Bacteria were isolated from seeds of non-native <em>Phragmites australis</em> (haplotype M) then representatives were evaluated for their capacities to become intracellular in root cells, and their effects on: 1.) germination rates and seedling growth, 2.) susceptibility to damping-off disease, and 3.) mortality and growth of competitor plant seedlings (dandelion (<em>Taraxacum officionale</em> F. H. Wigg) and curly dock (<em>Rumex crispus</em> L.)). The experiments included the following assessments of <em>Phragmites</em>-associated bacteria (<em>Pseudomonas</em> spp, strains Sandy LB4 (<em>Pseudomonas fluorescens</em>) and West 9 (<em>Pseudomonas</em> sp.)): capacity for plant growth promotion (using <em>Poa annua</em> seeds), <em>Poa annua</em> and <em>Phragmites australis</em> seed germination and seedling root architecture, disease protection (co-culture experiments with soil fungi), damping off disease control (with pathogen <em>Fusarium oxysporum</em>), and multiple competitor inhibition experiments (with <em>Taraxacum officionale</em> and <em>Rumex crispus</em> L.). In total, 10 laboratory experiments were performed, data from eight of which are recorded in this data release.