The Delights of Clematis

The Delights of Clematis

Susan Ware, KC Master Gardener 2001

Growing clematis has become a gardening passion of mine. Contrary to what you may have read, it is not difficult to grow clematis. Once planted in good, composted soil, simply take care to meet its needs and provide it with proper support, and you will be rewarded with a beautiful addition to your garden. Clematis is versatile enough for many areas of your garden. Although traditionally utilized to climb an arbor, wall, fence or trellis, European designs suggest training them to grow on trees, through shrubs, or use as a ground cover.

I have planted several types of clematis, but my first love, ‘Jackmanii’, a cultivar of C. x jackamnii, with its lush abundance of blue-purple flowers and attractive seedpods, continues to be my favorite. When in full bloom, neighbors and strangers alike stop to ask what it is and how it is grown.

A Little History

One of the first clematis, C. viticella from Spain, was introduced to England in 1569, followed in 1596 by three other European species, C. cirrhosa, C. integrifolia and C. flammula. They were all used in hybridizing programs to produce new varieties. It was not until the 19th century that the stock for the large-flowered clematis, which is so admired today, was introduced (C. lanuginosa from China and C. patens from Japan).

A heightened interest in clematis began in the 1850s and continued for several decades. Many were improved at this time, with breeding occurring in Britain, France, Belgium and Germany. More varieties were introduced during that period than at any other time in history and many clematis grown today originated from this period. In 1862, the Jackman Nursery, the leading hybridizer in Britain, introduced C. x jackmanii, still the most popular clematis grown today. Unfortunately, by the 1880s, the little understood “wilt” destroyed a large portion of commercial stocks. We now know that this “wilt” was caused by a fungus. After World War II, nurseries once again pursued large scale propagation. However, as noted, the stock for many of the popular large-flowered clematis available today originated in the 19th century.

Characteristics

Clematis (CLEM-uh-tis), from the Greek (klema) for branchlet. Yes, that is the correct pronunciation! A member of the Ranunculaceae (buttercup or crowfoot family), this genus includes approximately 250 species and numerous garden hybrids. It consists primarily of woody, deciduous climbers (a few are evergreen or herbaceous). Leaves are opposite on the stem and mostly compound with three to five leaflets. The leaf stems (petioles) twine like a tendril to provide support. They are hardy plants (many are hardy to USDA Zone 3) and can survive for 25 years or more. Clematis are not considered attractive in winter, when they are a tangle of stems and leaves. Frankly, I enjoy them even in winter as I know what comes next!

The flowers are showy, having four (sometimes as many as eight) petal-like sepals (no true petals) in numerous colors and shades; some varieties are also fragrant. The seedpod is often attractive as well. The flower color of many clematis can vary depending on flowering time, composition of soil, aspect (light or shade) and temperature. For instance, Jackmanii blooms twice over the summer in my garden. The second flush of flowers are not uniformly purple, but variegated in shades of lavender and white.

Location, Location, Location

Most varieties perform well in full or filtered sun. Although clematis prefer five to six hours of sunlight daily, they will grow in most locations, including a bright north wall. The pastel colored hybrids have more intense blooms with minimal fading if grown in bright shade or are sheltered from afternoon sun.

Generally, “Feet in the shade, head in the sun” is good advice. If planted in full sun, underplant with perennials to allow for a cool root environment. Choose perennials with non-invasive roots to prevent damage. As they have similar cultural requirements, roses are natural companions. I primarily partner clematis with iceberg roses (along with ferns, hostas and impatiens where there is protection from afternoon sun).

Clematis will thrive in most well-prepared soils (loose, well-drained and enriched with organic matter) as long as there are no extremes of acidity or alkalinity.

The site should be open enough to allow for circulation and the benefit of occasional showers. Adequate moisture is a significant requirement for healthy clematis. Naturally, clematis require a trellis or wire for the petioles to climb, unless you choose to allow the stems to grow through host plants or along the ground.

Planting

Once you have selected a healthy plant, prepare an area at least 24 inches deep in an area two to three feet wide. Add compost or other organic matter to ensure aeration and good drainage. To improve drainage in heavy clay areas, mix some coarse grit or sharp sand with the soil at the bottom of the hole before adding organic material. Clematis do not withstand much root disturbance, so take care when planting. They are often planted with the crown one to two inches below the soil surface. As always, note the recommendations for planting and care on the plant tag as they may vary according to species. Once planted, clematis may take a season to firmly establish before they begins to bloom vigorously. Some of the smaller, less vigorous clematis can be planted in containers, but the container must be at least 18” x 18” to prevent freezing.

Care and Feeding

One of the most important things to remember: Clematis require adequate moisture throughout the year. Water thoroughly and deeply during the hot summer months or any dry season. However, please note that the site should have good drainage as clematis will falter if the soil becomes waterlogged.

Fertilize in spring and again in early summer with a balanced fertilizer.

To Mulch or Not to Mulch?

Mulching can be beneficial to keep the roots cool and moist, but do not place mulch within eight inches of the stems. This can cause the stems to rot. One alternative is to plant a ground cover or perennials to shade the base of the clematis.

