We mulched the vegetable garden with straw to retain soil moisture.

mulched 是动词 mulch 的过去式。mulch 指"覆盖物"，作为动词表示"用覆盖物（如稻草、树叶等）覆盖土壤表面"，目的是保持土壤水分、抑制杂草生长和调节土壤温度。