"Large-flowered hybrids are some of the most impressive, coming into their own during the summer, joined by daintier flowering varieties of clematis viticella," according to the HTA.
Plant of the Moment is a promotional plant calendar highlighting each month plants and planting ideas to help customers in their gardens.
"Dozens of clematis varieties are available, with new ones being introduced every year, so visit local garden centres and nurseries to pick the ones that appeal."
As well as "top tips" on growing clematis such as clematis "like their heads in the sun and feet in the shade" and advice to use bark or mulch, the HTA suggests colourful clematis combinations.
These include roses, honeysuckle, Golden Hop (Humulus lupulus 'Aureus') and Wisteria. Shrubs that offer support meanwhile are Camellia, yew and junipers, Holly and Japanese maples.
More information and a downloadable media pack with plant information and companion plant ideas is available at www.the-hta.org.uk/plantofthemoment.