Support

Clematis climb by twisting petioles, or leaf stems; the vine itself does not twine. So your choice of support should be no more than a quarter-inch wide. Clematis is a very determined climber and will quickly entangle itself in its own stems if given insufficient opportunities for reaching out. I know from experience! Particularly in early spring when growth is swift, check the plant often, encouraging the leaf stems to spread out over a trellis, wire or other support.

My preference is gardening wire attached to a trellis or along a wall. Fortunately, I have the advantage of a wooden trim above a brick wall so I have attached small eye hooks to attach the wire in an “espalier” design for several clematis I have planted along the front of my house. I crisscrossed the wire the first spring when the stems were beginning to grow, urging the leaf stems to spread out along the wall. The wire is not noticeable, yet allows the leaf stems to climb in several directions. Something with a rough texture such as sisal twine can also be used. If using nylon line or something similar, tie little knots at intervals to prevent the stems from slipping down.

Pruning

The main reasons for pruning clematis are to encourage them to produce flowers lower down on the plant or for vigorous growth. Although all clematis will bloom even if they are never pruned, the ones that would benefit may produce fewer, smaller flowers, or they will be high on the plant.

There are three major pruning categories, Groups A, B and C (sometimes 1, 2, 3), based on the time of the year the plant flowers. Unfortunately, a few plants cross over into several groups! Always check the plant tag or ask at your garden center. If you have inherited a clematis and know little about it, experiment. Prune just one stem as though it belongs in Group C, then watch it, comparing it to stems left alone. The plant will tell you a lot!

Group A: Deciduous and evergreen clematis that flower on old ripened wood during winter or early to late spring do not require pruning unless you want to limit size. If you decide to prune, cut back stems that have produced flowers as soon as they finish blooming. Do not cut any trunks, and leave the larger, woody stems unless you need to radically reshape the plant. Some popular examples: C. armandii, C. montana, C. alpina and the cultivar ‘General Sikorsi’ .

Group B: This group comprises plants that have large flowers on old wood in late spring, then smaller flowers in late summer on the current year’s growth. Most clematis with double or semi-double flowers belong in this group. These plants do not require major pruning; only dead and weak stems should be removed in late spring immediately after the earliest flowering. Examples: ‘Guernsey Cream’, ‘Henryi’ and ‘Will Goodwin’.

Group C: This group comprises species and cultivars that bloom on new growth, anytime from mid June to fall, some flowering repeatedly all summer long. These plants require annual pruning in late winter or early spring. No later than March in most areas, cut the plant down to approximately 12 inches from the ground, just above a pair of plump, healthy buds. Some examples: C. viticella, C. jackmanii, C. integrifolia, C. tangutica, C. terniflora and C. texensis.

Potential Problems

Wilt: Unfortunately, “clematis wilt” is a problem for certain varieties, particularly large-flowered hybrids. Small-flowered hybrids and the species and their cultivars are less susceptible to wilt. Last summer, I encountered the disease for the first time. A large portion of an established Clematis ‘Sweet Autumn’ suddenly turned brown and brittle. The culprit is a fungus, Ascochyta clematidina, which enters the stem, usually above the soil line. When infected, a portion of the vine wilts quickly, often just as the plant begins to bloom. There is no cure! You must cut the affected stems to ground level or below and discard every trace of the diseased foliage (in a sealed garbage bag). Disinfect any tools used to remove the affected stems or plant. Note: If the disease persists, remove the entire plant and replace the soil before planting another clematis. Please note that mildew is another fungus to which certain clematis cultivars are susceptible. Therefore, ensure that the soil stays barely moist, never waterlogged, and that plants are located in a well-ventilated area.

Clematis resistant to wilt include C. jackmanii (there’s my favorite again), ‘The President’, ‘Ville de Lyon’, ‘Nelly Moser’ and ‘Betty Corning’. Also, ‘Madame Julia Correvon’, like other cultivars of C. viticella, is not susceptible to clematis wilt.

Pests: Young clematis shoots are tasty to slugs and snails. As always in the garden, watch out for them as well as aphids.

Last Word

Gardeners today have renewed their interest in this lovely vine, particularly in the hardy and disease-resistant small-flowered types. I knew little about clematis when I planted one for the first time, but I thoroughly enjoy watching them grow and “put on a show”! I hope you will too!

References:

Toomey, Mary, with Everett Leeds and Charles Chesshire. Timber Press Pocket Guide to Clematis, Timber Press, 2006 (Portland, OR)

AHS Great Plant Guide DK Publishing, Inc., 1st American ed., 1999 (New York, NY).

The New York Times 1000 Gardening Questions & Answers, Workman Publishing Co., Inc., 2003 (New York, NY)

Martin, Jane C. “Growing Clematis”, Ohio State University Extension Fact Sheet

Howells, John “Howells on Clematis” http://www.howellsonclematis.co.uk/Pages/Clematis.html

Childs, Jim “7 Secrets to Beautiful Blossoms - Clematis”