I’m in the middle of Winter 2, cranking out plenty of crops by using Winter seeds and crafting the grown plants back into Winter Seeds. However, if my math is correct, I’m going to end up with 4-5 days at the end of the month where my fields will be barren. Can I use either of the Speed Gro fertilizers to speed up the growth of these plants?
SpeedGro makes your crops grow 10% faster. So with winter crops that take 7 days to produce, it will reduce the grow time by 1 day (assuming that it will round up from .7 days). In your case, using SpeedGro still won't give you enough time to produce a harvest in the 4-5 days you will have leftover. Don't worry about not producing anything in those 5 days, you can of course still be productive by using these days to mine or upgrade your farming tools.