The general opinion is that Heather honey contains to much anti oxidants and thus will give diarrhea and all Heather honey must be removed. Heather honey is popular and sell at higher price so its fair to consider if that is part of the reason for the opinion?
But fair is fair diarrhea can of course happen since they need to wait until they can fly in the spring before they can relieve themselves, so when they are full then it happens.
Over to science: first of all they use very little food in order to to keep the cluster, about 1 kg per month (1), (5) so its not the wintercluster that causes the diarrhea or possible starvation, it is when they start to brood. Therefore it is of most importance that they dont start the brooding too early because then the food consumption goes up and they could be in trouble. To avoid this the hive needs to be ventilated from the bottom (2) to not start the brooding too early. Once they started there is no turning back since the brood need higher and more constant temperature with increased food intake and greater risc for diarrhea.
But its all good with theory what about experience – does anyone winter in on heather? Sure there is, its quite common in UK (3), (4) Chainbridge honey have about 2000 hives and they winter in on Heather and Ivy honey.
What about our own experience? Last year was a fabolous Heather year and we got loads in our hives so we let them keep 6-8 kg of Heather honey and filled up with sugar. In march we gave them another 1-2 kg to boost the spring brooding and all our 9 hives survived with no issues whatsoever. Now would we use 100% Heather – probably not since also we are a bit greedy;) We would trade some of it with other honey but we are definitly not afraid to let them have Heather. In fact one of the tests we plan to carry out this autumn is to try one hive with 100% Heather – if we get any heather this year that is.
To summarize: there is no issue to let them have some frames with Heather. Too sealed hives with poor ventilation will probably cause problems.
Finally: What does Bertha the bee think? “All honey is yummy
(1) Åke Hanssons bok, sid 328 för beräkning av foderåtgång
(2) Jano’s krönikor i bitidningen 2017
(5) Jano’s blogg kapitel övervintring