When it comes to adding a second brood box, there’s one single sign to look for.
And that sign is… not enough space.
Bees will fill up all the space they have in their hive with comb, brood, pollen and nectar, so you only really need to get a second brood box once your bees have filled up almost all the cells in the first one.
The simple reason for this is that it’s necessary for the queen to have enough space to lay her eggs in.
If she runs out of space and can’t find a good cell to lay an egg in, she’ll have to lay it in a poorly prepared cell. This is called “mis-laying.”
Mis-laid eggs aren’t viable, and they’ll die off within a few days. You’ll be able to tell when this has happened because mis-laid eggs will be sunken into the cell, rather than standing tall.
By the time you see your first mis-laid eggs, it’s already too late. The queen will keep on mis-laying until you give her more space to lay in, and the hive will be hopelessly queenless within a month.
It’s not really a big deal, though. All you’ll have to do is buy a new queen and introduce her to the hive, and your bees will be back on track in no time. You’ll probably find that your bees are going to be a lot happier with a younger queen.
That’s all there is to it. There’s nothing to worry about. Just make sure you add a second brood box as soon as you see a frame or two with cells full of nectar taking up all the space on it. That’s the sign to look for, and it’s a surefire one.
Oh, and before I forget, one thing you must never ever do is to add a second brood box which is empty. If you do that, your bees will just fill it up with comb, and you’ll end up with a brood box with misshapen and irregularly spaced frames. That’s bad because you won’t be able to remove the frames for inspection, and you won’t be able to easily remove the frames to harvest the honey.
One other thing you must never ever do is to add a second brood box before your bees have made a good start on filling up the first one. That’s because bees need to be able to defend the entirety of their hive, and if you add a second brood box too early, your bees will end up having to defend an area that’s just too large for them to handle. The result of that will be robbing, which is when bees from other hives take advantage of a weak hive by stealing their nectar and honey. Robbing is bad, and it can completely destroy a weak hive.