All plants and animals associate with specific communities of symbiotic microorganisms. Characterizing the diversity and functions of these communities is essential for understanding their roles in host health, however such efforts are often hindered by the dominance of host-derived material in e.g., DNA extractions. Although various commercial host DNA depletion kits have been developed to overcome these challenges, they have not yet been systematically tested on environmental samples. We used Zostera marina, globally the most widespread seagrass species, as a test case to assess the effectiveness of three different commercially available host DNA depletion kits: QIAamp DNA Microbiome Kit, HostZero Microbial Enrichment Kit, and NEBNext Microbiome Enrichment Kit, when compared to the widely used DNeasy PowerSoil Pro Kit. All three host depletion kits substantially reduced the relative proportion of host DNA, as assessed by 16S rRNA gene amplicon sequencing, and enriched previously identified seagrass-associated bacteria. Furthermore, in metagenomes, only samples processed with host depletion methods allowed for the assembly of metagenome-assembled genomes (MAGs) with high completeness and low contamination. Metagenomic analysis further enabled the recovery of seagrass root core microbiome members, including previously undetected members of the family Sedimenticolaceae, highlighting the value of these techniques for uncovering novel host-associated microbial diversity in environmental samples such as marine plants.