I have worked with many novice beekeepers who lost colonies because they either did not feed the bees at all or they did feed, but at the wrong time. Here’s the advice I offer them. The dates are for Fredericksburg VA. If you live in a colder or warmer place, you’ll need to adjust the dates accordingly.
There are three reasons we might feed sugar to our bees: they are starving now, they will starve later if we don’t feed them now, and there is not enough nectar coming in to stimulate or support adequate brood rearing.
If the bees are starving now and nighttime temperatures are 50 degrees or more, run (don’t walk – they are starving!) to find a jar with a screw top lid and put some hot tap water and sugar in it. Poke five or six small holes in the lid, put it on the jar, shake well to mix the sugar and water together, and turn it upside down over the hole in the center of the hive’s inner cover. Surround the jar with an empty box and replace the outer cover. If nighttime temperatures are lower than 50 degrees, run and get a bag of white granulated sugar and a spray bottle or drinking glass full of water. Dump some sugar on top of the inner cover around the hole and sprinkle or spray enough water on it to dampen the sugar but not have water running down into the hive.
Whew! Now that the emergency has been temporarily addressed, you can take the time to mix up some syrup at two parts sugar to 1 part water. If it is too cold for syrup, go buy a few more bags of sugar and a spray bottle. You must keep feeding the bees until the nectar flow begins. Note: if the colony is starving in cold weather, and either the cluster is very small or located low in the hive, you might consider spreading a single layer of newspaper on the top bars and dumping the sugar on that. This makes it a little easier for the bees to reach the sugar. A strong colony usually won’t have problems reaching sugar on top of the inner cover.
If the bees will starve later if you don’t feed them now, you are either in the middle of a summer dearth (very little or no nectar coming in) or you are in winter or early spring and the bees will run out of honey before the spring nectar flow starts. If it is cold out, go buy some sugar and keep a small, damp pile of it on the inner cover at all times. Start by giving them maybe a half pound and then see how much (if any) they’ve taken in three days. Adjust the dosage accordingly and monitor at least weekly. I wouldn’t just dump a ton of sugar on the lid without checking how much they actually take, because you’ll want to get the lid off eventually and it is a pain to have to manage a lid covered in damp sugar.
If it is summer and the bees are not putting on winter stores, feed them syrup of two parts sugar to one part water. Keep the syrup coming until one of two things happen: they have adequate honey stores for winter, or you get to the first week in October. If they get a full winter store on before October, cut the syrup back to a pint of one part water to one part sugar per week. This will keep the queen stimulated to lay the eggs that will become your winter cluster, but will not tend to plug up the brood nest with honey.
If they haven’t got a full winter store on, don’t let them run out of syrup until October. Then, regardless of how much honey they have stored, take the syrup off. Feeding later than October creates high humidity in the hive, and all that water will condense during cool evenings to drip water on your bees and kill them. It also can lead to mold in the hive and in some cases, to the colony abandoning the hive. If the bees don’t have full winter honey stores on by early October, either make fondant or put damp sugar on the cover. Note: this is no small task. A strong colony might take three to five gallons of syrup a week during the summer.
If there is not enough nectar coming in to stimulate or support adequate brood rearing, you are either in late winter/early spring or you are in late summer/early fall. Speaking very broadly, the queen’s egg laying rate fluctuates with the amount of nectar coming into the hive. In spring, you might want to stimulate brood rearing before your main nectar flow to increase the hive population quicker to take better advantage of the nectar flow. I don’t bother with this, because the nectar flow here starts very early (mid or late March). As long as the bees have enough stores to keep them going till the flow, I don’t feed them in the spring.
Late summer/early fall is a different matter entirely, because you want the population to build up so you have lots of very young, well fed bees to make the winter cluster. Eggs laid in September will become the adult bees making up the winter cluster. You do not want the queen to reduce egg laying in September! If you are feeding to build winter stores, you will be stimulating brood rearing at the same time. If the colony has adequate winter stores, you can feed a pint of 50/50 syrup per week. That’ll keep the eggs coming without jamming up the brood nest with honey.