In the winter I would definitely recommend fertilizing your trees although at a lower rate, such as half dose. I have found that this helps the leaves keep their dark green color, otherwise they get somewhat chlorotic by the end of the winter. What you should NOT do is fertilize in the interface between fall and winter. You do not want to induce a new growth flush when the growing season is nearing its end and the cold weather is about to come. I stop fertilizing about 1-2 months prior to the arrival of the cold weather. Once the weather is already consistently cold, additional fertilizer will not induce more growth flushes. I hope this makes sense.

-Brett

Citrus Tone Fertilizer is WAY wrong for Citrus as is every Fertilizer labeled for Citrus I've ever seen. Way low in N and way high in K. Ideal ratio is 5-1-3, superseding the previously thought ideal of 3-1-2.

I buy Peters Professional 25-5-15, which is only available in 25lb sacks.

It takes a number of nights in the 30s for my citrus to stop growing. Don't you have lots of days 70+ in winter? There is no "consistenly cold" here as it isn't terribly unusual to see January lows at 25 or highs of 100.

From what I have read about citrus fertilizer is that the 3-1-2 fertilizer ratio applies to younger citrus, and a 2-1-3 ratio applies to mature citrus. I don't recall the exact year this Satsuma was planted, but it is at least 10 years old, although it is a bit smaller than my other 2 in ground Satsuma of similar age, but is in a less ideal location, it is only about 7 ft tall, and maybe 12-15 feet wide. (It is located 150 or so feet away from my other citrus, in a less well drained and more exposed location)

Our winters are also highly variable although no 100 degree January weather here, some years we may have 80+ degree weather at Christmas, other years freezing rain. It is rare for us to have extended freezes, we go over 24 hours below freezing about once every 4 or 5 years. Instead that is somewhat common is go have many dreary overcast days with highs around 40 and lows below freezing some years. Not that it really applies to citrus, but our chill hours over the last 10 years have ranged from 500 - 1,300 with multiple years over 1,000 as well as multiple years under 650 hours.