The growth of plants highly depends on the soil’s water availability and properties. Hydrogels (HGs) have been used for decades to enhance soil water retention, whereas developing eco-friendly and sustainable HGs for agricultural applications is still necessary to ensure water and food security. In this study, renewable and cost-effective HGs were prepared from all-lignocellulose fibers of date palm biomass after carboxymethylation followed by citric acid (CA) crosslinking. HGs showed high equilibrium swelling capacity (EWC%), even in salty media, whereas purified HGs showed about 700–400 EWC% in deionized water. Further, HGs’ effect on germination was studied on Chico III tomato, mint, Basilico red, and chia seeds. The results revealed that HGs enhanced the soil properties, with taller and healthier plants observed in HG-amended soil. FTIR, thermal analysis, and microscope imaging were utilized to evaluate HGs’ and raw materials’ characteristics. The findings in this study support the idea that all-lignocellulose could be used for HG production without separation.