x-Ceratostigma willmottianum Forest Blue = 'Lice' PBR
Ceratostigma wilmottianum 'Forest Blue' is a deciduous sub shrub that remains almost unnoticed for most of the year until august when it bursts into the most incredible glowing blue flowers and its fresh, neat, green leaves start to colour russet red and orange as the light levels fade.
The term sub shrub simply means it sits somewhere between a shrub and a herbaceous perennial - depending on the climate it can die right back to the ground some winters, like its true herbaceous sibling Ceratostigma plumbaginoides, and pop up again in the spring; or retain a framework through to the following year. If it does, its red stems can reach a height of 1m and this unpredictability can make it tricky to place, but it surely deserves a prominent position. In fact this is a plant that should definitely be seen more than it is.
'Forest Blue' likes warmth and shelter, too cold a spot could inhibit flowering completely, so save your sunniest spot in the garden for it. A warm wall is ideal. It also performs best on poorer ground - if the soil is too rich it throws out lots of weak leggy growth, so rather then adding garden compost or manure at planting dig in plenty of horticultural grit, especially if you have heavy, wet soil. 'Forest Blue' flowers on growth made that year so any pruning needs to be done earlier in the spring. Cut the spent flowering wood back to just above the previous year's framework.
The cobalt blue flowers of this hardy plumbago are an important source of late nectar for butterflies and moths, including the incredible hummingbird hawk moth, and like other blue flowers look particularly vivid at the end of the day. Its intense colours look wonderful positioned close to the rich red leaves of shrubs like berberis or cotinus but it also goes well with other hardy flowering shrubs such as fuchsia or hydrangea. Otherwise, grow it as part of a mixed border with herbaceous perennials like crimson Knautia macedonica and red monarda or simply give it pride of place in a decorative pot on its own.