The bees will continue to raise young as long as they have food to feed the newly hatched eggs. Without brood food, a.k.a. "Royal Jelly" (also called Queen food) the colony will often consume the eggs as the queen is laying them to prevent having more mouths to feed than they can afford.
Therefore, during the growing season, it is important to supplement the colony with the resources they need to produce enough food for the family to grow and have an excess amount to store for hard times.
Bees, like us, need carbs and proteins. Nature provides nectar they use for their carbs and pollen is their protein source. Without both of these they stop raising young, which of course means they stop growing - shut down brood rearing and go dormant.
What and when we feed a colony is based on multiple factors. First we determine the goals we have for the particular hive or set of hives in question. Then we can determine what will best assist the colony to achieve the goals we have in mind for them.
For example, the hive(s) will be used for the pollination needs of my small acreage property and surrounding community - the typical needs for hives involved in property tax valuation, a.k.a. Ag Exemption. While others may be using hives to move for honey production or Pollination for crops.
In the property tax example, in the south central Texas region, feeding the bees only syrup when they will take it until they have around 50 pounds of stored honey to last them through hard times. In our area, that means the dog days of summer and the dead of our short winters. These bees are not expected to produce an excess of honey for harvest, they simply need enough to feed themselves. So feeding syrup is normally limited and pollen is rarely needed since the colony will have less population needed until the normal spring Nectar Flow.
However, if the goal is to send bees to California in January for the almond pollination event, the hives need to be strong and in brood rearing mood in order to satisfy the grower's needs to get an ample fruit set in his orchards.
Feeding Syrup: In south central Texas we feed a 1:1 ratio (1 part sugar to 1 part water) in the warm months and reduce the water to a 2:1 ratio in the cold seasons. We stop feeding when they stop taking it within a week's time frame. Sugar syrup will ferment when it is not processed within a couple of weeks or so, based on weather conditions, so we add a little bleach to the syrup when mixing to prevent mold and fermentation. (see below)
Feeding Pollen: We offer bees pollen subs when we want the colony to grow and there is no pollen coming in from the fields.
How can we tell if the bees need pollen supplements?
Don't be shy, ask them and they will tell you. You can open the hive and check the contents in the brood nest for fresh pollen and stored bee bread. If there is not much there, they are using more than they are bringing in on a daily basis, so offering subs is likely needed.
Or, you can put some dry pollen out in the area for them to find. This is a sure fire way to know if they are in need, because when they find some blooms in the fields that have fresh pollen, they will ignore the subs. Thus telling you that they no longer need any help. As long as they will take it, we like to provide it to the hives we are wanting to help grow.