constituents.
