Iris (Rowden collection)

With flamboyant flowers in a range of colours and architectural foliage, water irises are an attractive addition to a pond or bog garden. RHS Garden Rosemoor is now home to the Plant Heritage National Plant Collection of these striking plants, made up predominantly of Japanese water irises (Iris ensata).

History of the collection

John and Galen Carter, former owners of pond and bog plant specialists Rowden Garden Nurseries on Dartmoor in Devon, had a passion for water irises. Their breeding programme over many years resulted in a superb collection of more than 80 cultivars. When planning their retirement, they approached RHS Garden Rosemoor Curator Jon Webster about taking on the collection to safeguard it for the future. “I was extremely pleased to accept as this was a very well documented collection containing all the named cultivars that they’d bred and was also registered as a Plant Heritage National Collection,” says Jon.

A new home for the irises

Iris ensata ‘Rowden Satrap’

Iris ensata ‘Rowden Shah’

The collection gives a wonderful display of form and colour in early summer, and though individual blooms last only a few days the flowers will continue to be produced for a number of weeks.

Species and cultivars

The collection is comprised of more than 80 Rowden hybrids across four species: from Japan, Iris ensata (Japanese water iris) and Iris laevigata (smooth iris), British native Iris pseudacorus (yellow iris) and North American Iris versicolor (blue flag), of which the largest group in the collection is Japanese water irises. The colours range from white and yellow to pale blue and dark purple, many of them with beautiful patterning. “There are a number of rare cultivars in the collection, such as Iris ensata ‘Rowden Prince’ which we managed to get through exchange with another collection holder of water iris, Tor Garden Plants,” says Jonathan. “Iris ensata ‘Rowden Knave’ initially proved difficult to maintain but since moving it to a drier area of the border, has developed well.”

Breeder John Carter used to work for the diplomatic service in the Middle East, which influenced some of the names chosen for his Iris ensata cultivars, such as ‘Rowden Sultan’, ‘Rowden Shah’ and ‘Rowden Naib’.

Iris ensata ‘Rowden Sultan’

Iris ensata ‘Rowden Naib’

My favourites are the Japanese water irises because they are one of the most dramatic species with large flowers and a great colour range.

Cultivation and care

“The collection does well at RHS Rosemoor on a site of acid clay. Iris ensata likes a heavy moist soil while I. versicolor, I. laevigata and I. pseudacorus like it on the wetter side – they thrive at the margins of large ponds or streams.” says Jonathan. “Some more vigorous forms can be made less so if planted in a slightly drier position.”

“Water irises don’t have the most robust of blooms so can be damaged equally by hot sunny days and heavy rain. Dappled shade can help them to bloom at their best and give a longer flower life. We use plants that like similar conditions, such as Hosta, Persicaria, Pulmonaria and Rheum  to keep the different cultivars apart and prevent them getting mixed up.”

A seedling is a young plant grown from seed.

seedlings

The collection as a whole offers a wonderfully diverse range of colours and markings. I particularly like the dark purple veining on the flowers of Japanese water iris ‘Rowden Satrap’ – it’s really quite striking.

Future plans

Tor Garden Plants, which took over Rowden Garden Nurseries, is starting to bulk up plant stock and sell the irises commercially again. There are further cultivars to add to the RHS Rosemoor collection, so plants are being exchanged when material becomes available to ensure this amazing horticultural legacy is preserved for the future.