Hyde Hall's plant of the month for September

The hardy plumbago enlivens autumn gardens with its sky blue flowers and dainty leaves

Ceratostigma willmottianum AGMAs the summer months slip into the rich autumnal harvest months we try and ensure the borders are enlivened by fresh bursts of colour. There are many plants that flower late in the season and a great choice to look out for is Ceratostigma willmottianum AGM. This is a small deciduous shrub that reaches around 1m (3ft) and it has an open habit with slender, slightly wiry stems.

The purple-margined leaves turn red in autumn and before that the shrub is covered in pale blue flowers that have red tubes. The soft blue flowers contrast well with the bright green foliage and are easy to associate with other colours and plants.

Ceratostigma enjoys growing in a sunny and sheltered site or in colder parts of the country against a warm sunny wall, it is easy to grow and is generally free of pest and diseases, in the spring the previous season’s growth should be cut hard back.

At RHS Garden Hyde Hall Ceratostigma grows well on the Dry Garden where it is baked by the sun all day and it will associate well with the blue architectural flower heads of Eryngium bourgatii as well as the rich purple foliage of Sedum telephium (Atropurpureum Group) ‘Purple Emperor’ AGM and the soft, fluffy foliage of Nassella trichotoma a very attractive small grass. It is also used in large drifts on Clover Hill to add to the late season colour where it combines with other late season favourites such as Sedum (Herbstfreude Group) ‘Herbstfreude’ AGM and Calamagrostis x acutiflora ‘Karl Foerster’.

One cultivar to look out for is Ceratostigma willmottianum ‘Palmgold’ which has soft yellow foliage which contrasts wonderfully with the blue flowers when they emerge. Ceratostigma is a great plant to use towards the front of the border to provide valuable late season colour and it is easy to grow which makes it an all-round winner.

Get involved

The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.