Crops tend to be season-specific both in Harvest Moon and in Rune Factory. Those of us who have been playing Harvest Moon games for a number of years became accustomed to a specific correspondence between Crops and their seasons.
Whether motivated by a sense of mischief or simply by a desire to 'mix things up' to make the games more challenging, some of the seasonal correspondences for traditional Crops were altered in more than one recent Harvest Moon and Rune Factory game.
For example, in Rune Factory 2, Turnips, always designated as a Spring Crop, became a Winter Crop. Pink Turnips instead were designated as the Spring Crop. Onions, traditionally a Summer Crop, became a Spring Crop. Potatoes, always associated in Harvest Moon with Spring, became an Autumn Crop. Confusing? Most definitely.
I believe that Pumpkins, traditionally a Summer Crop in most Harvest Moon/Rune Factory games, were moved to Autumn in Tree of Tranquility. (That makes more sense in terms of an Autumn Pumpkin Festival in a way but I believe that Pumpkins will continue to be classified as a Summer Crop in most games.)
When I wrote a post about Crops in Island of Happiness, and described a field in error as containing 'Tomatoes, Corn and Turnips', it probably was due partly to the many changes I have experienced as a Farmer in Harvest Moon and Rune Factory. Of course, the third Crop in the field consisted of Onions, not Turnips. (In my defence, I wrote the post after a virtually sleepless night, battling a rather nasty infection that caused high fever, terrible headaches, earache and sore throat.)
Another fact that has complicated my Farming expertise somewhat is the ability to grow Crops from ALL seasons simulaneously on Whale Island in Rune Factory Frontier, making it quite possible to have Corn, Tomatoes and Turnips on the same field... Nonetheless, it is embarrassing to make a mistake like that in a published post, and I am glad that some one caught it quickly!
One can become so accustomed to our Harvest Moon universe, certain fundamental rules relating to farming, mining, fishing and even social interactions that appear to be writ in stone... the unverse therefore is intensely real and one sometimes expects that these rules, like the 'laws of Nature' are unchanging. Making ANY assumption in a new game that is based on past games is a mistake unless proven by actual experience because the creators of any game are like Gods who can, in a single act, reverse any or ALL of the laws. The worlds of Harvest Moon and Rune Factory are detailed and complex, with characters who appear in more than one game and items, such as lithographs, Pirate Treasure, Fossils of Fish and Wonderfuls that acquire their own reality due to Harvest Moon, irrespective of any separate identity they may or my not possess in the 'real world'.
It is important for any Harvest Moon or Rune Factory player, myself included, ALWAYS to read the description of any item in any new game. Any bag of seeds that you purchase comes with a detailed description, including its Seasonal correspondence.
I never made the mistake of actually planting Turnips in Summer in Island of Happiness... but I did make the mistake of planting Turnips in Spring once in Rune Factory 2. Force of habit... and that can be a liability as well as an asset for a veteran player.