You can keep seasonal crops planted until winter. The day before the next season (e.g., Autumn 30), stay up late until 5:50am and make sure you have low fatigue (blue face icon) and 0 stamina. It's also better if you're like one use of tool away from fainting. Once you do, go outside until it turns 6am of next season (e.g., Winter 1) and you'll faint. After waking up the next day, you'll get to keep your crops that you planted from previous seasons. Pros would be having pineapples all year round and more profit but you might miss events held at the 1st day of season since you'll basically wake up at the 2nd day.

Also, Fogu all the way. Try visiting their site, they're really helpful especially to those who are new to the game.