Bí theo dâu, bầu theo mạ

Direct English translation

Plant gourds according to the mulberry season, plant bottle gourds according to the rice-seedling season.

Equivalent English version

Everything has its season

Giải thích tiếng Việt
Chỉ kinh nghiệm canh tác theo thời vụ: trồng theo vụ dâu, trồng bầu theo vụ mạ thì hợp mùa, hợp đất. Câu cũng dùng rộng để nói việc muốn thuận lợi thì phải làm đúng lúc, theo đúng nhịp công việc.
English explanation
It refers to a farming rule of thumb about seasonal timing: pumpkins should be planted in relation to the mulberry cycle, and gourds in relation to the rice-seedling cycle. More broadly, it means that things succeed when done at the proper time and in the proper sequence.