The cliff rose (Armeria maritima), like other halophytes, has a phenolics-based antioxidant system that allows it to grow in saline habitats. Provided that antioxidant properties are usually accompanied by antimicrobial activity, in this study we investigated the phytochemicals present in a hydromethanolic extract ofA. maritimaflowers and explored its antifungal potential. The main phytocompounds, identified by gas chromatography–mass spectrometry, were: hexadecanoic acid, octadecanoic acid, 9-octadecenoic acid, 3-(3,4-dihydroxy-phenyl)-acrylic acid ethyl ester, and benzeneacetaldehyde. The antifungal activity of the extract and its main constituents—alone and in combination with chitosan oligomers—was tested against six pathogenic taxa associated with soil-borne diseases of plant hosts in the family Cucurbitaceae:Fusarium equiseti,F. oxysporumf. sp.niveum,Macrophomina phaseolina,Neocosmospora falciformis,N. keratoplastica, andSclerotinia sclerotiorum. In in vitro tests, EC90effective concentrations in the 166−865 μg·mL−1range were obtained for the chitosan oligomers–A. maritimaextract conjugate complexes, lower than those obtained for fosetyl-Al and azoxystrobin synthetic fungicides tested for comparison purposes, and even outperforming mancozeb againstF. equiseti. In ex situ tests againstS. sclerotiorumconducted on artificially inoculated cucumber slices, full protection was achieved at a dose of 250 μg·mL−1. Thus, the reported results support the valorization ofA. maritimaas a source of biorationals for Cucurbitaceae pathogens protection, suitable for both organic and conventional agriculture.