(aka: Agapanthus 'Midnight Star') Agapanthus 'Navy Blue' is the most popular agapanthus selection in the UK and much of Europe. This deciduous selection has also shown incredible winter hardiness in open field trials in western Michigan (zone 5b/6a). Starting in July (NC), Agapanthus 'Navy Blue' is topped with sturdy 4' tall stalks, each ending in medium-sized clusters of dark royal-blue flowers, which continue well into August.