After the O-bon festival in August, the gap between the temperature at day and night gets bigger. While cities in the mainland still experience the lingering summer heat, you can already feel autumn around the corner in Hokkaido. The trees begin to change colors, so you can be the first to enjoy the foliage.
If you are visiting during Autumn (September～November),
Average temperature: 16.3℃～3.2℃ (61.3℉～37.8℉)
Clothes: The morning and night will start to get colder, so it would be best to bring a light down jacket or a thick coat.
Often times Halloween is perceived as a "costume party" in Japan. However, in Europe and America, it is a seasonal festivity to give thanks to the autumn harvest and fertility. Otofuke-cho, a town with an active agriculture industry, celebrates Halloween like farmers, hosting food festivals to appreciate fresh harvests and making Jack-o'-lanterns with pumpkins.
In the Tokachigawa region, which has an active agriculture industry, you can enjoy various pastoral sceneries such as verdant soybean farms and sunflower farms before the harvest, dried and threshed straws after the harvest, and pasture rolls used as fertilizer for dairy farming lying out in the fields. These sceneries will give you a sense of nostalgia. Sometimes, farmers plant sunflowers as fertilizer (green manure) after harvesting wheat. They take the harvest and plant it back in the ground to create sunflower fields resembling a yellow carpet. The vivid sunflower field is a gesture of appreciation and hope for next year.