We fertilize all winter here in our part of Florida. Even though we do get cold here it's still a pretty mild winter with a few freezes thrown in like tonight. We are suppose to get down to 28° so that means at the garden 4 miles down the road it will be around 23°; it's always about 5° colder there for some reason. We fertilize with water soluble fertilizer like Miracle-Gro and also use Daniels Plant Food. The slow release doesn't release anything if it's under 70° so they won't get fed that way unless we warm up above that. We have almost year round growing so we continue to feed the plants year round.
