It is summer. It is hot. Why, oh why, would anyone be planting a crop that grows during "cool" weather? Because, Grasshopper, fall will be here soon and we need to get the fall crops in the ground now. There are lettuce seeds, spinach seeds, beets, peas, cabbage, kale and onions that must be planted. Yea! Gardening!
I grow onions every year. Usually twice a year. Spring and fall.
Onions are a "cool season crop." This means they will grow and thrive when the weather is cool. Some other plants that like cool weather include: Brussels sprouts, cabbage, broccoli, sugar snap peas, cauliflower, beets, lettuce, spinach, radishes, asparagus, kale and many herbs. All of these will enjoy cool days and frosty nights.
Read more here.