Giving them space to expand, at the right time, will avert swarms and build massive colonies. ... Is what I do and achieve hives stacked 5 to 8 deep boxes high mid summer that are stuffed with bees. Massive workforces bringing in copious amounts of nectar in a short period.
However, there is a threshold population size where no matter how much more space is added the colony instinctively goes into reproductive mode (swarm) regardless of what the beekeeper does. In my experience, the tipping point at which swarm cells start showing up is a nest of between 8 and 10 fairly full brood frames. I am talking brood, not resources nor number of boxes. When a colony is approaching that level, cut them back to 4 or 5 brood frames by taking away brood frames for new colony startups (building nucs) or boosting the other weaker colonies nearby.
Double queen colonies can exceed that threshold of 8 to 10 brood frames to around 15 to 18 frames of brood before the switch is flipped. Provided the beekeeper is proactive and stacks the skyscraper at the right time. I believe is due to the extra queen pheromones circulating more strongly throughout the hive.
That is the threshold for my bees that I raise myself. Other strains, genetics, may have tendency to go when smaller or when bigger. You will have to figure out what you have based on observation and your notes of the size of the nest when swarm cells first start showing up. How good are your historical notes, Bob? I recall you having swarming problems last spring. Review your notes to reveal this threshold for the bees and hardware that you have. Then do your best manage the brood nest under that threshold.
High level brief on swarm control:
- from past inspection notes, figure out the brood nest size threshold for the bees you have and the equipment you are keeping them in.
To avert swarming, there are two separate entities in the colony that have to have their needs satisfied.
- The queen. She needs to have 3 frames of empty comb available to her in the brood nest at all times. At each inspection, the beekeepers job is to assess the size of the nest and adjust the brood frames to satisfy her need and keep the nest size under the threshold.
- The bees. They need 2 to 3 completely empty frames (no bees) of space for each frame of brood counted in the brood nest. This is over and above whatever frames are already in the hive that are already occupied (mostly covered) by bees. This is space just for the new bees to live when they emerge. To this, you must also add workspace -honey supers- for the amount of flower flow that is on at the time of inspection.
If the beekeeper is not satisfying those needs of the two entities nor mindful of the nest size threshold ... that person will soon not be a beekeeper, they become a bee hadder ... because the bees will leave in swarms. Satisfy those two needs at each inspection to keep the bees in the boxes (bee-keeper), and you will rarely have swarms. That is until the hive reaches the size threshold noted.
Hope that helps!