(first post here, yay! I'm sorry if this was suggested already.)
1) Annual growth cycle
Today, as it stand, there are two kinds of crops, all of which are destroyed entirely when harvested:
-Aboveground crops: these can be planted all year round, but with the caveat that only crops native to the biome can grow.
-Underground crops: these can be grown anywhere, but only during a certain period of the year.
The thing is: evolution-wise, this doesn't make that much sense.
More than a few meters unter the surface, temperature is almost constant all year round. Around temperate latitudes, it's always around 12°C. This is why, even at the top of a heat wave, if you have a cellar you can refresh yourself by entering it. For underground plants, it makes little sense to stop growing during a period they can barely discern at all, if even. One could assume that says, the plant of the genus Triticum that would one day become the cave wheat we've all come to brew and love would rapidly lose its growth patterns, made anarchic by the lack of any trigger for its growth season.
On the other side, aboveground plants in temperate biomes just simply cannot be cultivated in winter without at least a greenhouse: the plant either doesn't recieve enough sunligt or simply freezes and dies. All but the extremely oceanic environements show similar patterns. On the tropics and the equator, the problem is lessened as temperature variations are a lot less extreme. Hence, you should only be able to grow even local plants within a reasonable boundary of time. As a bonus, during a short period of time in the summer, you actually can cultivate stuff from hotter biomes! They would wither and die even during spring and autumn, but as the temperature is at its highest they can briefly live.
tldr: Subterran crops should live all year, unlike aboveground ones.
2) Non-annual plants
Not all plants die when harvested. Take the humble tomato as an example: after slowly growing into a vine for months, the plant starts to grow several fruits, which then ripen into delicious tomatoes. However, for some "indeterminate" varieties, the ripening isn't simultaneous: it can take a month for all tomatoes to be harvestable, after which the plant dies. In-game, this could be represented by the plant having two stages of growth, first into a green Tau symbol, then, when a batch is ready, into a red Tau. When dwarves harvest a tomato crop, it doesn't disappear, and switches back to unripe again. Approximately a week later, it's ripe again, and so on. At the 4th batch or so, the plant is exhausted and dies.
Similarily, what about perennial plants? Alfalfa is such an example in the base game. It doesn't die during the winter, thanks to its root system. Such a plant could revert to a non-harvestable, but non-destroyed stage once the harvest is over. During winter, the plant stays in the ground, and hibernates. Once more clement weather comes back, it starts growing again, and so on several times.
tldr: some plants stay rooted once harvested, and some can even survive the winter.
Edit and edit 2: got confused by a wikipedia link and briefly thought perennial plants were already in the game. Oops...