Backyard chicken farming is a longstanding practice in Romania, with over 13 million birds raised in such systems to provide households with essential sources of eggs and meat. Despite advantages such as low production costs and the potential for organic husbandry, backyard poultry remains highly vulnerable to parasitic infections due to limited biosecurity measures and minimal regulatory oversight. This study aimed to evaluate the efficacy of a plant-based anthelmintic product in naturally infected backyard flocks. Among the 35 backyard farms examined, 24 (68.6%) tested positive for helminth infections, with prevalence rates of 51.4% for Ascaridia galli/Heterakis gallinarum, 57.1% for Capillaria spp., and 40% for Strongyloides avium. Positive households were assigned to three groups: untreated control, fenbendazole-treated, and herbal product-treated. The plant-based formulation consisted of alcoholic extracts from seven locally sourced plants, Thymus serpyllum, Calendula officinalis, Inula helenium, Tanacetum vulgare, Origanum vulgare, Artemisia annua, and Artemisia absinthium, and was administered via drinking water at a dose of 5 mL/L for seven consecutive days. Anthelmintic efficacy was assessed using the fecal egg count reduction test (FECRT). Fecal samples were collected before treatment and on days 7, 14, and 21 post-treatment, and examined using flotation and the McMaster technique. Both the plant-based and fenbendazole-treated groups exhibited significant reductions in egg counts for A. galli/H. gallinarum (p ≤ 0.00001), although neither treatment reached the 90% efficacy threshold required for reliable parasitic control in poultry. The herbal formulation achieved a 91.33% reduction in fecal egg counts overall and a complete (100%) efficacy against Strongyloides avium at 7 and 21 days post-treatment, respectively. At 14 days post-treatment, the mean FECRT values across all parasite species ranged from 13.64% in the untreated control group to 71.86% in the fenbendazole-treated group and 67.11% in the herbal-treated group. The highest reduction was observed in the fenbendazole group against Ascaridia galli/Heterakis gallinarum (85.22 ± 11.86), while the lowest was recorded in the control group against S. avium (–31.63 ± 96.64). Overall, our findings indicate that plant-based anthelmintics are a promising, environmentally friendly option for organic backyard poultry systems, offering a viable alternative to conventional chemical treatments.