Although the bees are still foraging and brood are still being laid, preparations for winter need to be thought about as early as possible, so I am trying to get ready for what might be another very cold and wet winter that could keep my bees hive-bound for 6 months or more.
The first and most obvious consideration is whether each colony has enough feed to take it through winter. How much feed they need depends on how cold your winters are, how long they go on for, when forage ends and when it might begin again, how many bees are in the colony, what kind of micro-climate your apiary is in, how healthy they are, and many other factors. There is, like so many things in beekeeping, no set rule. Some seasoned beekeepers have told me that a colony need to have a super full of stores to make sure they get through winter, but I have seen colonies survive on less and die with more. But I don't think it is a bad benchmark.
At the end of summer I will assess whether I think they are doing ok for stores or not. If I think they could do with some encouragement, I will feed them sugar syrup to get those stores growing faster before the colder weather hits them. As we slip into autumn I will switch to fondant if I still think they need some more help. Sometimes I have given a colony a block of fondant in autumn and they still have 90% of it in March! Other times they eat through it in a fortnight. There is a recipe for sugar fondant in one of my earlier posts if you fancy making your own.
Another consideration at this time of the season is whether you think any of your colonies are so small that they are unlikely to be able to get through winter on their own. Maybe they would have a better chance if they were mixed in with another colony? If you have two small to medium colonies, mixing them together can create one medium to large colony that will have a better chance of making it to spring. As you can see from this picture, I use the paper-separation method to mix two colonies together; I take the roof off one colony, get the colony into their brood box, cover the brood box with two sheets of paper (newspaper is good) and prick the paper generously with a pin, then put the second colony in their brood box on top of the paper and replace the roof. After a few days the bees will have chewed through the paper, but by that time they will have swapped scent with each other and will not fight, hopefully. I have done this many times and it has never failed, but as with everything, there are no guarantees.