Translation guide
In Japanese, 'dry grass' can refer to dried plant material used for various purposes, or simply grass that is not wet. The most common term is 干し草 (ほしくさ), which specifically means hay or dried grass used as animal feed. Other expressions exist for different contexts.
Dried grass used as fodder or material
The standard word for hay or dried grass, especially when used as animal feed or bedding. Literally 'dried grass'.
馬に干し草をあげた。
I gave hay to the horse.
納屋には干し草が積んである。
Hay is piled up in the barn.
A more formal or technical term for dried grass/hay, often used in agricultural contexts. Can also be read ほしくさ in some contexts, but かんそう is common in compounds.
乾草は家畜の飼料として重要だ。
Hay is important as livestock feed.
Grass that has become dry, e.g., in a field or lawn
Refers to dead or withered grass, often brown and dry. Commonly used for dry grass in fields or lawns.
庭の枯れ草を刈った。
I cut the dry grass in the garden.
枯れ草が風で舞い上がった。
Dry grass was blown up by the wind.
Literally 'dried grass', a descriptive phrase. Can be used when emphasizing the dryness, but 枯れ草 is more natural for dead grass.
乾いた草は火がつきやすい。
Dry grass catches fire easily.
Dried grass used for thatching, weaving, or other traditional crafts
Specifically refers to grass used for thatching roofs (miscanthus or similar). Not everyday vocabulary.
この屋根は茅で葺かれている。
This roof is thatched with grass.
If you mean dried herbs or marijuana, use 乾燥ハーブ (かんそうハーブ) or slang terms. 干し草 is specifically for grass/hay.