GROWING CLEMATIS IN HOT CLIMATES

Many clematis can be grown successfully in hot climates. There are also some clematisthat would rather be grown in cooler environments. As an amateur gardener I will share what I have learned over the past decade.

by Lyndy Broder

I garden in the Deep South of the United States at the 33-degree latitude, the same as Northern Africa, Baghdad and Shangai. Clematis has the reputation of being difficult to grow in hot climates. I have a large garden in which only the strong survive. None of my clematis gets any special attention.

The most important factor, as with any plant is proper soil preparation and placement. I also have very heavy acid red clay soil. The addition of copious amounts of organic material is essential. I also add varying amounts of a gritty product made from expanded shale to enhance appropriate drainage. The heat, especially our hot nights, has a significant impact on which clematis can be successfully grown. When I first started to grow the atragenes (alpina and macropetala), they would do fine the first year. I was lucky if they came back the second year and none have survived into a third year. I was told that the reason they would not flourish in Atlanta was because we did not have enough cold dormancy. Our winters in Atlanta are slightly colder than they are in Portland, Oregon where atragenes do quite well. However, our summers are drastically different. 86°F ( 30°C) is the point at which plants begin suffering physiological damage from heat. The American Horticultural Society web site states: “Plant death from heat is slow and lingering. The plant may survive in a stunted or chloratic state for several years. When desiccation reaches a high enough level, the enzymes that control growth are deactivated and the plant dies.” Atlanta has 90 to 120 days where the temperature is greater than 86° F while Portland has only 14 to 30 days, which are this hot.

In the heat the hues of some clematis are not as vibrant as you see in the books when the pictures were taken in the cooler climates of England or on the web pages from Poland. Color pigments are protein that breaks down in heat. I have found that reds tend to be more vibrant in extreme heat. Perhaps the species red texensis from Texas, which is used in the breeding of many reds, is a more stable color in heat.

Despite these challenges many clematis thrive in hot climates. Those listed have flourished in my garden for a number of years. The asterisk indicates that the clematis has been listed on the International Clematis Society list of Clematis for Beginners, which can be viewed in its entirety at: www.clematisinternational.com

Clematis for the heat:

• C. ‘Alba Luxurians’*
• C. ‘Arabella’*
• C. ‘Bałtyk’
• C. ‘Betty Corning’*
• C. cirrhosa ‘Freckles’
• C. ‘Duchess of Albany’*
• C. ‘Etoile Violette’*
• C. ‘Gipsy Queen’*
• C. ‘Henryi’
• C. ‘Huldine’*
• C. ‘Jackmanii’*
• C. ‘Kakio’ (PINK CHAMPAGNE)*
• C. ‘Lady Bird Johnson’
• C. ‘Marie Boisselot’
• C. montana var. grandiflora*
• C. ‘Pangbourne Pink’
• C. ‘Polish Spirit’*
• C. ‘Praecox’*
• C. ‘Princess Diana’*
• C. ‘Romantika’
• C. terniflora* (can be invasive)
• C. x triternata ‘Rubromarginata’*
• C. ‘Viola’*
• C. ‘Westerplatte’*

Clematis that grow satisfactorily in the heat:

• C. ‘Ernest Markham’
• C. ‘The President’
• C. ‘Rouge Cardinal’
• C. ‘Ville de Lyon’
• C. ‘Warszawska Nike’*

Clematis which do not do in the heat well for me:

• C. ‘Duchess of Edinburgh’
• C. ‘Kardynał Wyszyński’*
• C. ‘Sunset’
• Alpinas
• Macropetalas
• C. montana var. rubens
• Orientalis
• Tangutica

* International Clematis Society List of Clematis for Beginners

 

I recommend that you research these clematis using the encyclopedia sectionof this web site. Some are fragrant. These clematis have a variety of growing habits from sprawling small vines to large aggressive climbers. If you have a long growing season like I do, you should add six weeks to the beginning of the bloom times as they will bloom much earlier for you. Some will rest in the heat of the summer and then bloom again in the autumn when the nights get cooler. The clematis may get brown crunchy leaves during the hottest part of the season. This is environmental and is not caused by disease. The clematis will put out fresh leaves when it gets cooler. You may prune them back after the first flush of blooms on some varieties. You can enjoy clematis blooming twelve months of the year. Beware, clematis can be addicting.

March 23, 2006

Lyndy Broder