From our research it is clear that each of the different origanums we have tried is a great attractor of bees and probably all origanums are very good for bees. But, over the 5 years of our research I realised that I had accidentally mixed up some white flowering ones with the native pink that we normally sold.
It took a while to sort out where it had come from and what exactly it was. This involvedre-ordering plugs from a couple of suppliers I had used over the years and growing them to maturity to allow comparison. Eventually it was discovered to be a white variant of ‘vulgare’ that the supplier had been selling unknowingly (they thought it was pink) and even they dont know exactly what it is. This has been a happy accident as it turns out to flower for a bit longer than the native one and therefore ranks a bit higher than the others.
With a selection available, at the end of last season I took some specimens of each origanum and looked more closely at them to see why some might flower for longer than others. The obvious difference was the size of the flower head. On closer examination it is clear that the white vulgare has 5, sometimes 6, rows of flowers on each part of the flower cluster compared with 4 of the greek vulgare and only 3 in the case of our native (or at least the version I have). As each row of flowers opens in succession, closing after pollination, then those with more rows of flowers will naturally flower for longer.
Anyway, they are all really useful plants for both a herb garden, culinary supplies and provide nectar for bees (mostly honey bees but with a few bumblebees and solitary bees too) for 7 to 10 weeks depending on the plant.