Crops grow when the weather is warm enough but not too hot. Too-hot summer weather pauses them until things cool down. (I think of it as a drought stunting their growth, though as far as I know the amount of rain makes no difference.) There's a table posted somewhere showing each crop's temperature range. Off the top of my head, pumpkins are first to stop (along with orchards).
Newly planted crops lie dormant until the weather becomes warm enough. I guess beans are first to start growing, and this is why they can reach such a high % of yield before early summer.
"Not warm enough" is one thing, actual frost and snow another. That kills whatever % of seeds farmers plant before the thaw. With single-farmer fields especially, many fields fortuitously escape damage thanks to the delay while farmers, who want to start planting regardless, finish whatever they'd been doing at the end of winter. I prefer to make certain by de-assigning them for the winter.
(I wish there could be a global work/don't work button for all fields at once.)
In the interval between finishing planting and starting harvesting, does it make any difference at all how well the crops are tended?