Harlow Carr's plant of the month for October

This small but extremely delightful alpine plant will light up the garden with its electric-blue flowers

Gentiana 'Shot Silk'This month we are celebrating the autumn gentian, Gentiana sino-ornata and its many hybrids. We have a great collection of these at RHS Garden Harlow Carr after hosting a Gentian conference back in 2006 and a lot of these are now on display in the Alpine House and in the open garden around the Bath House.

The conference taught us that, in order to be successful, one really has to put the effort in: choosing the site and compost carefully; feeding regularly when in growth; and propagating in early spring. What is important is the pH, with about the optimum being 6-6.5, but it is just as damaging to have soil too acid as too alkaline. Some growers add dolomite limestone to their composts to reduce acidity. Also, although autumn gentians should never dry out, they also hate being too wet, which is odd because one of the parents of most varieties, G. sino-ornata, is a bog plant in the wild. They also like quite a lot of sun.

Gentiana ‘Shot Silk’ is widely available, this autumn-flowering gentian is one of the most showy and easiest to grow. Raised by Keith Lever of Aberconwy Nursery this plant received an AGM in 1991 (re-confirmed in 2012) and is a reliable performer throughout the country.

Its strong constitution means it can be increased by lifting established clumps in March/April. Carefully shake the clump and tease out the roots and replant into a well-prepared, lime-free and moisture retentive soil. The large, upright, funnel-shaped flowers light up the garden with their electric blue colour. The petals are shot through with a violet sheen - maybe this inspired the name.

Good companions for this diminutive autumn star include Gaultheria itoana, goat’s beard Aruncus aethusifolius as well as ferns such as Adiantum and Dryopteris.

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