Is there a rule of thumb to go by when you should start thinking about feeding in the spring? Temperatures consistantly in the 50s (F) perhaps?
You have vast country. In some places you have continous summer (for bees) and some places you have snow cover.
In our country beekeeping area is about 600 km from south to north. I think that only Texas is 1000 km high.
0) Feed enough at autumn, so you need not to worry
1) If it is winter, let bees rest over winter
2) If they have food, dont feed them. It is vain. Look inside hive and try with hand the weight.
2b) If you feed them vainly you just fill brood area.
3) Check after cleansing flight foodstore that it is enough. They accelerate food consumption at spring when they raise brood and warm up winterball fom 23C to 32C
IF YOU WANT FAST SRING DEVELOPMENT
4) 3 weeks before nature begins to bloom=gives a lot of pollen, you can stat pollen + soyaflous + yeast feeding. Mere sugar does not help.
5) When these feeded brood emerge, they get fresh pollen and hive has a lot fresh nurse bees to their brood.
I have noticed that when you give to Italians pollen patty at spring their spring development is as fast as with Carniolans.
Vain feeding potter away bees body. >They get nosema and chalkbrood.
Wintered bees need protein at spring to get back their protein balance in the body.
Mere sugar feeging starts their brood rearing and bees consume their body protein to larvas. Bees will be in bad condition soon compared that they start brood raising later.