Bearding is the result of heat and/or overcrowding inside the hive. The hotter the temp the more bees hang out on the porch so that the HVAC bees can do their airconditioning. The more bees in the hive and less room also produces more bees on the porch. Cooler temps will allow more bees to remain inside.
when you have high temps and crowded hives you usually end up with swarming. The use of slatted racks produces somewhat of an end run around the too hot/overcrowding problem before the hive switches to swarm mode. They give you more time to respond by supering.
I've seen hives that were too hot and too crowded swarm as late as September, so don't get complaicent thinking swarm season is over for the year.