The hydrothermal liquefaction of low-input high-diversity mixtures of native grassland perennials (LIHD), LIHD pretreated with dilute acid, and lignin extracted from LIHD was studied. The liquid yields were optimized using the following treatment variables: heating rate (5–140°C/min), cooling rate (5–66°C/min), reaction temperature (300–450°C, corresponding to a pressure range of 10–35MPa), residence time (1–30min), particle sizes, and catalysts (1% and 0.1% sulfuric acid, 1% NaOH, solid superacid SO 4 2− /ZrO 2 –Al 2 O 3 , and solid alkali CaO–ZrO 2 ). The liquefaction yields were found to be dependent on the final liquefaction temperature, the liquefaction time, and the heating rate. The highest liquid yield, 82.1%, was achieved within a short residence time of 1min at 374°C. The major compounds of the liquid products from the various LIHD fractions were identified by GC–MS. LIHD could be a good candidate for the liquefaction process with a fast heating rate.