While some Australians will claim otherwise, Manuka Honey comes exclusively from New Zealand. The flowering native New Zealand Manuka tree grows predominantly on the North Island of New Zealand. To crop Manuka honey, beekeepers move their hives into areas where the Manuka is the predominant vegetation type when the Manuka is starting to flower, typically spring to early summer depending on the region within New Zealand.
The vast majority of Manuka growing in New Zealand grows as part of the successive native forest regeneration process. A mature native forest in New Zealand will typically contain no Manuka trees. But, cut down, burn, crush and otherwise clear the native forest (as the accommodating European settlers did in vast areas 100-150 years ago), plant grass, put sheep out to graze and what you have is a dormant native forest that very badly would like to reclaim that land. If the stock levels are too low to suppress it, the Manuka will start to come back as the first phase of forest regeneration. Typically this will occur on the steeper hillsides, where the sheep find it a bit harder to graze. If allowed, the Manuka will come in thick and even, covering the landscape as a shrub initially, growing to a 15-25 foot tree eventually. In this way, the Manuka creates a nursery environment for other species to slowly start to take root under the shade of the Manuka. After 50-75 years, the Manuka will be superseded by the second phase vegetation types, and die out having served its purpose in the natural cycle.
Because the growth pattern is so distinctive, locating good areas of Manuka growth is fairly straightforward, so beekeepers are able to place their hives in the right location to allow the bees to forage on Manuka nectar. Another fortunate fact of native New Zealand forests is that the other plant types that are good nectar sources typically flower either before, or after the Manuka in a given area. This greatly simplifies the task of trying to get only Manuka into the hive. Beekeepers watch closely as the season approaches and time the placement of their hives to maximize their exposure to the Manuka nectar flow. Even with all of this working for you, it is impossible to get 100% pure Manuka honey and nothing else, out of a hive. Invariably, there will be some pre or post Manuka nectar flow foraging that the bees will do. While incredibly smart creatures, the bees don’t follow human instructions well. You can’t tell them to only work the Manuka flowers.
There are some techniques you can use when harvesting the honey to segregate honey coming from different areas of the hive to increase the concentration of Manuka honey in a given batch. Astute, experienced Manuka honey producers, who have their own extraction operations, are quite good at doing so to maximize their results. But how do you know, other than by the color or taste of the honey if you have gotten the Manuka crop you went after? Fortunately, the answer is simple–you send a sample from each batch to one of the two main independent laboratories in New Zealand, and they will test the honey for dietary Methylglyoxal. Dietary Methylglyoxal, abbreviated as MG or MGO, is a naturally occurring organic compound found in high concentrations in Manuka honey. Test results are given as mg/kg, and the concentration of MG directly correlates to the health and wellness benefits of Manuka honey. Typical tests come back anywhere from 100–250 mg/kg at the time of harvest, and then this concentration changes over time as a precursor organic compound in the honey (dihydroxyacetone, or DHA) converts to MG. For a detailed explanation of these tests, and the history of how they developed, read "DHA, MG, and manuka honey activity
" by Megan Grainger, Ph.D. Student at the University of Waikato in New Zealand, and technologist at Analytica Laboratories, one of the two primary honey-testing labs in New Zealand.
Because of this propensity of Manuka honey to “grow” in activity, most honey is stored in bulk for 1-2 years prior to being packed, labeled and shipped out to retail outlets and consumers.