knee-high by the Fourth of July UK /ˌniːˈhaɪ baɪ ðə ˌfɔːθ‿əv d͡ʒʊˈlaɪ/US /ˌniˈhaɪ baɪ ðə ˌfɔɹθ‿əv d͡ʒəˈlaɪ/ saying1 •(US) If a corn (maize) crop planted in spring has grown knee-high by the Fourth of July (Independence Day of the United States), a bountiful harvest is expected.
