I used to garden only once a year. I planted in the spring (Memorial Day is the traditional planting day in Maine), and then, I harvested - ideally all at once - sometime in August. By October 1, the garden beds were neatly "put away" until next spring.
Then, I wanted to plant garlic, but garlic is planted in the fall and harvested in early summer.
And then, I started learning about succession planting, which makes a lot more sense for me, because of the very small space I have in which to garden.
Even now, in September, we could be planting a few things here in Maine. The garden isn't done, and if we have the ability to protect the plants we can increase our options even more.
I thought this was a pretty good article that lists a few things, even, we Maine gardeners, could be planting right now to harvest in October.
I guess, the lesson for me, a novice and "Adult Onset Gardener", is that the season isn't, necessarily, neatly ordered and chronological. All of it can be happening all at once. It's a delicious lesson.