Please explain the following agricultural proverbs:

This is a passage from 24 solar term song:

Cotton should be planted before the valley comes. In the dog days, that is, the hottest time, you should always hoe the ground to take care of it. Sugarcane is planted in Grain Rain, and cotton is planted in the long summer. If the sowing time of wheat is delayed, it will not germinate, and rape will be planted too late to mature and produce less oil. Around Tomb-Sweeping Day, it is suitable to grow melons and beans.