The Japanese word for spinach is
ほうれん草

ほうれんそう - hourensou

spinach

Japanese Definition

spinach
1. 名詞. 菠薐草

菠薐草
1. n. spinach
2. n. Usage: The first two kanji are extremely rare; the second character appears to be used only in this term. These two kanji are often replaced with the kana spelling, as ほうれん草.
3. n. Usage: As with many terms that name organisms, this term is often spelled in katakana, especially in biological contexts, as ホウレンソウ