Although most commercial green roofs being installed in the UK are based on off the shelf green roof solutions that, in the main, consist of sedums and other succulents, some native herbs are able to survive and flourish in green roofs systems. This will be dependent on the depth and type of substrate used.
Chives (Allium schoenprasum) often appears in on sedums based roofs without having been planted. They can grow quite well even on thin layer 20mm systems, though they do tend to congregate around drainage elements where there is more water.
Horticultural varieties of herbs would generally need to be planted at greater depth and should be considered as plants more in line with a semi-intensive/semi-extensive green roof system. Native herbs, however, will survive and flourish in extensive green, brown or biodiverse green roof systems with the right depth and right amount of organic material. These native varieties can of course be used for culinary purposes, though they do not produce plentiful leaves and tend to be much stronger in flavour.
Wild Basil, Majoram, Thyme are common components of seed mixes in Switzerland and Germany. In London they are included in the London Living roof mix supplied by a number of native seed companies. Other species, such as Breckland Thyme, can be quite successful even in thin soils.
There are a number of green roofs in the world, notably a Hotel in Vancouver, where herbs are grown on the roof to be useddirectly in the kitchen. The author once visited the M&S headquarters in London, which had a number of planters on balconies, with a full range of horticultural herbs. The planters were beside the canteen kitchen and the chefs frequently appeared onto the roofs to pluck leaves from the various plants.
Native herbs can also add another dimension to a green roof - smell. One roof in Essex that has a full range of native herbs produces a wonderful aroma when walking across it, even in Novemebr and early spring long after the plants have been at there best floristically.