。
She sowed vegetable seeds in the garden.
Literal
She [topic-は] garden [in-に] vegetable [possessive-の] seeds [object-を] sowed.
種をまく ('to sow seeds') uses まく (蒔く/撒く), the standard verb for scattering seeds. 野菜の種 ('vegetable seeds') is a simple possessive chain. に marks the location where the seeds are placed. A practical, agrarian sentence.