Rule 1: 1. The passive for general statements
The imperfect passive is the natural way to say what is habitually done: يُزْرَعُ الْقَمْحُ فِي الْخَرِيفِ wheat is sown in autumn. The perfect passive reports a single completed event: زُرِعَ الْقَمْحُ أَمْسِ the wheat was sown yesterday. In both, the former object is now the subject and the verb agrees with it; non-human plurals take the feminine singular as usual: تُقْفَلُ النَّوَافِذُ.
يُحْصَدُ الْقَمْحُ فِي أَوَّلِ الصَّيْفِ.
yuḥṣadu l-qamḥu fī awwali ṣ-ṣayfi
Wheat is harvested at the beginning of summer.
تُقْطَفُ الْأَزْهَارُ فِي الرَّبِيعِ.
tuqṭafu l-azhāru fi r-rabīʿi
Flowers are picked in spring.
Feminine singular verb with a non-human plural.
قُفِلَتِ النَّوَافِذُ لَمَّا نَزَلَ الْمَطَرُ.
qufilati n-nawāfidhu lammā nazala l-maṭaru
The windows were shut when the rain came down.